2.Data
Type
2.1.Integer
Family2.1.1.
2.1.1.Hexadecimal
Byte, UInteger and Integer
|
Option Strict On
Public Module modMain
Public Sub Main()
Dim maxValue As Byte = &HFF
Dim posValue As UInteger = &HF034
Dim negValue As Integer = &HF034
Console.WriteLine(maxValue)
Console.WriteLine(posValue)
Console.WriteLine(negValue)
End Sub
End Module
|
255
61492
61492
2.1.2.Integer
Family MaxValue
|
Public Class Tester
Public Shared Sub Main
Dim result As New System.Text.StringBuilder()
result.AppendLine("MaxValue...")
Dim maxByte As Byte = Byte.MaxValue
Dim maxSByte As SByte = SByte.MaxValue
Dim maxShort As Short = Short.MaxValue
Dim maxUShort As UShort = UShort.MaxValue
Dim maxInteger As Integer = Integer.MaxValue
Dim maxUInteger As UInteger = UInteger.MaxValue
Dim maxLong As Long = Long.MaxValue
Dim maxULong As ULong = ULong.MaxValue
result.Append("Byte ").AppendLine(maxByte)
result.Append("SByte ").AppendLine(maxSByte)
result.Append("Short ").AppendLine(maxShort)
result.Append("UShort = ").AppendLine(maxUShort)
result.Append("Integer = ").AppendLine(maxInteger)
result.Append("UInteger = ").AppendLine(maxUInteger)
result.Append("Long = ").AppendLine(maxLong)
result.Append("ULong = ").AppendLine(maxULong)
Console.WriteLine(result.ToString())
End Sub
End Class
|
MaxValue...
Byte 255
SByte 127
Short 32767
UShort = 65535
Integer = 2147483647
UInteger = 4294967295
Long = 9223372036854775807
ULong = 18446744073709551615
2.2.Integer
2.2.1.Define Integer variable and
assign value
|
Module Module1
Sub Main( )
Dim myInt As Integer = 7
Console.WriteLine("Initialized myInt: {0}", myInt)
myInt = 5
Console.WriteLine("After assignment myInt: {0}", myInt)
End Sub
End Module
|
Initialized myInt: 7
After assignment myInt: 5
2.2.2.Add two integers together
|
Module Tester
Sub Main()
Dim firstNumber, secondNumber As String
Dim number1, number2, sumOfNumbers As Integer
firstNumber = 10
secondNumber = 20
number1 = firstNumber
number2 = secondNumber
sumOfNumbers = number1 + number2 ' add numbers
Console.WriteLine("The sum is {0}", sumOfNumbers)
End Sub ' Main
End Module
|
The sum is 30
2.2.3.Integer calculation
|
public class Test
public Shared Sub Main
Dim n As Integer
' try adding numbers...
n = 16
n += 10.23
Console.WriteLine("Addition " & n)
' try subtracting numbers...
n = 24
n -= 2
Console.WriteLine("Subtraction " & n)
' try multiplying numbers...
n = 6
n *= 10
Console.WriteLine("Multiplication " & n)
' try dividing numbers...
n = 12
n /= 6
Console.WriteLine("Division " & n)
End Sub
End class
|
Addition 26
Subtraction 22
Multiplication 60
Division 2
2.2.4.Swap two integers without using a third
|
Imports System.Drawing
Imports System.Drawing.Drawing2D
Imports System.Collections
Public Class Tester
Public Shared Sub Main
Dim firstValue As Integer
Dim secondValue As Integer
firstValue = 17
secondValue = 123
Console.WriteLine("Before swap: {0}, {1}",firstValue, secondValue)
firstValue = firstValue Xor secondValue
secondValue = firstValue Xor secondValue
firstValue = firstValue Xor secondValue
Console.WriteLine("After swap: {0}, {1}",firstValue, secondValue)
End Sub
End Class
|
Before swap: 17, 123
After swap: 123, 17
2.2.5.MinValue and MaxValue of Integer
|
public class Test
public Shared Sub Main
Dim iNum As Integer
Console.WriteLine("Integer: " & iNum.MinValue & " to " & iNum.MaxValue)
End Sub
End class
|
Integer: -2147483648 to 2147483647
2.2.6.Parse Integer
|
public class Test
public Shared Sub Main
Try
Dim num_items As Integer = Integer.Parse("123")
Catch ex As Exception
Console.WriteLine(ex.Message)
End Try
End Sub
End class
|
2.2.7.Integer.GetType
|
Module Module1
Const x As String = "This is a string"
Sub Main()
Dim a As Double = 5.678
Dim b As Int32 = 123
Console.WriteLine(a.ToString)
Console.WriteLine(b.ToString)
Console.WriteLine(456.987.ToString)
Dim c As Integer
Console.WriteLine(c.GetType())
Console.WriteLine(c.GetType().ToString)
End Sub
End Module
|
5.678
123
456.987
System.Int32
System.Int32
2.2.8.Integer boolean calculation: Or, And, Xor, Not
|
public class Test
public Shared Sub Main
Dim I As Integer
I = 3 Or 4
Console.WriteLine(I)
I = 2 And 4
Console.WriteLine(I)
I = 3 Xor 3
Console.WriteLine(I)
I = Not 5
Console.WriteLine(I)
End Sub
End class
|
7
0
0
-6
2.2.9.Parse Integer variable and get hash code from Integer
|
public class Test
public Shared Sub Main
Dim Number As String
Number = "4"
Console.WriteLine(Integer.Parse(Number))
Console.WriteLine(Number.GetHashCode())
End Sub
End class
|
4
-842352756
2.2.10.Use Integer.CompareTo to compare two integers
|
public class Test
public Shared Sub Main
Dim I As Integer = 0
Dim S As Integer = 8
Console.WriteLine(I.CompareTo(S))
End Sub
End class
|
-1
2.2.11.Integer format: D10
|
Public Class Tester
Public Shared Sub Main
Dim intNumber As Integer = 12345
Console.WriteLine(intNumber.ToString("D10"))
End Sub
End Class
|
0000012345
2.2.12.Pass Integer to a function by reference
|
Module Module1
Sub ParameterChange(ByRef A As Integer)
A = 1001
Console.WriteLine("Value of A in subroutine " & A)
End Sub
Sub Main()
Dim Number As Integer = 100
Console.WriteLine("Number before function call: " & Number)
ParameterChange(Number)
Console.WriteLine("Number before function call: " & Number)
End Sub
End Module
|
Number before function call: 100
Value of A in subroutine 1001
Number before function call: 1001
2.2.13.Pass Integer to a function by value
|
Module Module1
Sub NoChangeToParameter(ByVal A As Integer)
A = 1001
Console.WriteLine("Value of A in subroutine " & A)
End Sub
Sub Main()
Dim Number As Integer = 100
Console.WriteLine("Number before function call: " & Number)
NoChangeToParameter(Number)
Console.WriteLine("Number before function call: " & Number)
End Sub
End Module
|
Number before function call: 100
Value of A in subroutine 1001
Number before function call: 100
2.2.14.Compare Integer value in If statement
|
Module Module1
Sub Main()
Dim TestScore As Integer = 80
If TestScore >= 90 Then
Console.WriteLine("Test grade: A")
ElseIf TestScore >= 80 Then
Console.WriteLine("Test grade: B")
ElseIf TestScore >= 70 Then
Console.WriteLine("Test grade: C")
Else
Console.WriteLine("Test grade: F")
End If
End Sub
End Module
|
Test grade: B
2.2.15.Integer OverflowException
|
Public Class Tester
Public Shared Sub Main
Dim A, B As Integer
Dim C As Integer
Try
A = 9999
B = 9999
C = A * B * B * B
Catch Except As OverflowException
Console.WriteLine("Overflow error detected")
End Try
End Sub
End Class
|
Overflow error detected
2.2.16.Implicit conversion of an integer to a string
|
Module Tester
Public Sub Main()
Dim iInteger As Integer = 5280
Dim lLong As Long
Dim bytByte As Byte
Dim sngSingle As Single
Dim dblDouble As Double
Dim decDecimal As Decimal
Console.WriteLine("Implicit conversion of an integer to a string: {0}", iInteger)
End Sub
End Module
|
Implicit conversion of an integer to a string: 5280
2.2.17.Explicit conversion of an integer to a string
|
Module Tester
Public Sub Main()
Dim iInteger As Integer = 5280
Dim lLong As Long
Dim bytByte As Byte
Dim sngSingle As Single
Dim dblDouble As Double
Dim decDecimal As Decimal
Console.WriteLine("Explicit conversion of an integer to a string: {0}", CStr(iInteger))
End Sub
End Module
|
Explicit conversion of an integer to a string: 5280
2.3.Byte
2.3.1.Convert the part of a Byte array
to a String with the ToString method.
|
' Example of some BitConverter.ToString( ) method overloads.
Imports System
Imports Microsoft.VisualBasic
Module BytesToStringDemo
Sub Main( )
Dim arrayOne as Byte( ) = { _
0, 0, 0, 0, 128, 63, 0, 0, 112, 65, _
0, 255, 127, 71, 0, 0, 128, 59, 0, 0, _
0, 0, 0, 192, 255, 0, 0, 128, 255, 0, _
0, 128, 127 }
Console.WriteLine(BitConverter.ToString( arrayOne))
End Sub
End Module
|
2.4.SByte
2.4.1.Display negative SByte value
using the standard numeric format specifiers and a number of specific
CultureInfo objects.
|
Imports System.Globalization
Module Example
Public Sub Main()
Dim cultures() As CultureInfo = {CultureInfo.CreateSpecificCulture("en-US"), _
CultureInfo.CreateSpecificCulture("fr-FR"), _
CultureInfo.CreateSpecificCulture("es-ES") }
Dim negativeNumber As SByte = -45
Dim specifiers() As String = {"E2", "F", "N", "P", "X2"}
For Each specifier As String In specifiers
For Each culture As CultureInfo In Cultures
Console.WriteLine("{0,2} format using {1} culture: {2, 16} {3, 16}", _
specifier, culture.Name, _
negativeNumber.ToString(specifier, culture))
Next
Next
End Sub
End Module
|
2.5.Short
2.5.1.Short Overflow
|
Module Module1
Sub Main()
Dim Value As Short = 32767
Value = Value + 1
End Sub
End Module
|
Unhandled Exception: System.OverflowException: Arithmetic operation resulted in an overflow.
at Module1.Main()
2.5.2.MinValue and MaxValue of Short
|
public class Test
public Shared Sub Main
Dim sNum As Short
Console.WriteLine("Short: " & sNum.MinValue & " to " & sNum.MaxValue)
End Sub
End class
|
Short: -32768 to 32767
2.6.ULong
2.6.1.ULong of Decimal
|
public class Test
public Shared Sub Main
Dim flags As ULong
flags = 100 ' Decimal 100.
Console.WriteLine(flags) ' Decimal.
End Sub
End class
|
100
2.6.2.ULong of Hex
|
public class Test
public Shared Sub Main
Dim flags As ULong
flags = &H64 ' Hexadecimal &H64 = 6 * 16 + 4 = 96 + 4 = 100.
Console.WriteLine(Hex(flags)) ' Hexadecimal.
End Sub
End class
|
64
2.6.3.ULong of Oct
|
public class Test
public Shared Sub Main
Dim flags As ULong
flags = &O144 ' Octal &O144 = 1 * 8 * 8 + 4 * 8 + 4 = 64 + 32 + 4 = 100.
Console.WriteLine(Oct(flags)) ' Octal.
End Sub
End class
|
144
2.7.Long
2.7.1.Long = &H1000&
|
public class Test
Public Const MASK_READ As Long = &H1000&
public Shared Sub Main
End Sub
End class
|
2.7.2.Long = 1 Or 2
|
public class Test
Public Const MASK_READ_WRITE As Long = 1 Or 2
public Shared Sub Main
Console.WriteLine(MASK_READ_WRITE)
End Sub
End class
|
3
2.7.3.MinValue and MaxValue of Long
|
public class Test
public Shared Sub Main
Dim lNum As Long
Console.WriteLine("Long: " & lNum.MinValue & " to " & lNum.MaxValue)
End Sub
End class
|
Long: -9223372036854775808 to 9223372036854775807
2.8.UShort
2.8.1.Parse UShort value
|
Public Class Tester
Public Shared Sub Main
Dim ushortParse As UShort = UShort.Parse("65533")
Console.WriteLine(ushortParse)
End Sub
End Class
|
65533
2.8.2.Display a 16-bit unsigned integer value by using each standard
format string and some custom format strings.
|
Imports System.Globalization
Module Example
Public Sub Main()
Dim value As UShort = 9
Dim specifiers() As String = { "G", "C", "D3", "E2", "e3", "F", _
"N", "P", "X", "000000.0", "#.0", _
"00000000;(0);**Zero**" }
For Each specifier As String In specifiers
Console.WriteLine("{0}: {1}", specifier, value.ToString(specifier))
Next
End Sub
End Module
|
2.9.1.Declare Double type variable and
assign value
|
Module Module1
Sub Main()
Dim EmployeeName As String
Dim EmployeePhoneNumber As String
Dim EmployeeSalary As Double
Dim NumberOfEmployees As Integer
EmployeeName = "James Bond"
EmployeePhoneNumber = "555-1212"
EmployeeSalary = 45.0
NumberOfEmployees = 1
Console.WriteLine("Number of employees: " & NumberOfEmployees)
Console.WriteLine("Employee name: " & EmployeeName)
Console.WriteLine("Employee phone number: " & EmployeePhoneNumber)
Console.WriteLine("Employee salary: " & EmployeeSalary)
End Sub
End Module
|
Number of employees: 1
Employee name: James Bond
Employee phone number: 555-1212
Employee salary: 45
2.9.2.Define double and output its value
|
public class Test
public Shared Sub Main
Dim I As Integer = 2
I *= 5
Console.WriteLine(I)
Dim D As Double = I / 3
Console.WriteLine(D)
End Sub
End class
|
10
3.33333333333333
|
2.9.3.Get Epsilon from Double
|
|
public class Test
public Shared Sub Main
Dim D As Double
D = 5
Console.WriteLine(D.Epsilon)
End Sub
End class
|
|
|
4.94065645841247E-324
|
2.9.4.Show difference precision of
Single and Double (1)
|
Module Module1
Sub Main()
Dim A As Single = 0.123456789012345
Dim B As Double = 0.123456789012345
Console.WriteLine("Single: " & A)
Console.WriteLine("Double: " & B)
End Sub
End Module
|
Single: 0.1234568
Double: 0.123456789012345
2.9.5.Single Double MaxValue and Memory Size (1)
|
Public Class Tester
Public Shared Sub Main
Dim result As New System.Text.StringBuilder
Dim maxSingle As Single = Single.MaxValue
Dim maxDouble As Double = Double.MaxValue
Dim sizeOfSingle As Integer = Runtime.InteropServices.Marshal.SizeOf(maxSingle.GetType)
Dim sizeOfDouble As Integer = Runtime.InteropServices.Marshal.SizeOf(maxDouble.GetType)
result.Append("Memory size of a Single (bytes): ")
result.AppendLine(sizeOfSingle)
result.Append("Maximum value of a Single: ")
result.AppendLine(maxSingle)
result.AppendLine()
result.Append("Memory size of a Double (bytes): ")
result.AppendLine(sizeOfDouble)
result.Append("Maximum value of a Double: ")
result.AppendLine(maxDouble)
Console.WriteLine(result.ToString())
End Sub
End Class
|
Memory size of a Single (bytes): 4
Maximum value of a Single: 3.402823E+38
Memory size of a Double (bytes): 8
Maximum value of a Double: 1.79769313486232E+308
2.9.6.Parse double value
|
Public Class Tester
Public Shared Sub Main
Dim doubleParse As Double = Double.Parse("3.1416")
Console.WriteLine(doubleParse)
End Sub
End Class
|
3.1416
2.9.7.Define and loop through double value array
|
Module Tester
Sub Main()
Dim Values() As Integer = {100, 200, 300, 400, 500}
Dim MyValues(5) As Integer
Dim Prices() As Double = {25.5, 4.95, 33.4}
Dim I As Integer
For I = 0 To 4
Console.Write(Values(I) & " ")
Next
Console.WriteLine()
For I = 0 To Prices.GetUpperBound(0)
Console.Write(Prices(I) & " ")
Next
End Sub
End Module
|
100 200 300 400 500
25.5 4.95 33.4
2.9.8.Read Double value from Keyboard
|
Module Module1
Sub Main()
Dim Salary As Double
Console.Write("Salary: ")
Salary = Console.ReadLine()
Console.WriteLine(Salary)
End Sub
End Module
|
Salary: 123
123
2.9.9.Convert Double to Integer
|
Module Module1
Sub Main()
Dim dblValue As Double
Dim intValue As Integer
dblValue = 1.2345678
intValue = dblValue
Console.WriteLine(intValue)
End Sub
End Module
|
1
2.9.10.Parse Double
|
Imports System
Module MyModule
Sub Main()
Dim num As Double = Double.Parse("12.12")
Dim denom As Double = Double.Parse("2.2")
Dim res As Double = num / denom
Console.WriteLine(res)
End Sub
End Module
|
5.50909090909091
2.9.11.Double.IsNaN()
|
Imports System
Module MyModule
Sub Main()
If (Double.IsNaN("1.2")) Then
Console.WriteLine("Not a Number.")
End If
End Sub
End Module
|
2.9.12.Double.IsPositiveInfinity()
|
Imports System
Module MyModule
Sub Main()
If (Double.IsPositiveInfinity("999999999999999999999999999999999")) Then
Console.WriteLine("Positive infinity.")
End If
End Sub
End Module
|
2.9.13.Double.IsNegativeInfinity()
|
Imports System
Module MyModule
Sub Main()
If (Double.IsNegativeInfinity("0.0000000000000001")) Then
Console.WriteLine("Negative infinity.")
End If
End Sub
End Module
|
2.9.14.Catch OverflowException
|
Public Class Example
Public Shared Sub Main()
Dim value As String
value = Double.MaxValue.ToString()
Try
Console.WriteLine(Double.Parse(value))
Catch e As OverflowException
Console.WriteLine("{0} is outside the range of the Double type.", value)
End Try
End Sub
End Class
|
2.10.Double Format
2.10.1.Double with/without format
|
public class Test
public Shared Sub Main
Dim n As Double
n = 12
n /= 7
Console.WriteLine("Without formatting: " & n)
Dim s As String
s = String.Format("{0:n3}", n)
Console.WriteLine("With formatting: " & s)
End Sub
End class
|
Without formatting: 1.71428571428571
With formatting: 1.714
2.10.2.Double format: #,###.###000
|
Public Class Tester
Public Shared Sub Main
Dim dblNum As Double = 2123.456
Console.WriteLine(dblNum.ToString("#,###.###000"))
End Sub
End Class
|
2,123.456000
2.10.3.Double format: F2
|
Public Class Tester
Public Shared Sub Main
Dim dblNum As Double = 2123.456
Console.WriteLine(dblNum.ToString("F2"))
End Sub
End Class
|
2123.46
2.11.Single
2.11.1.Calculation with Single
|
public class Test
public Shared Sub Main
Dim Amount As Single
Dim Discount As Single
Dim DiscAmount As Single
Amount = 24500
Discount = 0.35
DiscAmount = Amount * (1 - Discount)
Console.WriteLine("Your price is: $" & DiscAmount)
End Sub
End class
|
Your price is: $15925
2.11.2.Single Double MaxValue and Memory Size
|
Public Class Tester
Public Shared Sub Main
Dim result As New System.Text.StringBuilder
Dim maxSingle As Single = Single.MaxValue
Dim maxDouble As Double = Double.MaxValue
Dim sizeOfSingle As Integer = Runtime.InteropServices.Marshal.SizeOf(maxSingle.GetType)
Dim sizeOfDouble As Integer = Runtime.InteropServices.Marshal.SizeOf(maxDouble.GetType)
result.Append("Memory size of a Single (bytes): ")
result.AppendLine(sizeOfSingle)
result.Append("Maximum value of a Single: ")
result.AppendLine(maxSingle)
result.AppendLine()
result.Append("Memory size of a Double (bytes): ")
result.AppendLine(sizeOfDouble)
result.Append("Maximum value of a Double: ")
result.AppendLine(maxDouble)
Console.WriteLine(result.ToString())
End Sub
End Class
|
Memory size of a Single (bytes): 4
Maximum value of a Single: 3.402823E+38
Memory size of a Double (bytes): 8
Maximum value of a Double: 1.79769313486232E+308
2.11.3.Calcuate Single
|
Public Class Tester
Public Shared Sub Main
Dim magnitude As Single
Dim radians As Single
magnitude = CSng(Math.Sqrt(100 ^ 2 + 120 ^ 2))
radians = CSng(Math.Atan2(100, 123))
Console.WriteLine(magnitude)
Console.WriteLine(radians)
End Sub
End Class
|
156.205
0.6826226
2.11.4.Cast Integer to Short, Double to Single
|
Module Module1
Sub Main()
Dim BigInteger As Integer = 10000
Dim LittleInteger As Short
Dim BigFloat As Double = 0.123456789
Dim LittleFloat As Single
LittleInteger = BigInteger
LittleFloat = BigFloat
Console.WriteLine(LittleInteger)
Console.WriteLine(LittleFloat)
End Sub
End Module
|
10000
0.1234568
2.11.5.Precision Error
|
Module Module1
Sub Main()
Dim A As Single
'Dim A As Double
For A = 0.01 To 0.1 Step 0.01
If (A = 0.05) Then
Console.WriteLine("Reached 0.05")
End If
Next
Console.WriteLine("Done with loop")
End Sub
End Module
|
Done with loop
2.11.6.Show difference precision of Single and Double
|
Module Module1
Sub Main()
Dim A As Single = 0.123456789012345
Dim B As Double = 0.123456789012345
Console.WriteLine("Single: " & A)
Console.WriteLine("Double: " & B)
End Sub
End Module
|
Single: 0.1234568
Double: 0.123456789012345
2.11.7.Pass Single by value and by reference to a Sub
|
public class Test
public Shared Sub Main
Dim value As Single
value = 10
DoubleItByVal(value)
Console.WriteLine(value)
value = 10
DoubleItByRef(value)
Console.WriteLine(value)
End Sub
Shared Sub DoubleItByVal(ByVal X As Single)
X *= 2
End Sub
Shared Sub DoubleItByRef(ByRef X As Single)
X *= 2
End Sub
End class
|
10
20
2.11.8.Get Epsilon from Single
|
public class Test
public Shared Sub Main
Console.WriteLine(Single.Epsilon)
End Sub
End class
|
1.401298E-45
2.11.9.Parse(String) method converts an array of strings to
equivalent Single values.
|
Module Example
Public Sub Main()
Dim values() As String = { "100", "(100)", "-123,456,789", "123.45e+6", _
"-Infinity", "-1E-16", Single.MinValue.ToString(), String.Empty }
For Each value As String In values
Try
Dim number As Single = Single.Parse(value)
Console.WriteLine("{0} -> {1}", value, number)
Catch e As FormatException
Console.WriteLine("'{0}' is not in a valid format.", value)
Catch e As OverflowException
Console.WriteLine("{0} is outside the range of a Single.", value)
End Try
Next
End Sub
End Module
|
2.12.Decimal
2.12.1.Decimal.Compare
|
public class Test
public Shared Sub Main
Dim D1, D2 As Decimal
D1 = 10
D2 = 5.7
Console.WriteLine(Decimal.Compare(D1, D2))
End Sub
End class
|
1
2.12.2.Decimal.Divide
|
public class Test
public Shared Sub Main
Dim D1, D2 As Decimal
D1 = 10
D2 = 5.7
Console.WriteLine(Decimal.Divide(D1, D2))
End Sub
End class
|
1.7543859649122807017543859649
2.12.3.Decimal.Floor
|
public class Test
public Shared Sub Main
Console.WriteLine(Decimal.Floor(5.7))
End Sub
End class
|
5
2.12.4.Decimal.GetBits
|
public class Test
public Shared Sub Main
Dim D1, D2 As Decimal
D1 = 10
D2 = 5.7
Console.WriteLine(Decimal.GetBits(3).GetValue(0))
End Sub
End class
|
3
2.12.5.Decmimal calculation
|
public class Test
public Shared Sub Main
Dim Dec1, Dec2 As Decimal
Dec1 = 100
Dec2 = 200
Dec1 = Dec1 + Dec2
Console.WriteLine(Dec1)
Dec1 = --Dec1
Console.WriteLine(Dec1)
Dec1 = ++Dec2
Console.WriteLine(Dec1)
End Sub
End class
|
300
300
200
2.12.6.Divide Decimal by double
|
Public Class Tester
Public Shared Sub Main
Dim result As New System.Text.StringBuilder
Dim maxDecimal As Decimal = Decimal.MaxValue
Dim sizeOfDecimal As Integer = Runtime.InteropServices.Marshal.SizeOf(maxDecimal.GetType)
result.Append("Memory size of a Decimal (bytes): ")
result.AppendLine(sizeOfDecimal)
result.Append("Maximum value of a Decimal: ")
result.AppendLine(maxDecimal)
result.Append("Divided by one million: ")
result.AppendLine(maxDecimal / 1000000D)
result.Append("1D / 3D: ")
result.AppendLine(1D / 3D)
Console.WriteLine(result.ToString())
End Sub
End Class
|
Memory size of a Decimal (bytes): 16
Maximum value of a Decimal: 79228162514264337593543950335
Divided by one million: 79228162514264337593543.950335
1D / 3D: 0.3333333333333333333333333333
2.12.7.MinValue and MaxValue of Decimal
|
public class Test
public Shared Sub Main
Dim dNum As Decimal
Console.WriteLine("Decimal: " & dNum.MinValue & " to " & dNum.MaxValue)
End Sub
End class
|
Decimal: -79228162514264337593543950335 to 79228162514264337593543950335
2.12.8.Do calculation between Integer and Decimal
|
public class Test
public Shared Sub Main
Dim Meters As Integer
Dim Inches As Decimal
Meters = 23
Inches = Meters * 39.37
Console.WriteLine("Meters: " & Meters)
Meters = Meters + 1
Console.WriteLine("Meters: " & Meters)
Meters += 1
Console.WriteLine("Meters: " & Meters)
End Sub
End class
|
Meters: 23
Meters: 24
Meters: 25
2.12.9.Converts Decimal numbers to UInt32 values using the explicit
Decimal to UInt32 conversion.
|
Module DecimalToU_Int32Demo
Public Sub DecimalToU_Int32(argument As Decimal)
Dim Int32Value As Object
Dim UInt32Value As Object
Try
Int32Value = CInt(argument)
Catch ex As Exception
Int32Value = ex.GetType().Name
End Try
Try
UInt32Value = CUInt(argument)
Catch ex As Exception
UInt32Value = ex.GetType().Name
End Try
Console.WriteLine(Int32Value)
Console.WriteLine(UInt32Value)
End Sub
Public Sub Main( )
DecimalToU_Int32( 123d)
DecimalToU_Int32(New Decimal(123000, 0, 0, False, 3))
End Sub
End Module
|
2.12.10.Converts Decimal numbers to
SByte values using the explicit Decimal to SByte conversion.
|
Option Strict On
Module Main
Public Sub DecimalToS_Byte(argument As Decimal)
Console.WriteLine(argument)
Dim sByteValue As Object
Try
sByteValue = CByte(argument)
Catch ex As Exception
sByteValue = ex.GetType().Name
End Try
Console.WriteLine(sbyteValue)
End Sub
Public Sub Main( )
DecimalToS_Byte(8d)
DecimalToS_Byte(New Decimal(7, 0, 0, false, 3))
End Sub
End Module
|
2.13.Char
2.13.1.Char Declaration
|
public class Test
public Shared Sub Main
Dim Char1 As Char = "A"
Dim Char2 As Char = CChar("A")
Dim Char3 As Char = "A"c
Console.WriteLine(Char1 & " " & Char2 & " " & Char3)
End Sub
End class
|
A A A
2.13.2.Declare Char using 'c'
|
Imports System.Collections
public class ConvertToString
public Shared Sub Main
Dim c As Char = "A"c
Dim s As String = ""
s = CType(c, String)
Console.WriteLine(s)
End Sub
End class
|
A
2.13.3.Use CType to convert Char to String
|
Imports System.Collections
public class ConvertToString
public Shared Sub Main
Dim c As Char = "A"c
Dim s As String = ""
s = CType(c, String)
Console.WriteLine(s)
End Sub
End class
|
A
2.13.4.GetUnicodeCategory from Char
|
Imports System
Module GetUnicodeCategorySample
Sub Main()
Console.WriteLine(Char.GetUnicodeCategory("a"c))
Console.WriteLine(Char.GetUnicodeCategory("2"c))
Console.WriteLine(Char.GetUnicodeCategory("Upper Case", 6))
End Sub
End Module
|
2.14.Char Function
2.14.1.Passing Char values to Val
|
Option Strict On
Public Module Tester
Public Sub Main()
'
Console.WriteLine(Val("c"c))
Console.WriteLine(Val("1"c))
Console.WriteLine(Val("-"c))
Console.WriteLine(Val("9"c))
Console.WriteLine()
End Sub
End Module
|
0
1
0
9
2.14.2.Char: IsLetter, IsControl, IsDigit, IsLetterOrDigit, IsLower,
IsNumber
|
Public Class Tester
Public Shared Sub Main
Dim result As New System.Text.StringBuilder
Dim counter As Integer
Dim testChar As Char
Dim testHex As String
For counter = 0 To 127
testChar = Chr(counter)
testHex = "\x" & Hex(counter)
If Char.IsLetter(testChar) Then _
result.AppendLine(testHex & " IsLetter")
If Char.IsControl(testChar) Then _
result.AppendLine(testHex & " IsControl")
If Char.IsDigit(testChar) Then _
result.AppendLine(testHex & " IsDigit")
If Char.IsLetterOrDigit(testChar) Then _
result.AppendLine(testHex & " IsLetterOrDigit")
If Char.IsLower(testChar) Then _
result.AppendLine(testHex & " IsLower")
If Char.IsNumber(testChar) Then _
result.AppendLine(testHex & " IsNumber")
Next counter
Console.WriteLine(result)
End Sub
End Class
|
\x0 IsControl
\x1 IsControl
\x2 IsControl
\x3 IsControl
\x4 IsControl
\x5 IsControl
\x6 IsControl
\x7 IsControl
\x8 IsControl
\x9 IsControl
\xA IsControl
\xB IsControl
\xC IsControl
\xD IsControl
\xE IsControl
\xF IsControl
\x10 IsControl
\x11 IsControl
\x12 IsControl
\x13 IsControl
\x14 IsControl
\x15 IsControl
\x16 IsControl
\x17 IsControl
\x18 IsControl
\x19 IsControl
\x1A IsControl
\x1B IsControl
\x1C IsControl
\x1D IsControl
\x1E IsControl
\x1F IsControl
\x30 IsDigit
\x30 IsLetterOrDigit
\x30 IsNumber
\x31 IsDigit
\x31 IsLetterOrDigit
\x31 IsNumber
\x32 IsDigit
\x32 IsLetterOrDigit
\x32 IsNumber
\x33 IsDigit
\x33 IsLetterOrDigit
\x33 IsNumber
\x34 IsDigit
\x34 IsLetterOrDigit
\x34 IsNumber
\x35 IsDigit
\x35 IsLetterOrDigit
\x35 IsNumber
\x36 IsDigit
\x36 IsLetterOrDigit
\x36 IsNumber
\x37 IsDigit
\x37 IsLetterOrDigit
\x37 IsNumber
\x38 IsDigit
\x38 IsLetterOrDigit
\x38 IsNumber
\x39 IsDigit
\x39 IsLetterOrDigit
\x39 IsNumber
\x41 IsLetter
\x41 IsLetterOrDigit
\x42 IsLetter
\x42 IsLetterOrDigit
\x43 IsLetter
\x43 IsLetterOrDigit
\x44 IsLetter
\x44 IsLetterOrDigit
\x45 IsLetter
\x45 IsLetterOrDigit
\x46 IsLetter
\x46 IsLetterOrDigit
\x47 IsLetter
\x47 IsLetterOrDigit
\x48 IsLetter
\x48 IsLetterOrDigit
\x49 IsLetter
\x49 IsLetterOrDigit
\x4A IsLetter
\x4A IsLetterOrDigit
\x4B IsLetter
\x4B IsLetterOrDigit
\x4C IsLetter
\x4C IsLetterOrDigit
\x4D IsLetter
\x4D IsLetterOrDigit
\x4E IsLetter
\x4E IsLetterOrDigit
\x4F IsLetter
\x4F IsLetterOrDigit
\x50 IsLetter
\x50 IsLetterOrDigit
\x51 IsLetter
\x51 IsLetterOrDigit
\x52 IsLetter
\x52 IsLetterOrDigit
\x53 IsLetter
\x53 IsLetterOrDigit
\x54 IsLetter
\x54 IsLetterOrDigit
\x55 IsLetter
\x55 IsLetterOrDigit
\x56 IsLetter
\x56 IsLetterOrDigit
\x57 IsLetter
\x57 IsLetterOrDigit
\x58 IsLetter
\x58 IsLetterOrDigit
\x59 IsLetter
\x59 IsLetterOrDigit
\x5A IsLetter
\x5A IsLetterOrDigit
\x61 IsLetter
\x61 IsLetterOrDigit
\x61 IsLower
\x62 IsLetter
\x62 IsLetterOrDigit
\x62 IsLower
\x63 IsLetter
\x63 IsLetterOrDigit
\x63 IsLower
\x64 IsLetter
\x64 IsLetterOrDigit
\x64 IsLower
\x65 IsLetter
\x65 IsLetterOrDigit
\x65 IsLower
\x66 IsLetter
\x66 IsLetterOrDigit
\x66 IsLower
\x67 IsLetter
\x67 IsLetterOrDigit
\x67 IsLower
\x68 IsLetter
\x68 IsLetterOrDigit
\x68 IsLower
\x69 IsLetter
\x69 IsLetterOrDigit
\x69 IsLower
\x6A IsLetter
\x6A IsLetterOrDigit
\x6A IsLower
\x6B IsLetter
\x6B IsLetterOrDigit
\x6B IsLower
\x6C IsLetter
\x6C IsLetterOrDigit
\x6C IsLower
\x6D IsLetter
\x6D IsLetterOrDigit
\x6D IsLower
\x6E IsLetter
\x6E IsLetterOrDigit
\x6E IsLower
\x6F IsLetter
\x6F IsLetterOrDigit
\x6F IsLower
\x70 IsLetter
\x70 IsLetterOrDigit
\x70 IsLower
\x71 IsLetter
\x71 IsLetterOrDigit
\x71 IsLower
\x72 IsLetter
\x72 IsLetterOrDigit
\x72 IsLower
\x73 IsLetter
\x73 IsLetterOrDigit
\x73 IsLower
\x74 IsLetter
\x74 IsLetterOrDigit
\x74 IsLower
\x75 IsLetter
\x75 IsLetterOrDigit
\x75 IsLower
\x76 IsLetter
\x76 IsLetterOrDigit
\x76 IsLower
\x77 IsLetter
\x77 IsLetterOrDigit
\x77 IsLower
\x78 IsLetter
\x78 IsLetterOrDigit
\x78 IsLower
\x79 IsLetter
\x79 IsLetterOrDigit
\x79 IsLower
\x7A IsLetter
\x7A IsLetterOrDigit
\x7A IsLower
\x7F IsControl
2.14.3.Char: IsPunctuation, IsSeparator, IsSymbol, IsUpper,
IsWhiteSpace
|
Public Class Tester
Public Shared Sub Main
Dim result As New System.Text.StringBuilder
Dim counter As Integer
Dim testChar As Char
Dim testHex As String
For counter = 0 To 127
testChar = Chr(counter)
testHex = "\x" & Hex(counter)
If Char.IsPunctuation(testChar) Then _
result.AppendLine(testHex & " IsPunctuation")
If Char.IsSeparator(testChar) Then _
result.AppendLine(testHex & " IsSeparator")
If Char.IsSymbol(testChar) Then _
result.AppendLine(testHex & " IsSymbol")
If Char.IsUpper(testChar) Then _
result.AppendLine(testHex & " IsUpper")
If Char.IsWhiteSpace(testChar) Then _
result.AppendLine(testHex & " IsWhiteSpace")
Next counter
Console.WriteLine(result)
End Sub
End Class
|
\x9 IsWhiteSpace
\xA IsWhiteSpace
\xB IsWhiteSpace
\xC IsWhiteSpace
\xD IsWhiteSpace
\x20 IsSeparator
\x20 IsWhiteSpace
\x21 IsPunctuation
\x22 IsPunctuation
\x23 IsPunctuation
\x24 IsSymbol
\x25 IsPunctuation
\x26 IsPunctuation
\x27 IsPunctuation
\x28 IsPunctuation
\x29 IsPunctuation
\x2A IsPunctuation
\x2B IsSymbol
\x2C IsPunctuation
\x2D IsPunctuation
\x2E IsPunctuation
\x2F IsPunctuation
\x3A IsPunctuation
\x3B IsPunctuation
\x3C IsSymbol
\x3D IsSymbol
\x3E IsSymbol
\x3F IsPunctuation
\x40 IsPunctuation
\x41 IsUpper
\x42 IsUpper
\x43 IsUpper
\x44 IsUpper
\x45 IsUpper
\x46 IsUpper
\x47 IsUpper
\x48 IsUpper
\x49 IsUpper
\x4A IsUpper
\x4B IsUpper
\x4C IsUpper
\x4D IsUpper
\x4E IsUpper
\x4F IsUpper
\x50 IsUpper
\x51 IsUpper
\x52 IsUpper
\x53 IsUpper
\x54 IsUpper
\x55 IsUpper
\x56 IsUpper
\x57 IsUpper
\x58 IsUpper
\x59 IsUpper
\x5A IsUpper
\x5B IsPunctuation
\x5C IsPunctuation
\x5D IsPunctuation
\x5E IsSymbol
\x5F IsPunctuation
\x60 IsSymbol
\x7B IsPunctuation
\x7C IsSymbol
\x7D IsPunctuation
\x7E IsSymbol
2.14.4.Char.IsDigit
|
public class Test
public Shared Sub Main
Dim Char1 As Char
Char1 = "A"
If Char.IsDigit(Char1) Then
Console.WriteLine("The character is a digit.")
Else
Console.WriteLine("The character is a letter or symbol.")
End If
End Sub
End class
|
The character is a letter or symbol.
2.14.5.Remove white space in a string
|
Public Class Tester
Public Shared Sub Main
Dim source As String = _
Space(17) & "This string had " & Chr(12) & _
StrDup(5, Chr(9)) & "extra whitespace. " & Space(27)
Dim thisIsWhiteSpace As Boolean
Dim prevIsWhiteSpace As Boolean
Dim result As New System.Text.StringBuilder(source.Length)
Dim counter As Integer
For counter = 0 To source.Length - 1
prevIsWhiteSpace = thisIsWhiteSpace
thisIsWhiteSpace = Char.IsWhiteSpace(source.Chars(counter))
If (thisIsWhiteSpace = False) Then
If (prevIsWhiteSpace = True) AndAlso _
(result.Length > 0) Then result.Append(Space(1))
result.Append(source.Chars(counter))
End If
Next counter
Console.WriteLine(result.ToString())
End Sub
End Class
|
This string had extra whitespace.
2.14.6.Char.ToUpper
|
public class Test
public Shared Sub Main
Console.WriteLine(Char.ToUpper("a"))
End Sub
End class
|
A
2.14.7.ChrW
|
Module Module1
Sub Main()
Dim strR As String
strR = ChrW("123")
Console.WriteLine(strR)
End Sub
End Module
|
{
2.14.8.Demonstrates IsWhiteSpace.
|
imports System
Module IsWhiteSpaceSample
Sub Main()
Dim str As String
str = "black matter"
Console.WriteLine(Char.IsWhiteSpace("A"c))
Console.WriteLine(Char.IsWhiteSpace(str, 5))
End Sub
End Module
|
2.14.9.Char.Equals.
|
imports System
Module EqualsSample
Sub Main()
Dim chA As Char
chA = "A"c
Dim chB As Char
chB = "B"c
Console.WriteLine(chA.Equals("A"c))
Console.WriteLine("b"c.Equals(chB))
End Sub
End Module
|
2.14.10.Output ControlChars.Tab
|
Imports System
Imports System.Globalization
Imports Microsoft.VisualBasic
Public Class MainClass
Public Shared Sub Main()
Console.Write(ControlChars.Tab)
End Sub
End Class
|
2.15.Special Chars
2.15.1.NewLine sign: vbNewLine, vbLrLf,
vbCr, Environment.NewLine, ControlChars.NewLine
|
Public Class Tester
Public Shared Sub Main
Dim result As New System.Text.StringBuilder
result.Append("vbNewLine").Append(vbNewLine)
result.Append("vbCrLf").Append(vbCrLf)
result.Append("vbCr").Append(vbCr)
result.Append("vbLf").Append(vbLf)
result.Append("Chr(13)").Append(Chr(13))
result.Append("Chr(10)").Append(Chr(10))
result.Append("Chr(13)
'Chr' is not recognized as an internal or external command,
operable program or batch file.
result.Append("Environment.NewLine").Append(Environment.NewLine)
result.Append("ControlChars.CrLf").Append(ControlChars.CrLf)
result.Append("ControlChars.NewLine").Append(ControlChars.NewLine)
Console.WriteLine(result.ToString())
End Sub
End Class
|
vbNewLine
vbCrLf
vbLf
Chr(10)
Chr(13) & Chr(10)
Environment.NewLine
ControlChars.CrLf
ControlChars.NewLine
2.15.2.vbNewLine
|
Public Class Tester
Public Shared Sub Main
Console.WriteLine("a" & vbNewLine & "b")
End Sub
End Class
|
a
b
2.15.3.Concatenate vbTab with Integer
|
Option Strict On
Imports System
Module Module1
Sub Main( )
Dim counter As Integer
For counter = 1 To 100
Console.Write("{0} ", counter)
If counter Mod 10 = 0 Then
Console.WriteLine(vbTab & counter)
End If
Next counter
End Sub
End Module
|
1 2 3 4 5 6 7 8 9 10 10
11 12 13 14 15 16 17 18 19 20 20
21 22 23 24 25 26 27 28 29 30 30
31 32 33 34 35 36 37 38 39 40 40
41 42 43 44 45 46 47 48 49 50 50
51 52 53 54 55 56 57 58 59 60 60
61 62 63 64 65 66 67 68 69 70 70
71 72 73 74 75 76 77 78 79 80 80
81 82 83 84 85 86 87 88 89 90 90
91 92 93 94 95 96 97 98 99 100 100
2.15.4.Insert line separator
|
Public Class Tester
Public Shared Sub Main
Dim result As New System.Text.StringBuilder
result.AppendLine("A")
result.AppendLine("B")
result.AppendLine("C")
result.AppendLine("D")
result.Append("E")
Dim resultAsString As String = result.ToString()
Console.WriteLine(resultAsString)
resultAsString = InsertLine(resultAsString, 3, "(inserted)")
Console.WriteLine(resultAsString)
End Sub
Public Shared Function InsertLine(ByVal source As String, _
ByVal lineNum As Integer, _
ByVal lineToInsert As String) As String
Dim lineSet() As String
Dim atLine As Integer
lineSet = Split(source, vbNewLine)
atLine = lineNum
If (atLine < 0) Then atLine = 0
If (atLine >= lineSet.Length) Then
lineSet(lineSet.Length - 1) &= vbNewLine & lineToInsert
Else
lineSet(atLine) = _
lineToInsert & vbNewLine & lineSet(atLine)
End If
Return Join(lineSet, vbNewLine)
End Function
End Class
|
A
B
C
D
E
A
B
C
(inserted)
D
E
2.16.Boolean
2.16.1.Define Boolean value and use it
in If statement
|
public class Test
public Shared Sub Main
Dim blnStatus As Boolean = True
Console.WriteLine(blnStatus)
blnStatus = Not blnStatus
Console.WriteLine(blnStatus)
If blnStatus Then
Console.WriteLine("The status is true.")
Else
Console.WriteLine("The status is false.")
End If
End Sub
End class
|
True
False
The status is false.
2.16.2.Boolean value calculation: Or, Xor, And, Not
|
public class Test
public Shared Sub Main
Dim B As Boolean
B = False Or True
Console.WriteLine(B)
B = False Xor False
Console.WriteLine(B)
B = False And True
Console.WriteLine(B)
B = Not True
Console.WriteLine(B)
End Sub
End class
|
True
False
False
False
2.16.3.CBool: convert Integer to Boolean
|
Module Tester
Public Sub Main()
Dim iBoolean As Integer = -1
Dim bBoolean As Boolean = CBool(iBoolean)
Console.WriteLine("Boolean of {0} is {1}", iBoolean, bBoolean)
End Sub
End Module
|
Boolean of -1 is True
2.16.4.CBool(0): convert 0 to Boolean
|
Module Tester
Public Sub Main()
Dim iBoolean As Integer = -1
Dim bBoolean As Boolean = CBool(iBoolean)
bBoolean = CBool(0)
Console.WriteLine("Boolean of 0 is {0}", bBoolean)
End Sub
End Module
|
Boolean of 0 is False
2.17.Hex
|
Public Class Tester
Public Shared Sub Main
For counter As Integer = 0 To 15
Console.WriteLine(Hex(counter))
Next counter
End Sub
End Class
|
0
1
2
3
4
5
6
7
8
9
A
B
C
D
E
F
2.17.2.Hex: output hexadecimal value
|
Option Strict On
Public Module modMain
Public Sub Main()
Console.WriteLine(Hex("&HE0F1"))
Console.WriteLine(Hex("&HFFFF"))
End Sub
End Module
|
E0F1
FFFF
2.17.3.Create a string value that has four hexadecimal digits.
|
Module Example
Public Sub Main()
Dim byteValues() As Byte = { 12, 163, 255 }
For Each byteValue As Byte In byteValues
Console.WriteLine(byteValue.ToString("X4"))
Next
End Sub
End Module
|
2.18.Bit
2.18.1.Bit Shift left and right
|
public class Test
public Shared Sub Main
'&HFF = the hex value FF, which equals 255, and
'1111 1111 in binary
Dim numberToBeShifted As Integer = &HFF
numberToBeShifted = numberToBeShifted << 4
Console.WriteLine(numberToBeShifted)
numberToBeShifted >>= 2
Console.WriteLine(numberToBeShifted)
End Sub
End class
|
4080
1020
2.18.2.Sign Bit
|
Option Strict On
Public Module SignBit
Public Sub Main()
Dim negValue As Integer = -1024
' Save state of sign bit
Dim signBit As Integer = negValue And &H80000000
negValue = negValue << 2
' Clear sign bit
negValue = negValue And &H7FFFFFFF
' Restore sign bit
negValue = negValue Or signBit
Console.WriteLine("Value after shift operation: {0}", negValue)
End Sub
End Module
|
Value after shift operation: -4096
2.19.Complex Number
2.19.1.Complex
|
public class Test
public Shared Sub Main
Dim X, Y As Complex
X = New Complex(1, 4)
Y = New Complex(2, 3)
Console.WriteLine((X + Y).ToString)
Console.WriteLine((X - Y).ToString)
Console.WriteLine((X * Y).ToString)
Console.WriteLine((X = Y).ToString)
Console.WriteLine((X <> Y).ToString)
Console.WriteLine((-X).ToString)
Dim abs_x As Double = CDbl(X)
Console.WriteLine(abs_x.ToString)
End Sub
End class
Public Class Complex
Public Re As Double
Public Im As Double
Public Sub New()
End Sub
Public Sub New(ByVal real_part As Double, ByVal imaginary_part As Double)
Re = real_part
Im = imaginary_part
End Sub
Public Overrides Function ToString() As String
Return Re.ToString & " + " & Im.ToString & "i"
End Function
Public Shared Operator *(ByVal c1 As Complex, ByVal c2 As Complex) As Complex
Return New Complex( _
c1.Re * c2.Re - c1.Im * c2.Im, _
c1.Re * c2.Im + c1.Im * c2.Re)
End Operator
Public Shared Operator +(ByVal c1 As Complex, ByVal c2 As Complex) As Complex
Return New Complex( c1.Re + c2.Re,c1.Im + c2.Im)
End Operator
Public Shared Operator -(ByVal c1 As Complex, ByVal c2 As Complex) As Complex
Return New Complex(c1.Re - c2.Re, c1.Im - c2.Im)
End Operator
Public Shared Operator =(ByVal c1 As Complex, ByVal c2 As Complex) As Boolean
Return (c1.Re = c2.Re) AndAlso (c1.Im = c2.Im)
End Operator
Public Shared Operator <>(ByVal c1 As Complex, ByVal c2 As Complex) As Boolean
Return (c1.Re <> c2.Re) OrElse (c1.Im <> c2.Im)
End Operator
Public Shared Operator -(ByVal c1 As Complex) As Complex
Return New Complex(c1.Im, c1.Re)
End Operator
Public Shared Narrowing Operator CType(ByVal c1 As Complex) As Double
Return System.Math.Sqrt(c1.Re * c1.Re + c1.Im * c1.Im)
End Operator
End Class
|
3 + 7i
-1 + 1i
-10 + 11i
False
True
4 + 1i
4.12310562561766
2.19.2.Complex Number
|
Public Class Tester
Public Shared Sub Main
Dim result As New System.Text.StringBuilder
Dim a As ComplexNumber
Dim b As ComplexNumber
Dim c As ComplexNumber
a = New ComplexNumber(3, 4)
b = New ComplexNumber(5, -2)
c = a + b
result.AppendLine("Complex Numbers")
result.AppendLine("a = " & a.ToString())
result.AppendLine("b = " & b.ToString())
' ----- Addition.
c = a + b
result.AppendLine("a + b = " & c.ToString())
' ----- Subtraction.
c = a - b
result.AppendLine("a - b = " & c.ToString())
' ----- Multiplication.
c = a * b
result.AppendLine("a * b = " & c.ToString())
' ----- Division.
c = a / b
result.AppendLine("a / b = " & c.ToString())
' ----- Addition as assignment.
a += b
result.AppendLine("a += b ... a = " & a.ToString())
Console.WriteLine(result.ToString())
End Sub
End Class
Structure ComplexNumber
Public Real As Double
Public Imaginary As Double
Public Sub New(ByVal realPart As Double, ByVal imaginaryPart As Double)
Me.Real = realPart
Me.Imaginary = imaginaryPart
End Sub
Public Sub New(ByVal sourceNumber As ComplexNumber)
Me.Real = sourceNumber.Real
Me.Imaginary = sourceNumber.Imaginary
End Sub
Public Overrides Function ToString() As String
Return Real & "+" & Imaginary & "i"
End Function
Public Shared Operator +(ByVal a As ComplexNumber, _
ByVal b As ComplexNumber) As ComplexNumber
Return New ComplexNumber(a.Real + b.Real, a.Imaginary + b.Imaginary)
End Operator
Public Shared Operator -(ByVal a As ComplexNumber, _
ByVal b As ComplexNumber) As ComplexNumber
Return New ComplexNumber(a.Real - b.Real, a.Imaginary - b.Imaginary)
End Operator
Public Shared Operator *(ByVal a As ComplexNumber, _
ByVal b As ComplexNumber) As ComplexNumber
Return New ComplexNumber(a.Real * b.Real - a.Imaginary * b.Imaginary, _
a.Real * b.Imaginary + a.Imaginary * b.Real)
End Operator
Public Shared Operator /(ByVal a As ComplexNumber, _
ByVal b As ComplexNumber) As ComplexNumber
Return a * Reciprocal(b)
End Operator
Public Shared Function Reciprocal(ByVal a As ComplexNumber) As ComplexNumber
Dim divisor As Double
divisor = a.Real * a.Real + a.Imaginary * a.Imaginary
If (divisor = 0.0#) Then Throw New DivideByZeroException
Return New ComplexNumber(a.Real / divisor, -a.Imaginary / divisor)
End Function
End Structure
|
Complex Numbers
a = 3+4i
b = 5+-2i
a + b = 8+2i
a - b = -2+6i
a * b = 23+14i
a / b = 0.241379310344828+0.896551724137931i
a += b ... a = 8+2i
2.20.Enum
2.20.1.Define Enum and assign value
|
Module Module1
Enum Temperatures
A = 0
B = 32
C = 60
D = 72
E = 212
End Enum
Sub Main( )
System.Console.WriteLine("B: {0}",Temperatures.B)
System.Console.WriteLine("E: {0}",Temperatures.E)
End Sub
End Module
|
B: B
E: E
2.20.2.Define and use Enum as Integer
|
Option Strict On
<Flags> Public Enum MyValues As Integer
AA = 1
BB = 2
CC = 4
DD = 8
End Enum
Public Module modMain
Public Sub Main()
Dim Computer1 As MyValues = MyValues.AA Or MyValues.BB
Console.WriteLine(Computer1.ToString())
End Sub
End Module
|
AA, BB
2.20.3.Declare Enum variable
|
Public Enum AccessLevel
Clerk
Supervisor
Administrator
End Enum
public class Test
public Shared Sub Main
Dim m_AccessLevel As AccessLevel
m_AccessLevel = AccessLevel.Supervisor
End Sub
End class
|
2.20.4.Public Enum type
|
Imports System
Module HelloWorld
Public Enum CreditCard
Visa
MasterCard
AmericanExpress
Discover
End Enum
Public Sub Main()
Dim cc as CreditCard
cc = CreditCard.Visa
Console.WriteLine(cc)
End Sub
End Module
|
2.20.5.Assign value to Enum elements
|
Public Enum AccessLevel
Clerk = 10
Supervisor
Administrator = -1
End Enum
public class Test
public Shared Sub Main
Dim m_AccessLevel As AccessLevel
m_AccessLevel = AccessLevel.Supervisor
End Sub
End class
|
2.20.6.Assign value to only one Enum
element
|
Public Enum AccessLevel
Clerk
Supervisor
Administrator
User = 0
Manager
SysAdmin
Superuser = SysAdmin
End Enum
public class Test
public Shared Sub Main
Dim m_AccessLevel As AccessLevel
m_AccessLevel = AccessLevel.Supervisor
End Sub
End class
|
2.20.7.Cast Integer to Enum value
|
Public Enum AccessLevel
Clerk
Supervisor
Administrator
User = 0
Manager
SysAdmin
Superuser = SysAdmin
End Enum
public class Test
public Shared Sub Main
Dim m_AccessLevel As AccessLevel
Dim integer_value As Integer = 1
m_AccessLevel = CType(integer_value, AccessLevel)
Dim access_level As AccessLevel = AccessLevel.Clerk
Console.WriteLine(access_level.ToString())
End Sub
End class
|
2.20.8.Convert Enum to Integer
|
Module Module1
Enum Temperatures
A = 0
B = 32
C = 60
D = 72
E = 212
End Enum
Sub Main( )
System.Console.WriteLine("B: {0}",CInt(Temperatures.B))
System.Console.WriteLine("E: {0}", CInt(Temperatures.E))
End Sub
End Module
|
B: 32
E: 212
2.20.9.Enum value duplication
|
Public Enum AccessLevel
Level1
Level2
Level3
AliasLevel1 = Level1
AliasLevel2 = Level2
AliasLevel3 = Level3
AliasLevel4 = Level3
End Enum
public class Test
public Shared Sub Main
Dim access_level As AccessLevel = AccessLevel.Level1
Console.WriteLine(access_level.ToString())
Console.WriteLine(AccessLevel.Level1.ToString())
Console.WriteLine(AccessLevel.Level2.ToString())
Console.WriteLine(AccessLevel.Level3.ToString())
End Sub
End class
|
Level1
Level1
Level2
AliasLevel3
2.20.10.Compare Enum element using logic operator
|
Public Enum workDays
Saturday
Sunday = 0
Monday
Tuesday
Wednesday
Thursday
Friday
invalid = -1
End Enum
Public Class Tester
Public Shared Sub Main
Dim MyDay As WorkDays
MyDay = WorkDays.Saturday
If MyDay < workDays.FriDay Then
Console.WriteLine("It's the weekend.Invalid work day!")
End If
End Sub
End Class
|
It's the weekend.Invalid work day!
2.20.11.Converting an enumerated value to a string.
|
Imports System
Public Class EnumSample
Enum Colors
Red = 1
Blue = 2
End Enum
Public Shared Sub Main()
Dim myColors As Colors = Colors.Red
Console.WriteLine("The value of this instance is '{0}'",myColors.ToString())
End Sub
End Class
|
2.20.12.Standard Enumeration Format
Specifiers
|
Imports System
Imports Microsoft.VisualBasic
Class Sample
Public Enum Color
Yellow = 1
Blue = 2
Green = 3
End Enum 'Color
Public Shared Sub Main()
' Format a Color enumeration value in various ways.
Console.WriteLine("Standard Enumeration Format Specifiers")
Console.WriteLine("(G) General:. . . . . . . . . {0:G}" & vbCrLf & _
" (default):. . . . . . . . {0} (default = 'G')" & vbCrLf & _
"(F) Flags:. . . . . . . . . . {0:F} (flags or integer)" & vbCrLf & _
"(D) Decimal number: . . . . . {0:D}" & vbCrLf & _
"(X) Hexadecimal:. . . . . . . {0:X}" & vbCrLf, _
Color.Green)
End Sub
End Class
|
2.21.Overflows
2.21.1.Demonstrating overflows with and
without checking
|
Class Tester
Shared Sub Main()
Try
Dim number1 As Integer = Int32.MaxValue ' 2,147,483,647
Dim number2 As Integer = Int32.MaxValue ' 2,147,483,647
Dim sum As Integer = 0
Console.WriteLine("number1: {0}" & vbCrLf & _
"number2: {1}", number1, number2)
Console.WriteLine("Sum integers in checked context:")
sum = number1 + number2 ' compute sum
Console.WriteLine("Sum after operation: {0}", sum)
Catch overflowExceptionParameter As OverflowException
Console.WriteLine(overflowExceptionParameter.ToString())
End Try
End Sub
End Class
|
number1: 2147483647
number2: 2147483647
Sum integers in checked context:
System.OverflowException: Arithmetic operation resulted in an overflow.
at Tester.Main()
2.22.Numeric format
2.22.1.Numeric format: {0:N}, {1:E} and
G5
|
Public Class Tester
Public Shared Sub Main
Dim intValue As Integer = 1234567
Dim floatValue As Double = Math.PI
Dim result As New System.Text.StringBuilder
result.AppendLine(String.Format("{0} ... {1}", _
intValue, floatValue))
result.AppendLine(String.Format("{0:N} ... {1:E}", _
intValue, floatValue))
result.AppendLine(intValue.ToString("N5") & " ... " & _
floatValue.ToString("G5"))
Console.WriteLine(result.ToString())
End Sub
End Class
|
1234567 ... 3.14159265358979
1,234,567.00 ... 3.141593E+000
1,234,567.00000 ... 3.1416
2.23.Boxing unboxing
2.23.1.Boxing and unboxing Integer
|
Option Strict On
Imports System
Public Class UnboxingTest
Public Shared Sub Main( )
Dim myIntegerVariable As Integer = 123
' Boxing
Dim myObjectVariable As Object = myIntegerVariable
Console.WriteLine("myObjectVariable: {0}",myObjectVariable.ToString( ))
' unboxing (must be explicit)
Dim anotherIntegerVariable As Integer = DirectCast(myObjectVariable, Integer)
Console.WriteLine("anotherIntegerVariable: {0}",anotherIntegerVariable)
End Sub
End Class
|
myObjectVariable: 123
anotherIntegerVariable: 123
2.24.Cast
2.24.1.Implicit casting of quotient to
an integer
|
Option Strict Off
' must be off to allow implicit casting of quotient to an integer
Imports System
Module Module1
Sub Main( )
Dim twelve As Integer = 12
Dim five As Integer = 5
Dim intAnswer As Integer
Dim doubleAnswer As Double
Console.WriteLine("{0} + {1} = {2}",twelve, five, twelve + five)
Console.WriteLine("{0} - {1} = {2}",twelve, five, twelve - five)
Console.WriteLine("{0} * {1} = {2}",twelve, five, twelve * five)
' integer division
intAnswer = twelve \ five
doubleAnswer = twelve \ five
Console.WriteLine("{0} \ {1} = [integer] {2} [double] {3}", _
twelve, five, intAnswer, doubleAnswer)
' division. Assign result to both an integer and a double
' note, option strict must be off!
intAnswer = twelve / five
doubleAnswer = twelve / five
Console.WriteLine("{0} / {1} = [integer] {2} [double] {3}", _
twelve, five, intAnswer, doubleAnswer)
End Sub
End Module
|
12 + 5 = 17
12 - 5 = 7
12 * 5 = 60
12 \ 5 = [integer] 2 [double] 2
12 / 5 = [integer] 2 [double] 2.4
2.25.CType
2.25.1.Use CType to convert from
derived class to base class
|
public class Test
public Shared Sub Main
Dim people As New Collection
people.Add(New Employee("A"))
people.Add(New Customer("B"))
Dim emp As Employee
For Each person As Object In people
If TypeOf person Is Employee Then
emp = CType(person, Employee)
Console.WriteLine(emp.Name)
ElseIf TypeOf person Is Customer Then
Console.WriteLine(CType(person, Customer).Name)
End If
Next person
End Sub
End class
Public Class Employee
Public Name As String
Public Sub New(ByVal new_name As String)
Name = new_name
End Sub
Public Overridable Function IsManager() As Boolean
Return False
End Function
End Class
Public Class Customer
Public Name As String
Public Sub New(ByVal new_name As String)
Name = new_name
End Sub
End Class
Public Class Manager
Inherits Employee
Public Sub New(ByVal new_name As String)
MyBase.new(new_name)
End Sub
Public Overrides Function IsManager() As Boolean
Return True
End Function
End Class
|
A
B
2.26.String
2.26.1.Declare String Variable and
assign value
|
Module Module1
Sub Main()
Dim EmployeeName As String
Dim EmployeePhoneNumber As String
Dim EmployeeSalary As Double
Dim NumberOfEmployees As Integer
EmployeeName = "James Bond"
EmployeePhoneNumber = "555-1212"
EmployeeSalary = 45.0
NumberOfEmployees = 1
Console.WriteLine("Number of employees: " & NumberOfEmployees)
Console.WriteLine("Employee name: " & EmployeeName)
Console.WriteLine("Employee phone number: " & EmployeePhoneNumber)
Console.WriteLine("Employee salary: " & EmployeeSalary)
End Sub
End Module
|
Number of employees: 1
Employee name: James Bond
Employee phone number: 555-1212
Employee salary: 45
2.26.2.String.Empty
|
Option Strict On
Public Module modMain
Public Sub Main()
Console.WriteLine(String.Empty)
End Sub
End Module
|
2.26.3.Demonstrating String class
constructors
|
Module Tester
Sub Main()
Dim characterArray As Char()
Dim quotes As Char = ChrW(34)
Dim originalString, string1, string2, string3, string4 As String
characterArray = New Char() {"A"c, "B"c, "C"c, "D"c, "E"c, "F"c, " "c, "G"c, "H"c}
originalString = "test"
string1 = originalString
string2 = New String(characterArray)
string3 = New String(characterArray, 6, 3)
string4 = New String("C"c, 5)
Console.WriteLine(string1)
Console.WriteLine("string2 = " & string2 )
Console.WriteLine("string3 = " & string3 )
Console.WriteLine("string4 = " & string4 )
End Sub ' Main
End Module
|
test
string2 = ABCDEF GH
string3 = GH
string4 = CCCCC
2.26.4.Join string
|
Imports System.Collections
public class Test
public Shared Sub Main
Dim s() As String = {"one", "two", "three"} 'a string array
Dim s2 As String
s2 = s2.Join(", ", s)
Console.WriteLine(s2)
End Sub
End class
|
one, two, three
2.26.5.Copy characters from string1 into character Array
|
Module Tester
Sub Main()
Dim string1 As String
Dim characterArray As Char()
Dim i As Integer
Dim quotes As Char = ChrW(34)
string1 = "hello there"
characterArray = New Char(5) {}
string1.CopyTo(0, characterArray, 0, 5)
For i = 0 To characterArray.GetUpperBound(0)
Console.WriteLine(characterArray(i))
Next
End Sub ' Main
End Module
|
h
e
l
l
o
2.26.6.String Length property
|
Module Tester
Sub Main()
Dim string1 As String
Dim characterArray As Char()
Dim i As Integer
Dim quotes As Char = ChrW(34)
string1 = "hello there"
characterArray = New Char(5) {}
Console.WriteLine("Length of string1: " & string1.Length)
End Sub ' Main
End Module
|
Length of string1: 11
2.26.7.Demonstrating method GetHashCode of class String
|
Module Tester
Sub Main()
Dim string1 As String = "hello"
Dim string2 As String = "Hello"
Console.WriteLine(string1.GetHashCode() )
Console.WriteLine(string2.GetHashCode())
End Sub ' Main
End Module
|
-695839
-694847
2.26.8.Insert sub string by index
|
Option Strict On
Imports System
Class Tester
Public Shared Sub Main( )
Dim s1 As String = "abcd"
Dim s2 As String = "ABCD"
Dim s3 As String = "AAAAs "
s3 = s3 & "development"
Dim s5 As String = String.Copy(s2) '
Console.WriteLine("s5 copied from s2: {0}", s5)
Console.WriteLine("String s3 is {0} characters long. ",s5.Length)
Console.WriteLine("s3: {0}", s3)
' hold the location of provides as an integer
Dim location As Integer = s3.IndexOf("a")
Dim s10 As String = s3.Insert(location, "u")
Console.WriteLine("s10: {0}", s10)
End Sub 'Main
End Class 'Tester
|
s5 copied from s2: ABCD
String s3 is 4 characters long.
s3: AAAAs development
Unhandled Exception: System.ArgumentOutOfRangeException: Index was out of range. Must be non-negativ
e and less than the size of the collection.
Parameter name: startIndex
at System.String.Insert(Int32 startIndex, String value)
at Tester.Main()
2.26.9.Insert method returns the resulting string
|
public class Test
public Shared Sub Main
Dim s1 As New String("Greeting")
s1.Insert(4, "sdss") 'DOES NOT CHANGE S1!!!!
s1 = s1.Insert(8, "s") 'changes Greeting to Greetings
Console.WriteLine(s1.Length)
Console.WriteLine(s1)
End Sub
End class
|
9
Greetings
2.26.10.SubString
|
Option Strict On
Imports System
Class Tester
Public Shared Sub Main( )
Dim s1 As String = "One Two Three Four"
Dim index As Integer
index = s1.LastIndexOf(" ")
Dim s2 As String = s1.Substring((index + 1))
s1 = s1.Substring(0, index)
index = s1.LastIndexOf(" ")
Dim s3 As String = s1.Substring((index + 1))
s1 = s1.Substring(0, index)
index = s1.LastIndexOf(" ")
Dim s4 As String = s1.Substring((index + 1))
s1 = s1.Substring(0, index)
index = s1.LastIndexOf(" ")
Dim s5 As String = s1.Substring((index + 1))
Console.WriteLine("s1: {0}", s1)
Console.WriteLine("s2: {0}", s2)
Console.WriteLine("s3: {0}", s3)
Console.WriteLine("s4: {0}", s4)
Console.WriteLine("s5: {0}", s5)
End Sub 'Main
End Class 'Tester
|
s1: One
s2: Four
s3: Three
s4: Two
s5: One
2.26.11.Get string morse code
|
Public Class Tester
Public Shared Sub Main
Dim source As String = "Hello world!"
Dim characters As String = _
"~ABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789.,:?'-/"""
Dim morse() As String = { _
"?", ".-", "-...", "-.-.", "-..", ".", "..-.", "--.", "....", _
"..", ".---", "-.-", ".-..", "--", "-.", "---", ".--.", _
"--.-", ".-.", "...", "-", "..-", "...-", ".--", "-..-", _
"-.--", "--..", "-----", ".----", "..---", "...--", _
"....-", ".....", "-....", "--...", "---..", "----.", _
".-.-.-", "--..--", "---...", "..--..", ".----.", _
"-....-", "-..-.", ".-..-."}
Dim counter As Integer
Dim position As Integer
For counter = 0 To source.Length - 1
position = characters.IndexOf(Char.ToUpper( _
source.Chars(counter)))
If (position < 0) Then position = 0
Console.Write (source.Substring(counter, 1) & " ")
Console.WriteLine(morse(position))
Next counter
End Sub
End Class
|
H ....
e .
l .-..
l .-..
o ---
?
w .--
o ---
r .-.
l .-..
d -..
! ?
2.26.12.String operation timing
|
Public Class Tester
Public Shared Sub Main
Dim content As String = ""
Dim result As New System.Text.StringBuilder
Dim counter As Integer
Dim dateTime1 As Date
Dim dateTime2 As Date
Dim dateTime3 As Date
Dim loopCount As Integer = 15000
dateTime1 = Now
For counter = 1 To loopCount
content &= counter.ToString()
Next counter
dateTime2 = Now
For counter = 1 To loopCount
result.Append(counter.ToString())
Next counter
dateTime3 = Now
content = String.Format( _
"First loop took {0:G4} ms, the second took {1:G4} ms.", _
dateTime2.Subtract(dateTime1).TotalMilliseconds, _
dateTime3.Subtract(dateTime2).TotalMilliseconds)
Console.WriteLine(content)
End Sub
End Class
|
First loop took 1734 ms, the second took 0 ms.
2.26.13.Change tab to space
|
Public Class Tester
Public Shared Sub Main
Dim tabs As String = "This~is~~a~tabbed~~~string".Replace("~"c, vbTab)
Dim spaces As String = TabsToSpaces(tabs, 8)
Dim periods As String = spaces.Replace(" "c, "."c)
Console.WriteLine(tabs)
Console.WriteLine(spaces)
Console.WriteLine(periods)
End Sub
Public Shared Function TabsToSpaces(ByVal source As String, ByVal tabSize As Integer) As String
Dim result As New System.Text.StringBuilder
Dim counter As Integer
For counter = 0 To source.Length - 1
If (source.Chars(counter) = vbTab) Then
Do
result.Append(Space(1))
Loop Until ((result.Length Mod tabSize) = 0)
Else
result.Append(source.Chars(counter))
End If
Next counter
Return result.ToString()
End Function
End Class
|
This is a tabbed string
This is a tabbed string
This....is..............a.......tabbed..................string
2.26.14.ToString
|
Public Class Tester
Public Shared Sub Main
Dim someInt As Integer = 123
Dim someDouble As Double = Math.PI
Dim someString As String = "Testing"
Dim someDate As Date = #7/4/1776 9:10:11 AM#
Dim someDecimal As Decimal = 1D / 3D
Dim result As New System.Text.StringBuilder
result.Append("someInt.ToString ")
result.AppendLine(someInt.ToString())
result.Append("someDouble.ToString ")
result.AppendLine(someDouble.ToString())
result.Append("someString.ToString ")
result.AppendLine(someString.ToString())
result.Append("someDate.ToString ")
result.AppendLine(someDate.ToString())
result.Append("someDecimal.ToString ")
result.Append(someDecimal.ToString())
Console.WriteLine(result.ToString())
End Sub
End Class
|
someInt.ToString 123
someDouble.ToString 3.14159265358979
someString.ToString Testing
someDate.ToString 04/07/1776 9:10:11 AM
someDecimal.ToString 0.3333333333333333333333333333
2.26.15.Catch Exception for String.Substring
|
public class Test
public Shared Sub Main
Dim strCaption As String
strCaption = "Answer"
Try
Console.WriteLine(strCaption.Substring(10, 1))
Catch ex As Exception
Console.WriteLine(ex.Message)
End Try
End Sub
End class
|
startIndex cannot be larger than length of string.
Parameter name: startIndex
2.26.16.Count Vowels
|
Imports System.IO
public class Test
public Shared Sub Main
Console.WriteLine("VOWELS COUNTED: " & CountTheVowels("asdffdsaasdf"))
End Sub
Private Shared Function CountTheVowels(ByVal strSomeString As String) As Integer
Dim intCount As Integer = 1
Dim intTotal As Integer = 0
Dim intPosition As Integer
'Loop through the string and count the vowels.
Do While intCount <= strSomeString.Length
intPosition = InStr("aeio", strSomeString.Substring(intCount, 1).ToLower)
If intPosition > 0 Then
intTotal += 1
End If
Loop
Return intTotal
End Function
End class
|
2.26.17.Reverse a string
|
public class Test
public Shared Sub Main
Dim objTS As TimeSpan
Dim dteStart As Date
Dim strText As String
Dim strChar As String
Dim intChar As Integer
dteStart = Now()
strText = "12345678"
Dim intLen As Integer = Len(strText)
For intChar = 1 To CInt(intLen / 2)
strChar = Mid(strText, intChar, 1)
Mid(strText, intChar, 1) = Mid(strText, intLen - intChar - 1, 1)
Mid(strText, intLen - intChar - 1) = strChar
Next
objTS = Now().Subtract(dteStart)
Console.WriteLine(objTS.ToString)
Console.WriteLine(strText)
End Sub
End class
|
00:00:00
65342178
2.26.18.Make a reference copy
|
Public Class Tester
Public Shared Sub Main
Dim arrayA() As String = {"One", "Two", "Three", "Four", "Five", "Six"}
Console.WriteLine(Join(arrayA, ","))
Dim arrayB() As String = {"A", "B", "C", "D", "E", "E", "F", "G", "H"}
Console.WriteLine(Join(arrayB, ","))
' ----- Make a reference copy.
Dim arrayC() As String = arrayA
Console.WriteLine(Join(arrayC, ","))
End Sub
End Class
|
One,Two,Three,Four,Five,Six
A,B,C,D,E,E,F,G,H
One,Two,Three,Four,Five,Six
2.26.19.Check a Credit card number
|
' Quote from
'Visual Basic 2005 Cookbook Solutions for VB 2005 Programmers
'by Tim Patrick (Author), John Craig (Author)
'# Publisher: O'Reilly Media, Inc. (September 21, 2006)
'# Language: English
'# ISBN-10: 0596101775
'# ISBN-13: 978-0596101770
Public Class Tester
Public Shared Sub Main
Console.WriteLine(VerifyCreditCard("123123123123123123"))
End Sub
Private Shared Function VerifyCreditCard(ByVal cardNumber As String) As Boolean
' ----- Given a card number, make sure it is valid. This method
' uses the Luhn algorithm to verify the number. This routine
' assumes that cardNumber contains only digits.
Dim counter As Integer
Dim digitTotal As Integer
Dim holdValue As Integer
Dim checkDigit As Integer
Dim calcDigit As Integer
Dim useCard As String
' ----- Perform some initial checks.
useCard = Trim(cardNumber)
If (IsNumeric(useCard) = False) Then Return False
' ----- Separate out the last digit, the check digit. For cards with
' an odd number of digits, prepend with a zero.
If ((Len(useCard) Mod 2) <> 0) Then useCard = "0" & useCard
checkDigit = useCard.Substring(Len(useCard) - 1, 1)
useCard = useCard.Substring(0, Len(useCard) - 1)
' ----- Process each digit.
digitTotal = 0
For counter = 1 To Len(useCard)
If ((counter Mod 2) = 1) Then
' ----- This is an odd digit position. Double the number.
holdValue = CInt(Mid(useCard, counter, 1)) * 2
If (holdValue > 9) Then
' ----- Break the digits (e.g., 19 becomes 1+9).
digitTotal += (holdValue \ 10) + (holdValue - 10)
Else
digitTotal += holdValue
End If
Else
' ----- This is an even digit position. Simply add it.
digitTotal += CInt(Mid(useCard, counter, 1))
End If
Next counter
' ----- Calculate the 10's complement of both values.
calcDigit = 10 - (digitTotal Mod 10)
If (calcDigit = 10) Then calcDigit = 0
If (checkDigit = calcDigit) Then Return True Else Return False
End Function
End Class
|
False
2.26.20.Read String value from Keyboard
|
Module Module1
Sub Main()
Dim FirstName As String
Console.Write("Name: ")
FirstName = Console.ReadLine()
Console.WriteLine(FirstName)
End Sub
End Module
|
Name: name
name
2.27.String Concatenate
2.27.1.String Concatenate
|
Option Strict On
Imports System
Class Tester
Public Shared Sub Main( )
Dim s1 As String = "abcd"
Dim s2 As String = "ABCD"
' concatenation method
Dim s3 As String = String.Concat(s1, s2)
Console.WriteLine("s3 concatenated from s1 and s2: {0}", s3)
End Sub 'Main
End Class 'Tester
|
s3 concatenated from s1 and s2: abcdABCD
2.27.2.Use the overloaded operator
|
Option Strict On
Imports System
Class Tester
Public Shared Sub Main( )
Dim s1 As String = "abcd"
Dim s2 As String = "ABCD"
Dim s4 As String = s1 & s2
Console.WriteLine("s4 concatenated from s1 & s2:"+ s4)
End Sub 'Main
End Class 'Tester
|
s4 concatenated from s1 & s2: abcdABCD
2.27.3.Create Random String from String array
|
Imports System.Collections
Module Example
Public Sub Main()
Const WORD_SIZE As Integer = 4
Dim words() As String = { "1234", "5678", "90qw", "qwer" }
Dim keys(WORD_SIZE) As Double
Dim letters(WORD_SIZE) As String
Dim rnd As New Random()
For Each word As String In words
For ctr As Integer = 0 To word.Length - 1
keys(ctr) = rnd.NextDouble()
letters(ctr) = word.Chars(ctr)
Next
Array.Sort(keys, letters, 0, WORD_SIZE, Comparer.Default)
Dim scrambledWord As String = String.Concat(letters(0), letters(1), letters(2), letters(3))
Console.WriteLine(word)
Console.WriteLine(scrambledWord)
Next
End Sub
End Module
|
2.27.4.Concat method with a String
array.
|
Imports System
Public Class ConcatTest
Public Shared Sub Main()
Dim s As String() = {"hello ", "and ", "welcome ", "to ", "this ", "demo! "}
Console.WriteLine(String.Concat(s))
Array.Sort(s)
Console.WriteLine(String.Concat(s))
End Sub
End Class
|
2.28.String and Byte Char Array
2.28.1.Convert String to Char using
System.Convert.ToChar
|
Imports System.Collections
public class ConvertToChar
public Shared Sub Main
Dim c As Char
c = System.Convert.ToChar("A")
Console.WriteLine(c)
End Sub
End class
|
A
2.28.2.ToCharArray methods
|
Imports System.Text
Module Tester
Sub Main()
Dim string1 As String = "hello"
Dim i As Integer
Dim charArray() As Char = string1.ToCharArray()
' display contents of charArray
For i = 0 To charArray.Length - 1
Console.WriteLine(charArray(i))
Next
End Sub ' Main
End Module
|
h
e
l
l
o
2.28.3.Strings And Byte Arrays
|
Public Class Tester
Public Shared Sub Main
Dim quote As String = "AAAAAasdfasdfasdfasdfasdfasdfasdfadsfasdfadsfads"
Dim bytes() As Byte
' ----- Assumed to be all ASCII character.
bytes = System.Text.Encoding.UTF8.GetBytes(quote)
bytes(46) = 33 ' ASCII exclamation point
Console.WriteLine(System.Text.Encoding.UTF8.GetString(bytes))
' ----- Works with all character sets.
bytes = System.Text.Encoding.Unicode.GetBytes(quote)
bytes(92) = 63 ' ASCII question mark
bytes(93) = 0
Console.WriteLine(System.Text.Encoding.Unicode.GetString(bytes))
End Sub
End Class
|
AAAAAasdfasdfasdfasdfasdfasdfasdfadsfasdfadsfa!s
AAAAAasdfasdfasdfasdfasdfasdfasdfadsfasdfadsfa?s
2.28.4.String and char array
|
Public Class Tester
Public Shared Sub Main
Dim quote As String = "aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa"
Dim charArray() As Char = CType(quote, Char())
charArray(6) = "!"c
Dim result As String = New String(charArray)
Console.WriteLine(result)
End Sub
End Class
|
aaaaaa!aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa
2.28.5.Reorder chars in a string
|
Public Class Tester
Public Shared Sub Main
Dim counter As Integer
Dim position As Integer
Dim holdChar As Char
Dim jumbleMethod As New Random
Dim quote As String = "abcedfg"
Dim chars() As Char = CType(quote, Char())
For counter = 0 To chars.Length - 1
position = jumbleMethod.Next Mod chars.Length
holdChar = chars(counter)
chars(counter) = chars(position)
chars(position) = holdChar
Next counter
Dim result As String = New String(chars)
Console.WriteLine(result)
End Sub
End Class
|
cfabdge
2.28.6.Loop through characters in string and display reversed
|
Module Tester
Sub Main()
Dim string1 As String
Dim characterArray As Char()
Dim i As Integer
Dim quotes As Char = ChrW(34)
string1 = "hello there"
characterArray = New Char(5) {}
For i = string1.Length - 1 To 0 Step -1
Console.WriteLine(string1.Chars(i))
Next
End Sub ' Main
End Module
|
e
r
e
h
t
o
l
l
e
h
2.28.7.Use IndexOf to locate a character in a string
|
Module Tester
Sub Main()
Dim letters As String = "abcdefghijklmabcdefghijklm"
Dim searchLetters As Char() = New Char() {"c"c, "a"c, "$"c}
Console.WriteLine(letters.IndexOf("c"c))
Console.WriteLine(letters.IndexOf("a"c, 1))
Console.WriteLine(letters.IndexOf("$"c, 3, 5))
End Sub ' Main
End Module ' modIndexMethods
|
2
13
-1
2.28.8.Use LastIndexOf to find a character in a string
|
Module Tester
Sub Main()
Dim letters As String = "abcdefghijklmabcdefghijklm"
Dim searchLetters As Char() = New Char() {"c"c, "a"c, "$"c}
Console.WriteLine(letters.LastIndexOf("c"c))
Console.WriteLine(letters.LastIndexOf("a"c, 25))
Console.WriteLine(letters.LastIndexOf("$"c, 15, 5))
End Sub
End Module
|
15
13
-1
2.28.9.Converts a substring within a string to an array of
characters, then enumerates and displays the elements of the array.
|
' Sample for String.ToCharArray(Int32, Int32)
Imports System
Class Sample
Public Shared Sub Main()
Dim str As String = "012wxyz789"
Dim arr() As Char
arr = str.ToCharArray(3, 4)
Console.Write("The letters in '{0}' are: '", str)
Console.Write(arr)
Console.WriteLine("Each letter in '{0}' is:", str)
Dim c As Char
For Each c In arr
Console.WriteLine(c)
Next c
End Sub
End Class
|
2.29.String Array
2.29.1.String array
|
Module Test
Public Sub Main()
Dim sMonths() As String = {"Jan", "Feb", "Mar", "Apr", "May", "Jun", "Jul", "Aug", "Sep", Oct", "Nov", "Dec"}
Console.WriteLine("Eleventh month of the year = {0}", sMonths(10))
End Sub
End Module
|
Eleventh month of the year = Nov
2.29.2.Use For Each Loop to output a String array
|
Public Class Tester
Public Shared Sub Main
Dim fruitArray() As String = {"Oranges", "Apples", "Grapes", "Bananas", "Blueberries"}
For Each fruit As String In fruitArray
Console.WriteLine(fruit)
Next fruit
End Sub
End Class
|
Oranges
Apples
Grapes
Bananas
Blueberries
2.29.3.Array.Reverse a string array
|
Imports System.Collections
public class Test
public Shared Sub Main
Dim StringArray() As String = {"This", "is", "a", "test"}
Array.Reverse(StringArray)
Dim E As IEnumerator = StringArray.GetEnumerator()
While (E.MoveNext())
Console.WriteLine(E.Current())
End While
End Sub
End class
|
test
a
is
This
2.29.4.Array.Sort a string array
|
Imports System.Collections
public class Test
public Shared Sub Main
Dim StringArray() As String = {"This", "is", "a", "test"}
Array.Sort(StringArray)
Dim E As IEnumerator = StringArray.GetEnumerator()
While (E.MoveNext())
Console.WriteLine(E.Current())
End While
End Sub
End class
|
a
is
test
This
2.29.5.Two dimensional string array
|
public class Test
public Shared Sub Main
Dim str_values(,,) As String = _
{ _
{ _
{"000", "001", "002"}, _
{"010", "011", "012"} _
}, _
{ _
{"100", "101", "102"}, _
{"110", "111", "112"} _
} _
}
Console.WriteLine("")
For i As Integer = 0 To 1
For j As Integer = 0 To 1
For k As Integer = 0 To 2
Console.Write(str_values(i, j, k) & " ")
Next k
Next j
Console.WriteLine("")
Next i
End Sub
End class
|
000 001 002 010 011 012
100 101 102 110 111 112
2.29.6.Store data in a multivalue array
|
Public Class Tester
Public Shared Sub Main
Dim multiValue(2)() As String
Dim counter1 As Integer
Dim counter2 As Integer
' ----- Build the multivalue array.
multiValue(0) = New String() {"alpha", "beta", "gamma"}
multiValue(1) = New String() {"A", "B", "C", "D", "E", "F", "G", "H"}
multiValue(2) = New String() {"Yes", "No"}
' ----- Format the array for display.
For counter1 = 0 To multiValue.Length - 1
For counter2 = 0 To multiValue(counter1).Length - 1
Console.WriteLine(multiValue(counter1)(counter2))
Next counter2
Console.WriteLine("")
Next counter1
End Sub
End Class
|
alpha
beta
gamma
A
B
C
D
E
F
G
H
Yes
No
2.30.String Case
2.30.1.Change string to upper case by
using UCase
|
Class Tester
Shared Sub Main()
Dim userInput As String
userInput = " asdf "
Console.WriteLine(UCase(userInput))
End Sub
End Class
|
ASDF
2.30.2.Change string to lower case and upper case
|
Public Class Tester
Public Shared Sub Main
Dim quote As String = "AbCdEfG"
Dim result As New System.Text.StringBuilder
result.AppendLine("Original: " & quote)
result.AppendLine("Upper Case: " & quote.ToUpper())
result.AppendLine("Lower Case: " & quote.ToLower())
result.AppendLine("Mixed Case: " & MixedCase(quote))
Console.WriteLine(result.ToString())
End Sub
Public Shared Function MixedCase(ByVal origText As String) As String
Dim counter As Integer
Dim textParts() As String = Split(origText, " ")
For counter = 0 To textParts.Length - 1
If (textParts(counter).Length > 0) Then _
textParts(counter) = _
UCase(Microsoft.VisualBasic.Left( _
textParts(counter), 1)) & _
LCase(Mid(textParts(counter), 2))
Next counter
Return Join(textParts, " ")
End Function
End Class
|
Original: AbCdEfG
Upper Case: ABCDEFG
Lower Case: abcdefg
Mixed Case: Abcdefg
2.30.3.Capitalize the first letter
|
Public Class Tester
Public Shared Sub Main
Dim quote As String = "AbCdEfG"
Dim result As New System.Text.StringBuilder
result.AppendLine("Original: " & quote)
result.AppendLine("Upper Case: " & quote.ToUpper())
result.AppendLine("Lower Case: " & quote.ToLower())
result.AppendLine("Mixed Case: " & MixedCase(quote))
Console.WriteLine(result.ToString())
End Sub
Public Shared Function MixedCase(ByVal origText As String) As String
Dim counter As Integer
Dim textParts() As String = Split(origText, " ")
For counter = 0 To textParts.Length - 1
If (textParts(counter).Length > 0) Then _
textParts(counter) = _
UCase(Microsoft.VisualBasic.Left( _
textParts(counter), 1)) & _
LCase(Mid(textParts(counter), 2))
Next counter
Return Join(textParts, " ")
End Function
End Class
|
Original: AbCdEfG
Upper Case: ABCDEFG
Lower Case: abcdefg
Mixed Case: Abcdefg
2.31.String Compare
2.31.1.Comparing strings: Equals, =,
String.Equals() and CompareTo
|
Module Tester
Sub Main()
Dim string1 As String = "hello"
Dim string2 As String = "good bye"
Dim string3 As String = "Happy Birthday"
Dim string4 As String = "happy birthday"
Dim output As String
Dim quotes As Char = ChrW(34)
If (string1.Equals("hello")) Then
Console.WriteLine("string1 equals hello")
Else
Console.WriteLine("not equal ")
End If
' test for equality with =
If string1 = "hello" Then
Console.WriteLine("string1 equals " & quotes & "hello" & quotes )
Else
Console.WriteLine("string1 does not equal " & quotes & "hello" & quotes)
End If
If (String.Equals(string3, string4)) Then
Console.WriteLine("string3 equals string4")
Else
Console.WriteLine("string3 does not equal string4")
End If
' test CompareTo
Console.WriteLine("string1.CompareTo(string2) is " & _
string1.CompareTo(string2) & vbCrLf & _
"string2.CompareTo(string1) is " & _
string2.CompareTo(string1) & vbCrLf & _
"string1.CompareTo(string1) is " & _
string1.CompareTo(string1) & vbCrLf & _
"string3.CompareTo(string4) is " & _
string3.CompareTo(string4) & vbCrLf & _
"string4.CompareTo(string3) is " & _
string4.CompareTo(string3))
End Sub ' Main
End Module
|
string1 equals hello
string1 equals "hello
string3 does not equal string4
string1.CompareTo(string2) is 1
string2.CompareTo(string1) is -1
string1.CompareTo(string1) is 0
string3.CompareTo(string4) is 1
string4.CompareTo(string3) is -1
2.31.2.String Equals with overloaded operator, member method and
static member method
|
Option Strict On
Imports System
Class Tester
Public Shared Sub Main( )
Dim s1 As String = "abcd"
Dim s2 As String = "ABCD"
' the String copy method
Dim s5 As String = String.Copy(s2)
Console.WriteLine("s5 copied from s2: {0}", s5)
' copy with the overloaded operator
Dim s6 As String = s5
Console.WriteLine("s6 = s5: {0}", s6)
' member method
Console.WriteLine("Does s6.Equals(s5)?: {0}", s6.Equals(s5))
' shared method
Console.WriteLine("Does Equals(s6,s5)?: {0}", _
String.Equals(s6, s5))
End Sub 'Main
End Class 'Tester
|
s5 copied from s2: ABCD
s6 = s5: ABCD
Does s6.Equals(s5)?: True
Does Equals(s6,s5)?: True
2.31.3.String Compare with case sensitive and insensitive
|
Class Tester
Shared Sub Main( )
Dim s1 As [String] = "abcd"
Dim s2 As [String] = "ABCD"
Dim result As Integer
result = [String].Compare(s1, s2)
Console.WriteLine("compare s1: {0}, s2: {1}, result: {2}" _
& Environment.NewLine, s1, s2, result)
result = [String].Compare(s1, s2, True)
Console.WriteLine("Compare insensitive. result: {0}" _
& Environment.NewLine, result)
End Sub
End Class
|
compare s1: abcd, s2: ABCD, result: -1
Compare insensitive. result: 0
2.31.4.Compare String value in If statement
|
Module Module1
Sub Main()
Dim Language As String = "English"
If (Language = "English") Then
Console.WriteLine("Hello, world!")
ElseIf (Language = "Spanish") Then
Console.WriteLine("Hola, mundo")
End If
End Sub
End Module
|
Hello, world!
2.31.5.Whether a string is the prefix or suffix of another string.
|
Imports System
Imports System.Globalization
Public Class SamplesCompareInfo
Public Shared Sub Main()
Dim myStr1 As [String] = "this"
Dim myStr2 As [String] = "is"
Dim myXfix As [String] = "th"
' Uses the CompareInfo property of the InvariantCulture.
Dim myComp As CompareInfo = CultureInfo.InvariantCulture.CompareInfo
' Determines whether myXfix is a prefix of "calle" and "llegar".
Console.WriteLine("IsPrefix( {0}, {1} ) : {2}", myStr1, myXfix, myComp.IsPrefix(myStr1, myXfix))
Console.WriteLine("IsPrefix( {0}, {1} ) : {2}", myStr2, myXfix, myComp.IsPrefix(myStr2, myXfix))
' Determines whether myXfix is a suffix of "calle" and "llegar".
Console.WriteLine("IsSuffix( {0}, {1} ) : {2}", myStr1, myXfix, myComp.IsSuffix(myStr1, myXfix))
Console.WriteLine("IsSuffix( {0}, {1} ) : {2}", myStr2, myXfix, myComp.IsSuffix(myStr2, myXfix))
End Sub
End Class
|
2.31.6.Use the CompareTo method with
another String.
|
Imports System
Public Class MainClass
Public Shared Sub Main()
Dim strFirst As String = "Goodbye"
Console.WriteLine(CompareStrings(strFirst, strFirst))
End Sub
Private Shared Function CompareStrings(str1 As String, str2 As String) As String
Dim cmpVal As Integer = str1.CompareTo(str2)
If cmpVal = 0 Then
Return "The strings have the same value!"
Else
If cmpVal > 0 Then
Return "The first string is greater than the second string!"
Else
Return "The second string is greater than the first string!"
End If
End If
End Function
End Class
|
2.31.7.Use String.Compare to check if a
URI is a file URI
|
Public Class SamplesCompareInfo
Public Shared Sub Main()
End Sub
Shared Function IsFileURI(ByVal path As String) As Boolean
If String.Compare(path, 0, "file:", 0, 5, StringComparison.OrdinalIgnoreCase) = 0 Then
Return True
Else
Return False
End If
End Function
End Class
|
2.31.8.Compare two strings using
different CompareOptions settings.
|
Imports System
Imports System.Globalization
Public Class SamplesCompareInfo
Public Shared Sub Main()
Dim myStr1 As [String] = "B"
Dim myStr2 As [String] = "b"
Dim myComp As CompareInfo = CultureInfo.InvariantCulture.CompareInfo
Console.WriteLine(" With no CompareOptions : {0}", myComp.Compare(myStr1, myStr2))
Console.WriteLine(" With None : {0}", myComp.Compare(myStr1, myStr2, CompareOptions.None))
Console.WriteLine(" With Ordinal : {0}", myComp.Compare(myStr1, myStr2, CompareOptions.Ordinal))
Console.WriteLine(" With StringSort : {0}", myComp.Compare(myStr1, myStr2, CompareOptions.StringSort))
Console.WriteLine(" With IgnoreCase : {0}", myComp.Compare(myStr1, myStr2, CompareOptions.IgnoreCase))
Console.WriteLine(" With IgnoreSymbols : {0}", myComp.Compare(myStr1, myStr2, CompareOptions.IgnoreSymbols))
Console.WriteLine(" With IgnoreCase and IgnoreSymbols : {0}", myComp.Compare(myStr1, myStr2, CompareOptions.IgnoreCase Or CompareOptions.IgnoreSymbols))
End Sub
End Class
|
2.32.String Copy
2.32.1.Use the String Copy method
|
Option Strict On
Imports System
Class Tester
Public Shared Sub Main( )
Dim s1 As String = "abcd"
Dim s2 As String = "ABCD"
' the String copy method
Dim s5 As String = String.Copy(s2)
Console.WriteLine("s5 copied from s2: {0}", s5)
End Sub 'Main
End Class 'Tester
|
s5 copied from s2: ABCD
2.32.2.Use the overloaded operator (=) to copy string
|
Option Strict On
Imports System
Class Tester
Public Shared Sub Main( )
Dim s1 As String = "abcd"
Dim s2 As String = "ABCD"
Dim s6 As String = s1
Console.WriteLine("s6 = s1: {0}", s6)
End Sub 'Main
End Class 'Tester
|
s6 = s1: abcd
2.33.String Find
2.33.1.Demonstrating StartsWith and
EndsWith methods
|
Module Tester
Sub Main()
Dim strings As String()
Dim output As String = ""
Dim i As Integer
Dim quotes As Char = ChrW(34)
strings = New String() {"started", "starting", _
"ended", "ending"}
For i = 0 To strings.GetUpperBound(0)
If strings(i).StartsWith("st") Then
Console.WriteLine(" starts with st")
End If
Next
For i = 0 To strings.GetUpperBound(0)
If strings(i).EndsWith("ed") Then
Console.WriteLine(" ends with ed" )
End If
Next
End Sub ' Main
End Module
|
starts with st
starts with st
ends with ed
ends with ed
2.33.2.Return the index of the string
|
Option Strict On
Imports System
Class Tester
Public Shared Sub Main( )
Dim s1 As String = "abcd"
Dim s2 As String = "ABCD"
Dim s3 As String = "AAAAs "
s3 = s3 & "development"
Console.WriteLine("s3: {0}", s3)
Console.Write("The first occurrence of a ")
Console.WriteLine(s3.IndexOf("a"))
End Sub 'Main
End Class 'Tester
|
s3: AAAAs development
The first occurrence of a -1
2.33.3.Use IndexOf to locate a substring in a string
|
Module Tester
Sub Main()
Dim letters As String = "abcdefghijklmabcdefghijklm"
Dim searchLetters As Char() = New Char() {"c"c, "a"c, "$"c}
Console.WriteLine(letters.IndexOf("def"))
Console.WriteLine(letters.IndexOf("def", 7))
Console.WriteLine(letters.IndexOf("hello", 5, 15))
End Sub
End Module
|
3
16
-1
2.33.4.Use LastIndexOf to find a substring in a string
|
Module Tester
Sub Main()
Dim letters As String = "abcdefghijklmabcdefghijklm"
Dim searchLetters As Char() = New Char() {"c"c, "a"c, "$"c}
Console.WriteLine(letters.LastIndexOf("def"))
Console.WriteLine(letters.LastIndexOf("def", 25))
Console.WriteLine(letters.LastIndexOf("hello", 20, 15))
End Sub
End Module
|
16
16
-1
2.33.5.Use IndexOfAny to find first occurrence of character in array
|
Module Tester
Sub Main()
Dim letters As String = "abcdefghijklmabcdefghijklm"
Dim searchLetters As Char() = New Char() {"c"c, "a"c, "$"c}
Console.WriteLine("First occurrence of ""c""," & _
" ""a"" or ""$"" is located at " & _
letters.IndexOfAny(searchLetters))
Console.WriteLine("First occurrence of ""c"", ""a"" or " & _
"""$"" is located at " & _
letters.IndexOfAny(searchLetters, 7))
Console.WriteLine("First occurrence of ""c"", ""a"" or " & _
"""$"" is located at " & _
letters.IndexOfAny(searchLetters, 20, 5))
End Sub
End Module
|
First occurrence of "c", "a" or "$" is located at 0
First occurrence of "c", "a" or "$" is located at 13
First occurrence of "c", "a" or "$" is located at -1
2.33.6.Use LastIndexOfAny to find first occurrence of character in
array
|
Module Tester
Sub Main()
Dim letters As String = "abcdefghijklmabcdefghijklm"
Dim searchLetters As Char() = New Char() {"c"c, "a"c, "$"c}
Console.WriteLine("Last occurrence of ""c""," & _
" ""a"" or ""$"" is located at " & _
letters.LastIndexOfAny(searchLetters))
Console.WriteLine("Last occurrence of ""c"", ""a"" or " & _
"""$"" is located at " & _
letters.LastIndexOfAny(searchLetters, 1))
Console.WriteLine("Last occurrence of ""c"", ""a"" or " & _
"""$"" is located at " & _
letters.LastIndexOfAny(searchLetters, 25, 5))
End Sub
End Module
|
Last occurrence of "c", "a" or "$" is located at 15
Last occurrence of "c", "a" or "$" is located at 0
Last occurrence of "c", "a" or "$" is located at -1
2.33.7.String Index of any
|
public class Test
public Shared Sub Main
Dim s1 As New String("Greeting")
Console.WriteLine(s1.IndexOfAny("tin"))
End Sub
End class
|
4
2.33.8.Use the LastIndexOf(Char) method to find the last directory
separator character in a string
|
Imports System.IO
Public Module Test
Public Sub Main()
Dim filename As String
filename = ExtractFilename("C:\delegate.txt")
Console.WriteLine(filename)
End Sub
Public Function ExtractFilename(filepath As String) As String
If filepath.Trim().EndsWith("\") Then Return String.Empty
Dim position As Integer = filepath.LastIndexOf("\"c)
If position = -1 Then
If File.Exists(Environment.CurrentDirectory + Path.DirectorySeparatorChar + filepath) Then
Return filepath
Else
Return String.Empty
End If
Else
If File.Exists(filepath) Then
Return filepath.Substring(position + 1)
Else
Return String.Empty
End If
End If
End Function
End Module
|
2.33.9.EndsWith method.
|
Imports System
Public Class EndsWithTest
Public Shared Sub Main()
Dim strSource As String() = { "<b>This is bold text</b>","wrong>"}
Dim s As String
For Each s In strSource
Console.WriteLine(StripEndTags(s))
Next s
End Sub
Private Shared Function StripEndTags(item As String) As String
If item.Trim().EndsWith(">") Then
Dim lastLocation As Integer = item.LastIndexOf("</")
If lastLocation >= 0 Then
item = item.Substring(0, lastLocation)
End If
End If
Return Item
End Function
End Class
|
2.33.10.Find the index of the last
occurrence of any character in the string "is" within
another string.
|
Imports System
Class Sample
Public Shared Sub Main()
Dim str As String = "this is a test."
Dim start As Integer
Dim at As Integer
Dim target As String = "is"
Dim anyOf As Char() = target.ToCharArray()
at = str.LastIndexOfAny(anyOf)
If at > - 1 Then
Console.Write(at)
Else
Console.Write("(not found)")
End If
End Sub
End Class
|
2.33.11.IsMatch(String) determines
whether a string is a valid to Regular expression
|
Imports System.Text.RegularExpressions
Module Example
Public Sub Main()
Dim rgx As New Regex("^[a-zA-Z0-9]\d{2}[a-zA-Z0-9](-\d{3}){2}[A-Za-z0-9]$")
Console.WriteLine(rgx.IsMatch("1298-673-4192"))
End Sub
End Module
|
2.34.String Format
2.34.1.String.Format: {0,10:p}
|
Public Class Tester
Public Shared Sub Main
Console.WriteLine(String.Format("{0,10:p}", 0.32))
End Sub
End Class
|
32.00 %
2.34.2.String.Format: {0:#,### ; #.## ,00##,00}
|
Public Class Tester
Public Shared Sub Main
Console.WriteLine(String.Format("{0:#,### ; #.## ,00##,00}",1232.2345))
End Sub
End Class
|
0.0
2.34.3.String.Format: {0:##.## ; -##.# ; 0.0#} (2)
|
Public Class Tester
Public Shared Sub Main
Console.WriteLine(String.Format("{0:##.## ; -##.# ; 0.0#}", -1235.33))
End Sub
End Class
|
-1235.3
2.34.4.String.Format: {0:##.## ; (##.00) ; 0.0#} (3)
|
Public Class Tester
Public Shared Sub Main
Console.WriteLine(String.Format("{0:##.## ; (##.00) ; 0.0#}", 0))
End Sub
End Class
|
0.0
2.34.5.String format: {0, 1:D}
|
Module Module1
Sub Main()
Dim A As Double = 1.23456789
Console.WriteLine("{0, 1:D} {1, 2:D} {2, 3:D}", 1, 2, 3)
End Sub
End Module
|
1 2 3
2.34.6.String format: {0, 7:F1}
|
Module Module1
Sub Main()
Dim A As Double = 1.23456789
Console.WriteLine("{0, 7:F1} {1, 7:F3} {2, 7:F5}", A, A, A)
End Sub
End Module
|
1.2 1.235 1.23457
2.34.7.String format: {0, 0:#.#}, {0, 0:#.###}, {0, 0:#.#####} (4)
|
Module Module1
Sub Main()
Dim A As Double = 1.23456789
Console.WriteLine("{0, 0:#.#}", A)
Console.WriteLine("{0, 0:#.###}", A)
Console.WriteLine("{0, 0:#.#####}", A)
End Sub
End Module
|
1.2
1.235
1.23457
2.35.String Pad
2.35.1.String.Pad
|
public class Test
public Shared Sub Main
Dim strLeftPad, strRightPad As String
strLeftPad = "[" & "Visual Basic Express".PadLeft(28) & "]"
strRightPad = "[" & "Visual Basic Express".PadRight(28) & "]"
Console.WriteLine(strLeftPad & vbCrLf & strRightPad)
strLeftPad = "[" & "Visual Basic Express".PadLeft(28, "@") & "]"
strRightPad = "[" & "Visual Basic Express".PadRight(28, ".") & "]"
Console.WriteLine(strLeftPad & vbCrLf & strRightPad)
End Sub
End class
|
[ Visual Basic Express]
[Visual Basic Express ]
[@@@@@@@@Visual Basic Express]
[Visual Basic Express........]
2.35.2.PadLeft, PadRight and PadCenter
|
Public Class Tester
Public Shared Sub Main
Dim content1 As String
Dim content2 As String
Dim content3 As String
Dim content4 As String
content1 = "Not padded"
content2 = "PadLeft".PadLeft(50)
content3 = "PadRight".PadRight(50)
content4 = "PadCenter"
content4 = content4.PadLeft((50 + _
content4.Length) \ 2).PadRight(50)
Console.WriteLine(String.Format("{0}{4}{1}{4}{2}{4}{3}", _
content1, content2, content3, content4, vbNewLine))
End Sub
End Class
|
Not padded
PadLeft
PadRight
PadCenter
2.35.3.PadLeft, PadRight and PadCenter with dot
|
Public Class Tester
Public Shared Sub Main
Dim content1 As String
Dim content2 As String
Dim content3 As String
Dim content4 As String
content1 = "Not padded"
content2 = "PadLeft".PadLeft(50, "."c)
content3 = "PadRight".PadRight(50, "."c)
content4 = "PadCenter"
content4 = content4.PadLeft((50 + content4.Length) \ 2, _
"."c).PadRight(50, "."c)
Console.WriteLine(String.Format("{0}{4}{1}{4}{2}{4}{3}", _
content1, content2, content3, content4, vbNewLine))
End Sub
End Class
|
Not padded
...........................................PadLeft
PadRight..........................................
....................PadCenter.....................
2.36.String Replace
2.36.1.Replace a sub string with
'Replace'
|
Class Tester
Shared Sub Main()
Dim userInput As String
userInput = " asdf "
Console.WriteLine(Replace(userInput, "f", ""))
End Sub
End Class
|
asd
2.36.2.Replace substring with another substring
|
public class Test
public Shared Sub Main
Dim s1 As New String("Greeting")
s1 = s1.Replace("e", "i")
Console.WriteLine(s1)
End Sub
End class
|
Griiting
2.37.String Split
2.37.1.String split by using the Split,
String.Split()
|
Public Class Tester
Public Shared Sub Main
Dim quote As String = "The important thing is not to " & _
"stop questioning. --Albert Einstein"
Dim strArray1() As String = Split(quote, "ing")
Dim strArray2() As String = quote.Split(CChar("ing"))
Dim counter As Integer
For counter = 0 To strArray1.Length - 1
Console.WriteLine(strArray1(counter))
Next counter
For counter = 0 To strArray2.Length - 1
Console.WriteLine(strArray2(counter))
Next counter
End Sub
End Class
|
The important th
is not to stop question
. --Albert Einstein
The
mportant th
ng
s not to stop quest
on
ng. --Albert E
nste
n
2.37.2.Use Regular Expression to Split string
|
Imports System
Imports System.Text
Imports System.Text.RegularExpressions
Class Tester
Public Shared Sub Main( )
Dim s1 As String = "One,Two,Three Four"
Dim theRegex As New Regex(" |, |,")
Dim sBuilder As New StringBuilder( )
Dim id As Integer = 1
Dim subString As String
For Each subString In theRegex.Split(s1)
id = id + 1
sBuilder.AppendFormat("{0}: {1}" & Environment.NewLine, id, subString)
Next subString
Console.WriteLine("{0}", sBuilder)
End Sub
End Class
|
2: One
3: Two
4: Three
5: Four
2.37.3.String Split
|
Option Strict On
Imports System
Class Tester
Public Shared Sub Main( )
Dim s1 As String = "One,Two,Three Liberty Associates, Inc."
Const Space As Char = " "c
Const Comma As Char = ","c
Dim delimiters( ) As Char = {Space, Comma}
Dim output As String = ""
Dim ctr As Integer = 0
Dim resultArray As String( ) = s1.Split(delimiters)
Dim subString As String
For Each subString In resultArray
ctr = ctr + 1
output &= ctr.ToString( )
output &= ": "
output &= subString
output &= Environment.NewLine
Next subString
Console.WriteLine(output)
End Sub 'Main
End Class 'Tester
|
1: One
2: Two
3: Three
4: Liberty
5: Associates
6:
7: Inc.
2.37.4.Use the StringSplitOptions enumeration to include or exclude
substrings generated by the Split method.
|
Imports System
Class Sample
Public Shared Sub Main()
Dim s1 As String = ",ONE,,TWO,,,THREE,,"
Dim s2 As String = "[stop]" & _
"ONE[stop][stop]" & _
"TWO[stop][stop][stop]" & _
"THREE[stop][stop]"
Dim charSeparators() As Char = {","c}
Dim stringSeparators() As String = {"[stop]"}
Dim result() As String
result = s1.Split(charSeparators, StringSplitOptions.None)
Show(result)
result = s1.Split(charSeparators, StringSplitOptions.RemoveEmptyEntries)
Show(result)
result = s1.Split(charSeparators, 2, StringSplitOptions.None)
Show(result)
result = s1.Split(charSeparators, 2, StringSplitOptions.RemoveEmptyEntries)
Show(result)
result = s2.Split(stringSeparators, StringSplitOptions.None)
Show(result)
result = s2.Split(stringSeparators, StringSplitOptions.RemoveEmptyEntries)
Show(result)
result = s2.Split(stringSeparators, 2, StringSplitOptions.None)
Show(result)
result = s2.Split(stringSeparators, 2, StringSplitOptions.RemoveEmptyEntries)
Show(result)
End Sub
Public Shared Sub Show(ByVal entries() As String)
Console.WriteLine("The return value contains these {0} elements:", entries.Length)
Dim entry As String
For Each entry In entries
Console.Write("<{0}>", entry)
Next entry
Console.Write(vbCrLf & vbCrLf)
End Sub
End Class
|
2.38.String Functions
2.38.1.Passing String values to Val
|
Option Strict On
Public Module Tester
Public Sub Main()
'
Console.WriteLine(Val("913.3"))
Console.WriteLine(Val("131AC57"))
Console.WriteLine(Val("-132.23"))
Console.WriteLine(Val("+1203.22"))
Console.WriteLine(Val("A0545"))
Console.WriteLine()
End Sub
End Module
|
913.3
131
-132.23
1203.22
0
2.38.2.Passing formatted numeric values to Val
|
Option Strict On
Public Module Tester
Public Sub Main()
' Passing formatted numeric values to Val
Console.WriteLine(Val("$1034.51"))
Console.WriteLine(Val("1,032.54"))
End Sub
End Module
|
0
1
2.38.3.IsNumeric, IsDate, IsNothing
|
Public Class Tester
Public Shared Sub Main
Dim theData As String = Nothing
Dim result As New System.Text.StringBuilder
' ----- Format nothing.
result.AppendLine(String.Format( _
"IsNumeric({0}) ... {1}", theData, IsNumeric(theData)))
result.AppendLine(String.Format( _
"IsDate({0}) ... {1}", theData, IsDate(theData)))
result.AppendLine(String.Format( _
"IsNothing({0}) ... {1}", theData, IsNothing(theData)))
result.AppendLine()
' ----- Format a number in a string.
theData = "-12.345"
result.AppendLine(String.Format( _
"IsNumeric({0}) ... {1}", theData, IsNumeric(theData)))
result.AppendLine(String.Format( _
"IsDate({0}) ... {1}", theData, IsDate(theData)))
result.AppendLine(String.Format( _
"IsNothing({0}) ... {1}", theData, IsNothing(theData)))
result.AppendLine()
' ----- Format a date in a string.
theData = "July 17, 2007"
result.AppendLine(String.Format( _
"IsNumeric({0}) ... {1}", theData, IsNumeric(theData)))
result.AppendLine(String.Format( _
"IsDate({0}) ... {1}", theData, IsDate(theData)))
result.Append(String.Format( _
"IsNothing({0}) ... {1}", theData, IsNothing(theData)))
Console.WriteLine(result.ToString())
End Sub
End Class
|
IsNumeric() ... False
IsDate() ... False
IsNothing() ... True
IsNumeric(-12.345) ... True
IsDate(-12.345) ... False
IsNothing(-12.345) ... False
IsNumeric(July 17, 2007) ... False
IsDate(July 17, 2007) ... True
IsNothing(July 17, 2007) ... False
2.38.4.Duplicate a string
|
Public Class Tester
Public Shared Sub Main
Console.WriteLine(StrDup(30, "-"))
End Sub
End Class
|
------------------------------
2.38.5.Get string index by using InStr
|
Class Tester
Shared Sub Main()
Dim userInput As String
userInput = " asdf "
Console.WriteLine(InStr(userInput, "f"))
End Sub
End Class
|
6
2.38.6.CStr: Convert Double to String
|
Public Class Tester
Public Shared Sub Main
Dim x As Double
x = 12345678901234567890D
Console.WriteLine(CStr(x))
End Sub
End Class
|
1.23456789012346E+19
2.38.7.Len: get string length
|
Public Class Tester
Public Shared Sub Main
Console.WriteLine(Len("txtString1.Text"))
End Sub
End Class
|
15
2.38.8.Instr
|
Public Class Tester
Public Shared Sub Main
Dim MyString As String, YourString As String
MyString = "asdf"
YourString = "fdsa"
Console.WriteLine(InStr(2, MyString, YourString))
End Sub
End Class
|
0
2.38.9.IsDBNull
|
Public Module modMain
Public Sub Main()
Dim title As String = "Mr."
Dim name As Object = DBNull.Value
Dim addressLine1 As String = title & " " & name
If IsDBNull(addressLine1) Then
Console.WriteLine("Null value")
Else
Console.WriteLine(addressLine1)
End If
End Sub
End Module
|
Mr.
2.38.10.Microsoft.VisualBasic.Left
|
public class Test
public Shared Sub Main
Dim strName As String = "Visual Basic Express"
If Microsoft.VisualBasic.Left(strName, 3) = "Vis" Then Console.WriteLine("True")
If strName.StartsWith("Vis") Then Console.WriteLine("True")
End Sub
End class
|
True
True
2.38.11.String.Copy
|
public class Test
public Shared Sub Main
Dim str1, str2 As String
str1 = "some text"
str2 = str1
str2 = String.Copy(str1)
Console.WriteLine(str1 & vbCrLf & str2)
End Sub
End class
|
some text
some text
2.38.12.Use String.Concat to concatenate two strings
|
public class Test
public Shared Sub Main
Dim aryStrings() As String = {"string1", "string2", "string3", "string4"}
Dim strLongString As String
strLongString = String.Concat(aryStrings)
Console.WriteLine(strLongString)
End Sub
End class
|
string1string2string3string4
2.38.13.Format: c
|
Public Class Tester
Public Shared Sub Main
Console.WriteLine( Format(123, "c") )
End Sub
End Class
|
2.38.14.String handling function: Len
|
Module Tester
Public Sub Main()
Dim sHello As String = "Hello World"
Console.WriteLine("Original string: {0}", sHello)
Console.WriteLine("Length of string (Len(sHello)): {0}", Len(sHello))
End Sub
End Module
|
Original string: Hello World
Length of string (Len(sHello)): 11
2.38.15.Left: get characters from left
|
Module Tester
Public Sub Main()
Dim sHello As String = "Hello World"
Console.WriteLine("Original string: {0}", sHello)
Console.WriteLine("Leftmost two characters (Left(sHello, 2)): {0}", Left(sHello, 2))
End Sub
End Module
|
Original string: Hello World
Leftmost two characters (Left(sHello, 2)): He
|
2.38.16.Right: get characters from right
|
|
Module Tester
Public Sub Main()
Dim sHello As String = "Hello World"
Console.WriteLine("Original string: {0}", sHello)
Console.WriteLine("Rightmost four characters (Right(sHello, 4)): {0}", Right(sHello, 4))
End Sub
End Module
|
|
|
Original string: Hello World
Rightmost four characters (Right(sHello, 4)): orld
|
2.38.17.Mid(string, 4, 5): get sub
string from middle
|
Module Tester
Public Sub Main()
Dim sHello As String = "Hello World"
Console.WriteLine("Original string: {0}", sHello)
Console.WriteLine("From middle of string (Mid(sHello, 4, 5)): {0}", Mid(sHello, 4, 5))
End Sub
End Module
|
Original string: Hello World
From middle of string (Mid(sHello, 4, 5)): lo Wo
2.38.18.Mid(string, 7): get sub string from start
|
Module Tester
Public Sub Main()
Dim sHello As String = "Hello World"
Console.WriteLine("Original string: {0}", sHello)
Console.WriteLine("Starting with character (Mid(sHello, 7)): {0}", Mid(sHello, 7))
End Sub
End Module
|
Original string: Hello World
Starting with character (Mid(sHello, 7)): World
2.38.19.Instr: find character in a string
|
Module Tester
Public Sub Main()
Dim sHello As String = "Hello World"
Console.WriteLine("Original string: {0}", sHello)
Console.WriteLine("Find character (Instr(1, sHello, 'l')) : {0}", InStr(1, sHello, "l"))
End Sub
End Module
|
Original string: Hello World
Find character (Instr(1, sHello, 'l')) : 3
2.38.20.Instr: find sub string a in a string
|
Module Tester
Public Sub Main()
Dim sHello As String = "Hello World"
Console.WriteLine("Original string: {0}", sHello)
Console.WriteLine("Find substring (Instr(1, sHello, 'World')) : {0}", InStr(1, sHello, "Wor
ld"))
End Sub
End Module
|
Original string: Hello World
Find substring (Instr(1, sHello, 'World')) : 7
2.38.21.LCase: change string to lower case
|
Module Tester
Public Sub Main()
Dim sHello As String = "Hello World"
Console.WriteLine("Original string: {0}", sHello)
Console.WriteLine("Lowercase (LCase(sHello)) : {0}", LCase(sHello))
End Sub
End Module
|
Original string: Hello World
Lowercase (LCase(sHello)) : hello world
2.38.22.UCase: change string to upper case
|
Module Tester
Public Sub Main()
Dim sHello As String = "Hello World"
Console.WriteLine("Original string: {0}", sHello)
Console.WriteLine("Uppercase (UCase(sHello)) : {0}", UCase(sHello))
End Sub
End Module
|
Original string: Hello World
Uppercase (UCase(sHello)) : HELLO WORLD
2.38.23.Change string case using the English-United States and
Turkish-Turkey cultures and then compare
|
' Sample for String.ToUpper(CultureInfo)
Imports System
Imports System.Globalization
Imports Microsoft.VisualBasic
Class Sample
Public Shared Sub Main()
Dim str1 As [String] = "idea"
Dim str2, str3 As [String]
Console.WriteLine("str2 = Upper case copy of str1 using English-United States culture.")
str2 = str1.ToUpper(New CultureInfo("en-US", False))
Console.WriteLine("str3 = Upper case copy of str1 using Turkish-Turkey culture.")
str3 = str1.ToUpper(New CultureInfo("tr-TR", False))
Console.WriteLine("str2 is {0} to str3.", IIf(0 = [String].CompareOrdinal(str2, str3), "equal", "not equal"))
DeCode(str1)
DeCode(str2)
DeCode(str3)
End Sub
Public Shared Sub DeCode( s As [String])
Dim c As Char
For Each c In s
Console.Write("{0:x4} ", AscW(c))
Next c
Console.WriteLine()
End Sub
End Class
|
2.38.24.Determines whether a string is
normalized to various normalization forms(String.Normalize and the
String.IsNormalized method)
|
Imports System
Imports System.Text
Imports Microsoft.VisualBasic
Class Sample
Public Shared Sub Main()
Dim s1 = New [String](New Char() {ChrW(&H0063), ChrW(&H0301), ChrW(&H0327), ChrW(&H00BE)})
Dim s2 As String = Nothing
Try
Show("s1", s1)
Console.WriteLine("A1) Is s1 normalized to the default form (Form C)?: {0}", s1.IsNormalized())
Console.WriteLine("A2) Is s1 normalized to Form C?: {0}", s1.IsNormalized(NormalizationForm.FormC))
Console.WriteLine("A3) Is s1 normalized to Form D?: {0}", s1.IsNormalized(NormalizationForm.FormD))
Console.WriteLine("A4) Is s1 normalized to Form KC?: {0}", s1.IsNormalized(NormalizationForm.FormKC))
Console.WriteLine("A5) Is s1 normalized to Form KD?: {0}", s1.IsNormalized(NormalizationForm.FormKD))
Catch e As Exception
Console.WriteLine(e.Message)
End Try
End Sub
Private Shared Sub Show(title As String, s As String)
Console.Write("Characters in string {0} = ", title)
Dim x As Char
For Each x In s.ToCharArray()
Console.Write("{0:X4} ", AscW(x))
Next x
Console.WriteLine()
End Sub
End Class
|
2.39.Convert from String
2.39.1.Is a string a numeric value
|
Class Tester
Shared Sub Main()
Dim userInput As String
userInput = " asdf "
Console.WriteLine(IsNumeric(userInput) = False)
End Sub
End Class
|
True
2.39.2.Convert string to value
|
Class Tester
Shared Sub Main()
Dim userInput As String
userInput = "4"
Console.WriteLine(Val(userInput))
End Sub
End Class
|
4
2.39.3.Interpret numeric strings as a hexadecimal value and convert
it to an unsigned long integer.
|
Module Example
Public Sub Main()
Dim hexStrings() As String = { "8", "0FFFFFFF", "F00", "00A", "D"}
For Each hexString As String In hexStrings
Try
Dim number As UInteger = Convert.ToUInt32(hexString, 16)
Console.WriteLine("{0,18:N0}", number)
Catch e As FormatException
Console.WriteLine("{0,18}", "Bad Format")
Catch e As OverflowException
Console.WriteLine("{0,18}", "Numeric Overflow")
Catch e As ArgumentException
Console.WriteLine("{0,18}", "Invalid in Base 16")
End Try
Next
End Sub
End Module
|
2.40.StringBuilder
2.40.1.Demonstrating StringBuilder
class constructors
|
Imports System.Text
Module Tester
Sub Main()
Dim buffer1, buffer2, buffer3 As StringBuilder
buffer1 = New StringBuilder()
buffer2 = New StringBuilder(10)
buffer3 = New StringBuilder("hello")
Console.WriteLine(buffer1.ToString())
Console.WriteLine(buffer2.ToString())
Console.WriteLine(buffer3.ToString())
End Sub ' Main
End Module
|
hello
2.40.2.StringBuilder: Insert string, Append and Replace
|
Public Class Tester
Public Shared Sub Main
Dim result As New System.Text.StringBuilder("AA ")
result.Append("CCC. ")
result.Append("AAA").Append("rrr ").Append("eee")
result.Insert(3, "note to stop ")
result.Replace("CC", "rr")
result.Insert(0, vbNewLine)
Console.WriteLine(result.ToString())
End Sub
End Class
|
AA note to stop rrC. AAArrr eee
2.40.3.Append Char to StringBuilder
|
Option Strict On
Imports System.Text
Public Module modMain
Public Sub Main()
Dim chars() As Char = {"T"c,"h"c,"i"c,"s"c," "c,"i"c,"s"c, _
" "c,"a"c,"n"c," "c,"a"c,"r"c,"r"c,"a"c, _
"y"c," "c,"o"c,"f"c," "c,"C"c,"h"c, _
"a"c,"r"c,"s"c}
Dim convertedChars As New StringBuilder
For Each ch As Char in chars
convertedChars.Append(ch)
Next
Dim displayString As String = convertedChars.ToString()
Console.WriteLine(displayString)
End Sub
End Module
|
This is an array of Chars
2.40.4.Demonstrating StringBuilder Append methods
|
Imports System.Text
Imports System.Windows.Forms
Module modBuilderAppend
Sub Main()
Dim objectValue As Object = "hello"
Dim stringValue As String = "good bye"
Dim characterArray As Char() = {"a"c, "b"c, "c"c, "d"c, "e"c, "f"c}
Dim booleanValue As Boolean = True
Dim characterValue As Char = "Z"c
Dim integerValue As Integer = 7
Dim longValue As Long = 1000000
Dim singleValue As Single = 2.5
Dim doubleValue As Double = 33.333
Dim buffer As StringBuilder = New StringBuilder()
buffer.Append(objectValue)
buffer.Append(" ")
buffer.Append(stringValue)
buffer.Append(" ")
buffer.Append(characterArray)
buffer.Append(" ")
buffer.Append(characterArray, 0, 3)
buffer.Append(" ")
buffer.Append(booleanValue)
buffer.Append(" ")
buffer.Append(characterValue)
buffer.Append(" ")
buffer.Append(integerValue)
buffer.Append(" ")
buffer.Append(longValue)
buffer.Append(" ")
buffer.Append(singleValue)
buffer.Append(" ")
buffer.Append(doubleValue)
Console.WriteLine("buffer = " & buffer.ToString())
End Sub
End Module
|
buffer = hello good bye abcdef abc True Z 7 1000000 2.5 33.333
2.40.5.StringBuilder AppendFormat
|
Imports System.Text
Class Tester
Public Shared Sub Main( )
Dim s1 As String = "One,Two,Three Liberty Associates, Inc."
Const Space As Char = " "c
Const Comma As Char = ","c
Dim delimiters( ) As Char = {Space, Comma}
Dim output As New StringBuilder( )
Dim ctr As Integer = 0
Dim resultArray As String( ) = s1.Split(delimiters)
Dim subString As String
For Each subString In resultArray
ctr = ctr + 1
output.AppendFormat("{0} : {1}" & Environment.NewLine, ctr, subString)
Next subString
Console.WriteLine(output)
End Sub
End Class
|
Your balance as of May 16, 2002 is $ 19,950.40
2.40.6.StringBuilder.AppendFormat: {0:D} is ${1: #,###.00}
|
Imports System
public class Test
public Shared Sub Main
Dim objSB As New Text.StringBuilder
objSB.AppendFormat("Your balance as of {0:D} is ${1: #,###.00}", _
#5/16/2002#, 19950.4)
Console.WriteLine(objSB.ToString)
End Sub
End class
|
Your balance as of May 16, 2002 is $ 19,950.40
2.40.7.Replace method.
|
Imports System
Imports System.Text
Class Sample
Public Shared Sub Main()
Dim str As String = "The quick br!wn d#g jumps #ver the lazy cat."
Dim sb As New StringBuilder(str)
Console.WriteLine("{0}", sb.ToString())
sb.Replace("#"c, "!"c, 15, 29) ' Some '#' -> '!'
Console.WriteLine("{0}", sb.ToString())
sb.Replace("!"c, "o"c) ' All '!' -> 'o'
Console.WriteLine("{0}", sb.ToString())
sb.Replace("cat", "dog") ' All "cat" -> "dog"
Console.WriteLine("{0}", sb.ToString())
sb.Replace("dog", "fox", 15, 20) ' Some "dog" -> "fox"
Console.WriteLine("Final value:")
Console.WriteLine("{0}", sb.ToString())
End Sub 'Main
End Class
|
2.40.8.Insert method of StringBuilder
|
Imports System
Imports System.Text
Class Sample
Private Shared sb As StringBuilder
Public Shared Sub Main()
Dim xyz As String = "xyz"
Dim abc As Char() = {"a"c, "b"c, "c"c}
Dim star As Char = "*"c
Dim obj As [Object] = 0
Dim xBool As Boolean = True
Dim xByte As Byte = 1
Dim xInt16 As Short = 2
Dim xInt32 As Integer = 3
Dim xInt64 As Long = 4
Dim xDecimal As [Decimal] = 5
Dim xSingle As Single = 6.6F
Dim xDouble As Double = 7.7
Dim xUInt16 As System.UInt16 = 8
Dim xUInt32 As System.UInt32 = 9
Dim xUInt64 As System.UInt64 = 10
Dim xSByte As System.SByte = - 11
sb = New StringBuilder()
sb.Insert(3, xyz, 2)
sb.Insert(3, xyz)
sb.Insert(3, star)
sb.Insert(3, abc)
sb.Insert(3, abc, 1, 2)
sb.Insert(3, xBool)
sb.Insert(3, obj)
sb.Insert(3, xByte)
sb.Insert(3, xInt16)
sb.Insert(3, xInt32)
sb.Insert(3, xInt64)
sb.Insert(3, xDecimal)
sb.Insert(3, xSingle)
sb.Insert(3, xDouble)
sb.Insert(3, xUInt16)
sb.Insert(3, xUInt32)
sb.Insert(3, xUInt64)
sb.Insert(3, xSByte)
Console.WriteLine(sb.ToString())
End Sub
End Class
|
2.40.9.StringBuilder: Length, Capacity,
EnsureCapacity
|
Imports System.Text
Module Tester
Sub Main()
Dim i As Integer
Dim buffer As StringBuilder = New StringBuilder("Hello, how are you?")
' use Length and Capacity properties
Console.WriteLine("buffer = " & buffer.ToString & _
vbCrLf & "Length = " & buffer.Length & vbCrLf & _
"Capacity = " & buffer.Capacity)
buffer.EnsureCapacity(75)
Console.WriteLine("New capacity = " & buffer.Capacity)
' truncate StringBuilder by setting Length property
buffer.Length = 10
Console.WriteLine("New Length = " & buffer.Length )
End Sub
End Module
|
buffer = Hello, how are you?
Length = 19
Capacity = 32
New capacity = 75
New Length = 10
2.40.10.Use StringBuilder Indexer
|
Imports System.Text
Module Tester
Sub Main()
Dim i As Integer
Dim buffer As StringBuilder = New StringBuilder("Hello, how are you?")
' use StringBuilder Indexer
For i = 0 To buffer.Length - 1
Console.WriteLine(buffer(i))
Next
End Sub
End Module
|
H
e
l
l
o
,
h
o
w
a
r
e
y
o
u
?
2.40.11.Demonstrating methods Insert and Remove of the StringBuilder
class
|
Imports System.Text
Imports System.Windows.Forms
Module Tester
Sub Main()
Dim objectValue As Object = "hello"
Dim stringValue As String = "good bye"
Dim characterArray As Char() = {"a"c, "b"c, "c"c, "d"c, "e"c, "f"c}
Dim booleanValue As Boolean = True
Dim characterValue As Char = "K"c
Dim integerValue As Integer = 7
Dim longValue As Long = 12345677890
Dim singleValue As Single = 2.5
Dim doubleValue As Double = 33.333
Dim buffer As StringBuilder = New StringBuilder()
Dim output As String
' insert values into buffer
buffer.Insert(0, objectValue)
buffer.Insert(0, " ")
buffer.Insert(0, stringValue)
buffer.Insert(0, " ")
buffer.Insert(0, characterArray)
buffer.Insert(0, " ")
buffer.Insert(0, booleanValue)
buffer.Insert(0, " ")
buffer.Insert(0, characterValue)
buffer.Insert(0, " ")
buffer.Insert(0, integerValue)
buffer.Insert(0, " ")
buffer.Insert(0, longValue)
buffer.Insert(0, " ")
buffer.Insert(0, singleValue)
buffer.Insert(0, " ")
buffer.Insert(0, doubleValue)
buffer.Insert(0, " ")
output = "buffer after inserts:" & vbCrLf & _
buffer.ToString() & vbCrLf & vbCrLf
buffer.Remove(12, 1) ' delete 5 in 2.5
buffer.Remove(2, 4) ' delete 33.3 in 33.333
output &= "buffer after Removes:" & vbCrLf & _
buffer.ToString()
Console.WriteLine(output)
End Sub ' Main
End Module
|
buffer after inserts:
33.333 2.5 12345677890 7 K True abcdef good bye hello
buffer after Removes:
33 2. 12345677890 7 K True abcdef good bye hello
2.40.12.Demonstrating method Replace
|
Imports System.Text
Imports System.Windows.Forms
Module Tester
Sub Main()
Dim builder1 As StringBuilder = New StringBuilder("Happy Birthday")
Dim builder2 As StringBuilder = New StringBuilder("good bye ")
builder1.Replace("H", "G")
builder2.Replace("g"c, "G"c, 0, 5)
Console.WriteLine(builder1.ToString() & vbCrLf & _
builder2.ToString())
End Sub ' Main
End Module
|
Gappy Birthday
Good bye
2.40.13.Use StringBuilder to reverse a string
|
Imports System
public class Test
public Shared Sub Main
Dim data As String = "abcdefgh"
Dim objSB As New Text.StringBuilder
Dim intLength As Integer = Len(data)
Dim intChar As Integer
Dim chr As Char
Dim objTS As TimeSpan
Dim dteStart As Date
objSB.Capacity = intLength
objSB.Append(data)
dteStart = Now()
For intChar = 0 To CInt(objSB.Length / 2 - 1)
chr = objSB.Chars(intChar)
objSB.Chars(intChar) = objSB.Chars(intLength - intChar - 1)
objSB.Chars(intLength - intChar - 1) = chr
Next
objTS = Now().Subtract(dteStart)
Console.WriteLine(objTS.ToString)
Console.WriteLine(objSB.ToString)
End Sub
End class
|
00:00:00
hgfedcba
2.40.14.StringBuilder.ToStrings
|
Imports System
public class Test
public Shared Sub Main
Dim objSB As New Text.StringBuilder("some text")
Console.WriteLine(objSB.ToString)
End Sub
End class
|
some text
2.40.15.Performance difference between String and StringBuilder
|
Imports System.Text
public class Test
public Shared Sub Main
Const ADD_STRING As String = "1234567890"
Dim num_trials As Long = 1000
Dim start_time As DateTime
Dim stop_time As DateTime
Dim elapsed_time As TimeSpan
Dim txt As String
Dim string_builder As New StringBuilder
txt = ""
start_time = Now
For i As Long = 1 To num_trials
txt = txt & ADD_STRING
Next i
stop_time = Now
elapsed_time = stop_time.Subtract(start_time)
Console.WriteLine(elapsed_time.TotalSeconds.ToString("0.000000"))
txt = ""
start_time = Now
For i As Long = 1 To num_trials
string_builder.Append(ADD_STRING)
Next i
txt = string_builder.ToString()
stop_time = Now
elapsed_time = stop_time.Subtract(start_time)
Console.WriteLine(elapsed_time.TotalSeconds.ToString("0.000000"))
End Sub
End class
|
0.015625
0.000000
2.41.StringReader StringWriter
2.41.1.StringWriter and StringReader
|
Imports System.IO
public class Test
public Shared Sub Main
Dim string_writer As New StringWriter()
string_writer.WriteLine("The quick brown fox")
string_writer.WriteLine("jumps over the lazy dog.")
Console.WriteLine(string_writer.ToString)
' Use a StringReader to read from the string.
Dim string_reader As New StringReader(string_writer.ToString)
string_writer.Close()
Console.WriteLine(string_reader.ReadLine())
Console.WriteLine(string_reader.ReadToEnd())
string_reader.Close()
End Sub
End class
|
The quick brown fox
jumps over the lazy dog.
The quick brown fox
jumps over the lazy dog.
2.42.Base64String
2.42.1.Convert string to base64string
|
Public Class Tester
Public Shared Sub Main
Dim quote As String = "AAAAA"
Dim quoteBytes As Byte() = System.Text.Encoding.UTF8.GetBytes(quote)
Dim quote64 As String = Convert.ToBase64String(quoteBytes)
Dim byteSet As Byte() = Convert.FromBase64String(quote64)
Dim result As String = System.Text.Encoding.UTF8.GetString(byteSet)
Console.WriteLine(quote & vbNewLine & quote64 & vbNewLine & result)
End Sub
End Class
|
AAAAA
QUFBQUE=
AAAAA
2.43.Wrapped Type
2.43.1.Wrapped Type
|
Option Strict On
Public Class WrappedType
Public Shared Sub Main()
Dim intVar As Integer = 100
Dim intType As Type = intVar.GetType()
Console.WriteLine(TypeName(intVar) & " = " & intType.FullName)
Dim stringVar As String = "This is a string."
Dim stringType As Type = stringVar.GetType()
Console.WriteLine(TypeName(stringVar) & " = " & stringType. FullName)
Dim boolVar As Boolean = True
Dim boolType As Type = boolVar.GetType()
Console.WriteLine(TypeName(boolVar) & " = " & boolType. FullName)
Dim singleVar As Single = 3.1417
Dim singleType As Type = singleVar.GetType()
Console.WriteLine(TypeName(singleVar) & " = " & singleType. FullName)
End Sub
End Class
|
Integer = System.Int32
String = System.String
Boolean = System.Boolean
Single = System.Single
|
2.43.2.Show .Net Command Types
|
|
Module Module1
Sub Main()
Dim A As Short
Dim B As Integer
Dim C As Int64
Dim D As Single
Dim E As Double
Dim F As Char
Console.WriteLine("A: {0} ", A.GetType().FullName)
Console.WriteLine("B: {0} ", B.GetType().FullName)
Console.WriteLine("C: {0} ", C.GetType().FullName)
Console.WriteLine("D: {0} ", D.GetType().FullName)
Console.WriteLine("E: {0} ", E.GetType().FullName)
Console.WriteLine("F: {0} ", F.GetType().FullName)
End Sub
End Module
|
|
|
A: System.Int16
B: System.Int32
C: System.Int64
D: System.Single
E: System.Double
F: System.Char
|
2.43.3.Use Equal to compare Data type
|
Imports System.Collections
public class Test
public Shared Sub Main
Dim s1 As New String("Hello")
Dim s2 As New String("Hello")
Console.WriteLine(s1.Equals(s2))
s1 = s2
Console.WriteLine(s1.Equals(s2))
Dim n1 As New Integer()
Dim n2 As New Integer()
n1 = 10
n2 = 10
Console.WriteLine(n1.Equals(n2))
n1 = 20
Console.WriteLine(n1.Equals(n2))
End Sub
End class
|
True
True
True
False
2.44.Number Function
2.44.1.CInt
|
public class Test
Public Const MAX_VALUES As Integer = CInt(123.45)
public Shared Sub Main
End Sub
End class
|
2.44.2.Fix
|
Option Strict On
Public Module FixTest
Public Sub Main()
Dim arr() As Decimal = {12.6d, 12.1d, -12.1d, -12.6d}
For Each num As Decimal In arr
Console.WriteLine("Fix({0}): {1}", num, Fix(num))
Console.WriteLine("Int({0}): {1}", num, Int(num))
Console.WriteLine()
Next
End Sub
End Module
|
Fix(12.6): 12
Int(12.6): 12
Fix(12.1): 12
Int(12.1): 12
Fix(-12.1): -12
Int(-12.1): -13
Fix(-12.6): -12
Int(-12.6): -13
2.44.3.Math.Round with IRR
|
Option Strict On
Public Module modMain
Public Sub Main()
Dim cashFlow() As Double = {-102450.55, -30967.12, 134.85, 82930.91, _
121766.18, 90345.58, 125093.16}
Dim guess As Double = .15
Console.WriteLine("{0}", Math.Round(IRR(cashFlow, guess)*100,1))
End Sub
End Module
|
31.1%
2.44.4.CInt: convert Hexadecimal in string to int
|
Option Strict On
Public Module modMain
Public Sub Main()
Dim convertedHex As Integer = CInt("&H75FF")
Console.WriteLine(convertedHex)
End Sub
End Module
|
30207
2.45.Data Type Convert
2.45.1.CLng: convert integer to long
|
Module Tester
Public Sub Main()
Dim iInteger As Integer = 5280
Dim lLong As Long
Dim bytByte As Byte
Dim sngSingle As Single
Dim dblDouble As Double
Dim decDecimal As Decimal
Console.WriteLine("Convert to a Long: {0}", CLng(iInteger) * CLng(iInteger))
End Sub
End Module
|
Convert to a Long: 27878400
2.45.2.CByte: convert to byte
|
Module Tester
Public Sub Main()
Dim iInteger As Integer = 5280
Dim lLong As Long
Dim bytByte As Byte
Dim sngSingle As Single
Dim dblDouble As Double
Dim decDecimal As Decimal
Console.Writeline("Convert to a Byte: {0}", CByte(iInteger))
End Sub
End Module
|
Unhandled Exception: System.OverflowException: Arithmetic operation resulted in an overflow.
at Tester.Main()
2.45.3.CSng: convert to Single
|
Module Tester
Public Sub Main()
Dim iInteger As Integer = 5280
Dim lLong As Long
Dim bytByte As Byte
Dim sngSingle As Single
Dim dblDouble As Double
Dim decDecimal As Decimal
Console.WriteLine("Convert to a Single: {0}", CSng(iInteger) / 3.4)
End Sub
End Module
|
Convert to a Single: 1552.94117647059
2.45.4.CDbl: convert to double
|
Module Tester
Public Sub Main()
Dim iInteger As Integer = 5280
Dim lLong As Long
Dim bytByte As Byte
Dim sngSingle As Single
Dim dblDouble As Double
Dim decDecimal As Decimal
Console.WriteLine("Convert to a Double: {0}", CDbl(iInteger) / 6.123)
End Sub
End Module
|
Convert to a Double: 862.322390984811
2.45.5.CDec: convert to decimal
|
Module Tester
Public Sub Main()
Dim iInteger As Integer = 5280
Dim lLong As Long
Dim bytByte As Byte
Dim sngSingle As Single
Dim dblDouble As Double
Dim decDecimal As Decimal
Console.WriteLine("Convert to a Decimal: {0}", CDec(iInteger) / 34)
End Sub
End Module
|
Convert to a Decimal: 155.29411764705882352941176471
2.45.6.Call Int64TryParse(String, NumberStyles, IFormatProvider,
Int32)
|
Imports System.Globalization
Module StringParsing
Public Sub Main()
Dim numericString As String
Dim styles As NumberStyles
numericString = "106779"
styles = NumberStyles.Integer
CallTryParse(numericString, styles)
numericString = "-30677"
styles = NumberStyles.None
CallTryParse(numericString, styles)
styles = NumberStyles.AllowLeadingSign
CallTryParse(numericString, styles)
numericString = "301677-"
CallTryParse(numericString, styles)
styles = styles Or NumberStyles.AllowTrailingSign
CallTryParse(numericString, styles)
numericString = "$10634"
styles = NumberStyles.Integer
CallTryParse(numericString, styles)
styles = NumberStyles.Integer Or NumberStyles.AllowCurrencySymbol
CallTryParse(numericString, styles)
numericString = "10345.00"
styles = NumberStyles.Integer Or NumberStyles.AllowDecimalPoint
CallTryParse(numericString, styles)
numericString = "10345.72"
styles = NumberStyles.Integer Or NumberStyles.AllowDecimalPoint
CallTryParse(numericString, styles)
numericString = "22,593"
styles = NumberStyles.Integer Or NumberStyles.AllowThousands
CallTryParse(numericString, styles)
numericString = "12E-01"
styles = NumberStyles.Integer Or NumberStyles.AllowExponent
CallTryParse(numericString, styles)
numericString = "12E03"
CallTryParse(numericString, styles)
numericString = "80c1"
CallTryParse(numericString, NumberStyles.HexNumber)
numericString = "0x80C1"
CallTryParse(numericString, NumberStyles.HexNumber)
End Sub
Private Sub CallTryParse(stringToConvert As String, styles AS NumberStyles)
Dim number As Long
Dim provider As CultureInfo
If CBool(styles And NumberStyles.AllowCurrencySymbol) Then
provider = CultureInfo.CurrentCulture
Else
provider = New CultureInfo("en-US")
End If
Dim result As Boolean = Int64.TryParse(stringToConvert, styles,provider, number)
If result Then
Console.WriteLine("Converted '{0}' to {1}.", stringToConvert, number)
Else
Console.WriteLine("Attempted conversion of '{0}' failed.", Convert.ToString(stringToConvert))
End If
End Sub
End Module
|
2.45.7.Convert a string into a 64-bit
signed integer value using the Int64.Parse(String) method
|
Module MainClass
Public Sub Main()
Convert(" 1")
End Sub
Private Sub Convert(value As String)
Try
Dim number As Long = Int64.Parse(value)
Console.WriteLine("Converted '{0}' to {1}.", value, number)
Catch e As FormatException
Console.WriteLine("Unable to convert '{0}'.", value)
Catch e As OverflowException
Console.WriteLine("'{0}' is out of range.", value)
End Try
End Sub
End Module
|
2.45.8.Convert.ToBase64CharArray() and
Convert.FromBase64CharArray methods
|
Imports System
Class Sample
Public Shared Sub Main()
Dim byteArray1(255) As Byte
Dim byteArray2(255) As Byte
Dim charArray(351) As Char
Dim charArrayLength As Integer
Dim x As Integer
For x = 0 To byteArray1.Length - 1
byteArray1(x) = CByte(x)
Console.Write("{0:X2} ", byteArray1(x))
Next x
charArrayLength = Convert.ToBase64CharArray( _
byteArray1, 0, byteArray1.Length, _
charArray, 0, _
Base64FormattingOptions.InsertLineBreaks)
Console.Write(charArrayLength)
Console.WriteLine(New [String](charArray))
byteArray2 = Convert.FromBase64CharArray(charArray, 0, charArrayLength)
End Sub
End Class
|
2.45.9.Converts the bit patterns of
UInt32 values to Byte arrays with the GetBytes method.
|
Imports System
Imports Microsoft.VisualBasic
Module GetBytesUInt32Demo
Sub GetBytesUInt32( argument As UInt32 )
Dim byteArray As Byte( ) = BitConverter.GetBytes( argument )
Console.WriteLine( BitConverter.ToString( byteArray ) )
End Sub
Sub Main( )
GetBytesUInt32( Convert.ToUInt32( 15 ) )
GetBytesUInt32( Convert.ToUInt32( &H100000 ) )
GetBytesUInt32( Convert.ToUInt32( Int32.MaxValue ) )
End Sub
End Module
|
2.45.10.Convert.ToString( non-numeric
types, IFormatProvider ).
|
Imports System
Imports System.Globalization
Imports Microsoft.VisualBasic
Public Class DummyProvider
Implements IFormatProvider
Public Function GetFormat( argType As Type ) As Object _
Implements IFormatProvider.GetFormat
Console.Write( "{0,-40}", argType.ToString( ) )
Return Nothing
End Function
End Class
Module MainClass
Sub Main( )
Dim provider As New DummyProvider( )
Dim converted As String
Dim Int32A As Integer = -1111111
Dim DoubleA As Double = 6.3
Dim ObjDouble As Object = CType( -98765.4321, Object )
Dim DayTimeA As DateTime = new DateTime( 2010, 9, 1, 13, 45, 0 )
Dim BoolA As Boolean = True
Dim StringA As String = "Qwerty"
Dim CharA As Char = "$"c
Dim TSpanA As TimeSpan = New TimeSpan( 0, 18, 0 )
Dim ObjOther As Object = CType( provider, Object )
converted = Convert.ToString( Int32A, provider )
Console.WriteLine( "Int32 {0}", converted )
converted = Convert.ToString( Int32A, provider )
Console.WriteLine( "Int32 {0}", converted )
converted = Convert.ToString( DoubleA, provider )
Console.WriteLine( "Double {0}", converted )
converted = Convert.ToString( ObjDouble, provider )
Console.WriteLine( "Object {0}", converted )
converted = Convert.ToString( DayTimeA, provider )
Console.WriteLine( "DateTime {0}", converted )
converted = Convert.ToString( BoolA, provider )
Console.WriteLine( "Boolean {0}", converted )
converted = Convert.ToString( StringA, provider )
Console.WriteLine( "String {0}", converted )
converted = Convert.ToString( CharA, provider )
Console.WriteLine( "Char {0}", converted )
converted = Convert.ToString( TSpanA, provider )
Console.WriteLine( "TimeSpan {0}", converted )
converted = Convert.ToString( ObjOther, provider )
Console.WriteLine( "Object {0}", converted )
End Sub
End Module
|
2.45.11.Create a hexadecimal value out
of range of the UInt64 type and Convert it back to a number.
|
Module Example
Public Sub Main()
Dim value As String = Convert.ToString(Long.MinValue, 16)
Try
Dim number As UInt64 = Convert.ToUInt64(value, 16)
Console.WriteLine("0x{0} converts to {1}.", value, number)
Catch e As OverflowException
Console.WriteLine("Unable to convert '0x{0}' to an unsigned long integer.",value)
End Try
End Sub
End Module
|
2.46.Matrix
2.46.1.Display a Matrix
|
' Quote from
'Visual Basic 2005 Cookbook Solutions for VB 2005 Programmers
'by Tim Patrick (Author), John Craig (Author)
'# Publisher: O'Reilly Media, Inc. (September 21, 2006)
'# Language: English
'# ISBN-10: 0596101775
'# ISBN-13: 978-0596101770
Public Class Tester
Public Shared Sub Main
Dim matrixA(,) As Double = { _
{4, 5, 6}, _
{7, 8, 9}, _
{3, 2, 1}}
Console.WriteLine(MatrixHelper.MakeDisplayable(matrixA))
End Sub
End Class
Module MatrixHelper
Public Function MakeDisplayable(ByVal sourceMatrix(,) As Double) As String
' ----- Prepare a multi-line string that shows the contents
' of a matrix, a 2D array.
Dim rows As Integer
Dim cols As Integer
Dim eachRow As Integer
Dim eachCol As Integer
Dim result As New System.Text.StringBuilder
' ----- Process all rows of the matrix, generating one
' output line per row.
rows = UBound(sourceMatrix, 1) + 1
cols = UBound(sourceMatrix, 2) + 1
For eachRow = 0 To rows - 1
' ----- Process each column of the matrix on a single
' row, separating values by commas.
If (eachRow > 0) Then result.AppendLine()
For eachCol = 0 To cols - 1
' ----- Add a single matrix element to the output.
If (eachCol > 0) Then result.Append(",")
result.Append(sourceMatrix(eachRow, eachCol).ToString)
Next eachCol
Next eachRow
' ----- Finished.
Return result.ToString
End Function
Public Function MakeDisplayable(ByVal sourceArray() As Double) As String
' ----- Present an array as multiple lines of output.
Dim result As New System.Text.StringBuilder
Dim scanValue As Double
For Each scanValue In sourceArray
result.AppendLine(scanValue.ToString)
Next scanValue
Return result.ToString
End Function
Public Function Inverse(ByVal sourceMatrix(,) As Double) As Double(,)
' ----- Build a new matrix that is the mathematical inverse
' of the supplied matrix. Multiplying a matrix and its
' inverse together will give the identity matrix.
Dim eachCol As Integer
Dim eachRow As Integer
Dim rowsAndCols As Integer
' ----- Determine the size of each dimension of the matrix.
' Only square matrices can be inverted.
If (UBound(sourceMatrix, 1) <> UBound(sourceMatrix, 2)) Then
Throw New Exception("Matrix must be square.")
End If
Dim rank As Integer = UBound(sourceMatrix, 1)
' ----- Clone a copy of the matrix (not just a new reference).
Dim workMatrix(,) As Double = _
CType(sourceMatrix.Clone, Double(,))
' ----- Variables used for backsolving.
Dim destMatrix(rank, rank) As Double
Dim rightHandSide(rank) As Double
Dim solutions(rank) As Double
Dim rowPivots(rank) As Integer
Dim colPivots(rank) As Integer
' ----- Use LU decomposition to form a triangular matrix.
workMatrix = FormLU(workMatrix, rowPivots, colPivots, rowsAndCols)
' ----- Backsolve the triangular matrix to get the inverted
' value for each position in the final matrix.
For eachCol = 0 To rank
rightHandSide(eachCol) = 1
BackSolve(workMatrix, rightHandSide, solutions, rowPivots, colPivots)
For eachRow = 0 To rank
destMatrix(eachRow, eachCol) = solutions(eachRow)
rightHandSide(eachRow) = 0
Next eachRow
Next eachCol
' ----- Return the inverted matrix result.
Return destMatrix
End Function
Public Function Determinant(ByVal sourceMatrix(,) As Double) As Double
' ----- Calculate the determinant of a matrix.
Dim result As Double
Dim pivots As Integer
Dim count As Integer
' ----- Only calculate the determinants of square matrices.
If (UBound(sourceMatrix, 1) <> UBound(sourceMatrix, 2)) Then
Throw New Exception( _
"Determinant only calculated for square matrices.")
End If
Dim rank As Integer = UBound(sourceMatrix, 1)
' ----- Make a copy of the matrix so we can work inside of it.
Dim workMatrix(rank, rank) As Double
Array.Copy(sourceMatrix, workMatrix, sourceMatrix.Length)
' ----- Use LU decomposition to form a triangular matrix.
Dim rowPivots(rank) As Integer
Dim colPivots(rank) As Integer
workMatrix = FormLU(workMatrix, rowPivots, colPivots, count)
' ----- Get the product at each of the pivot points.
result = 1
For pivots = 0 To rank
result *= workMatrix(rowPivots(pivots), colPivots(pivots))
Next pivots
' ----- Determine the sign of the result using LaPlace's formula.
result = (-1) ^ count * result
Return result
End Function
Public Function SimultEq(ByVal sourceEquations(,) As Double, _
ByVal sourceRHS() As Double) As Double()
' ----- Use matrices to solve simultaneous equations.
Dim rowsAndCols As Integer
' ----- The matrix must be square and the array size must match.
Dim rank As Integer = UBound(sourceEquations, 1)
If (UBound(sourceEquations, 2) <> rank) Or _
(UBound(sourceRHS, 1) <> rank) Then
Throw New Exception("Size problem for simultaneous equations.")
End If
' ----- Create some arrays for doing all of the work.
Dim coefficientMatrix(rank, rank) As Double
Dim rightHandSide(rank) As Double
Dim solutions(rank) As Double
Dim rowPivots(rank) As Integer
Dim colPivots(rank) As Integer
' ----- Make copies of the original matrices so we don't
' mess them up.
Array.Copy(sourceEquations, coefficientMatrix, sourceEquations.Length)
Array.Copy(sourceRHS, rightHandSide, sourceRHS.Length)
' ----- Use LU decomposition to form a triangular matrix.
coefficientMatrix = FormLU(coefficientMatrix, rowPivots, _
colPivots, rowsAndCols)
' ----- Find the unique solution for the upper-triangle.
BackSolve(coefficientMatrix, rightHandSide, solutions, _
rowPivots, colPivots)
' ----- Return the simultaneous equations result in an array.
Return solutions
End Function
Private Function FormLU(ByVal sourceMatrix(,) As Double, _
ByRef rowPivots() As Integer, ByRef colPivots() As Integer, _
ByRef rowsAndCols As Integer) As Double(,)
' ----- Perform an LU (lower and upper) decomposition of a matrix,
' a modified form of Gaussian elimination.
Dim eachRow As Integer
Dim eachCol As Integer
Dim pivot As Integer
Dim rowIndex As Integer
Dim colIndex As Integer
Dim bestRow As Integer
Dim bestCol As Integer
Dim rowToPivot As Integer
Dim colToPivot As Integer
Dim maxValue As Double
Dim testValue As Double
Dim oldMax As Double
Const Deps As Double = 0.0000000000000001
' ----- Determine the size of the array.
Dim rank As Integer = UBound(sourceMatrix, 1)
Dim destMatrix(rank, rank) As Double
Dim rowNorm(rank) As Double
ReDim rowPivots(rank)
ReDim colPivots(rank)
' ----- Make a copy of the array so we don't mess it up.
Array.Copy(sourceMatrix, destMatrix, sourceMatrix.Length)
' ----- Initialize row and column pivot arrays.
For eachRow = 0 To rank
rowPivots(eachRow) = eachRow
colPivots(eachRow) = eachRow
For eachCol = 0 To rank
rowNorm(eachRow) += Math.Abs(destMatrix(eachRow, eachCol))
Next eachCol
If (rowNorm(eachRow) = 0) Then
Throw New Exception("Cannot invert a singular matrix.")
End If
Next eachRow
' ----- Use Gauss-Jordan elimination on the matrix rows.
For pivot = 0 To rank - 1
maxValue = 0
For eachRow = pivot To rank
rowIndex = rowPivots(eachRow)
For eachCol = pivot To rank
colIndex = colPivots(eachCol)
testValue = Math.Abs(destMatrix(rowIndex, colIndex)) _
/ rowNorm(rowIndex)
If (testValue > maxValue) Then
maxValue = testValue
bestRow = eachRow
bestCol = eachCol
End If
Next eachCol
Next eachRow
' ----- Detect a singular, or very nearly singular, matrix.
If (maxValue = 0) Then
Throw New Exception("Singular matrix used for LU.")
ElseIf (pivot > 1) Then
If (maxValue < (Deps * oldMax)) Then
Throw New Exception("Non-invertible matrix used for LU.")
End If
End If
oldMax = maxValue
' ----- Swap row pivot values for the best row.
If (rowPivots(pivot) <> rowPivots(bestRow)) Then
rowsAndCols += 1
Swap(rowPivots(pivot), rowPivots(bestRow))
End If
' ----- Swap column pivot values for the best column.
If (colPivots(pivot) <> colPivots(bestCol)) Then
rowsAndCols += 1
Swap(colPivots(pivot), colPivots(bestCol))
End If
' ----- Work with the current pivot points.
rowToPivot = rowPivots(pivot)
colToPivot = colPivots(pivot)
' ----- Modify the remaining rows from the pivot points.
For eachRow = (pivot + 1) To rank
rowIndex = rowPivots(eachRow)
destMatrix(rowIndex, colToPivot) = _
-destMatrix(rowIndex, colToPivot) / _
destMatrix(rowToPivot, colToPivot)
For eachCol = (pivot + 1) To rank
colIndex = colPivots(eachCol)
destMatrix(rowIndex, colIndex) += _
destMatrix(rowIndex, colToPivot) * _
destMatrix(rowToPivot, colIndex)
Next eachCol
Next eachRow
Next pivot
' ----- Detect a non-invertible matrix.
If (destMatrix(rowPivots(rank), colPivots(rank)) = 0) Then
Throw New Exception("Non-invertible matrix used for LU.")
ElseIf (Math.Abs(destMatrix(rowPivots(rank), colPivots(rank))) / _
rowNorm(rowPivots(rank))) < (Deps * oldMax) Then
Throw New Exception("Non-invertible matrix used for LU.")
End If
' ----- Success. Return the LU triangular matrix.
Return destMatrix
End Function
Private Sub Swap(ByRef firstValue As Integer, ByRef secondValue As Integer)
' ----- Reverse the values of two reference integers.
Dim holdValue As Integer
holdValue = firstValue
firstValue = secondValue
secondValue = holdValue
End Sub
Private Sub BackSolve(ByVal sourceMatrix(,) As Double, _
ByVal rightHandSide() As Double, ByVal solutions() As Double, _
ByRef rowPivots() As Integer, ByRef colPivots() As Integer)
' ----- Solve an upper-right-triangle matrix.
Dim pivot As Integer
Dim rowToPivot As Integer
Dim colToPivot As Integer
Dim eachRow As Integer
Dim eachCol As Integer
Dim rank As Integer = UBound(sourceMatrix, 1)
' ----- Work through all pivot points. This section builds
' the "B" in the AX=B formula.
For pivot = 0 To (rank - 1)
colToPivot = colPivots(pivot)
For eachRow = (pivot + 1) To rank
rowToPivot = rowPivots(eachRow)
rightHandSide(rowToPivot) += _
sourceMatrix(rowToPivot, colToPivot) _
* rightHandSide(rowPivots(pivot))
Next eachRow
Next pivot
' ----- Now solve for each X using the general formula
' x(i) = (b(i) - summation(a(i,j)x(j)))/a(i,i)
For eachRow = rank To 0 Step -1
colToPivot = colPivots(eachRow)
rowToPivot = rowPivots(eachRow)
solutions(colToPivot) = rightHandSide(rowToPivot)
For eachCol = (eachRow + 1) To rank
solutions(colToPivot) -= _
sourceMatrix(rowToPivot, colPivots(eachCol)) _
* solutions(colPivots(eachCol))
Next eachCol
solutions(colToPivot) /= sourceMatrix(rowToPivot, colToPivot)
Next eachRow
End Sub
End Module
|
4,5,6
7,8,9
3,2,1
2.46.2.Invert a matrix
|
' Quote from
'Visual Basic 2005 Cookbook Solutions for VB 2005 Programmers
'by Tim Patrick (Author), John Craig (Author)
'# Publisher: O'Reilly Media, Inc. (September 21, 2006)
'# Language: English
'# ISBN-10: 0596101775
'# ISBN-13: 978-0596101770
Public Class Tester
Public Shared Sub Main
Dim matrixA(,) As Double = { _
{1, 3, 3}, _
{2, 4, 3}, _
{1, 3, 4}}
Dim matrixB(,) As Double = MatrixHelper.Inverse(matrixA)
Console.WriteLine(MatrixHelper.MakeDisplayable(matrixA) & _
vbNewLine & vbNewLine & "Inverse: " & _
vbNewLine & MatrixHelper.MakeDisplayable(matrixB))
End Sub
End Class
Module MatrixHelper
Public Function MakeDisplayable(ByVal sourceMatrix(,) As Double) As String
' ----- Prepare a multi-line string that shows the contents
' of a matrix, a 2D array.
Dim rows As Integer
Dim cols As Integer
Dim eachRow As Integer
Dim eachCol As Integer
Dim result As New System.Text.StringBuilder
' ----- Process all rows of the matrix, generating one
' output line per row.
rows = UBound(sourceMatrix, 1) + 1
cols = UBound(sourceMatrix, 2) + 1
For eachRow = 0 To rows - 1
' ----- Process each column of the matrix on a single
' row, separating values by commas.
If (eachRow > 0) Then result.AppendLine()
For eachCol = 0 To cols - 1
' ----- Add a single matrix element to the output.
If (eachCol > 0) Then result.Append(",")
result.Append(sourceMatrix(eachRow, eachCol).ToString)
Next eachCol
Next eachRow
' ----- Finished.
Return result.ToString
End Function
Public Function MakeDisplayable(ByVal sourceArray() As Double) As String
' ----- Present an array as multiple lines of output.
Dim result As New System.Text.StringBuilder
Dim scanValue As Double
For Each scanValue In sourceArray
result.AppendLine(scanValue.ToString)
Next scanValue
Return result.ToString
End Function
Public Function Inverse(ByVal sourceMatrix(,) As Double) As Double(,)
' ----- Build a new matrix that is the mathematical inverse
' of the supplied matrix. Multiplying a matrix and its
' inverse together will give the identity matrix.
Dim eachCol As Integer
Dim eachRow As Integer
Dim rowsAndCols As Integer
' ----- Determine the size of each dimension of the matrix.
' Only square matrices can be inverted.
If (UBound(sourceMatrix, 1) <> UBound(sourceMatrix, 2)) Then
Throw New Exception("Matrix must be square.")
End If
Dim rank As Integer = UBound(sourceMatrix, 1)
' ----- Clone a copy of the matrix (not just a new reference).
Dim workMatrix(,) As Double = _
CType(sourceMatrix.Clone, Double(,))
' ----- Variables used for backsolving.
Dim destMatrix(rank, rank) As Double
Dim rightHandSide(rank) As Double
Dim solutions(rank) As Double
Dim rowPivots(rank) As Integer
Dim colPivots(rank) As Integer
' ----- Use LU decomposition to form a triangular matrix.
workMatrix = FormLU(workMatrix, rowPivots, colPivots, rowsAndCols)
' ----- Backsolve the triangular matrix to get the inverted
' value for each position in the final matrix.
For eachCol = 0 To rank
rightHandSide(eachCol) = 1
BackSolve(workMatrix, rightHandSide, solutions, rowPivots, colPivots)
For eachRow = 0 To rank
destMatrix(eachRow, eachCol) = solutions(eachRow)
rightHandSide(eachRow) = 0
Next eachRow
Next eachCol
' ----- Return the inverted matrix result.
Return destMatrix
End Function
Public Function Determinant(ByVal sourceMatrix(,) As Double) As Double
' ----- Calculate the determinant of a matrix.
Dim result As Double
Dim pivots As Integer
Dim count As Integer
' ----- Only calculate the determinants of square matrices.
If (UBound(sourceMatrix, 1) <> UBound(sourceMatrix, 2)) Then
Throw New Exception( _
"Determinant only calculated for square matrices.")
End If
Dim rank As Integer = UBound(sourceMatrix, 1)
' ----- Make a copy of the matrix so we can work inside of it.
Dim workMatrix(rank, rank) As Double
Array.Copy(sourceMatrix, workMatrix, sourceMatrix.Length)
' ----- Use LU decomposition to form a triangular matrix.
Dim rowPivots(rank) As Integer
Dim colPivots(rank) As Integer
workMatrix = FormLU(workMatrix, rowPivots, colPivots, count)
' ----- Get the product at each of the pivot points.
result = 1
For pivots = 0 To rank
result *= workMatrix(rowPivots(pivots), colPivots(pivots))
Next pivots
' ----- Determine the sign of the result using LaPlace's formula.
result = (-1) ^ count * result
Return result
End Function
Public Function SimultEq(ByVal sourceEquations(,) As Double, _
ByVal sourceRHS() As Double) As Double()
' ----- Use matrices to solve simultaneous equations.
Dim rowsAndCols As Integer
' ----- The matrix must be square and the array size must match.
Dim rank As Integer = UBound(sourceEquations, 1)
If (UBound(sourceEquations, 2) <> rank) Or _
(UBound(sourceRHS, 1) <> rank) Then
Throw New Exception("Size problem for simultaneous equations.")
End If
' ----- Create some arrays for doing all of the work.
Dim coefficientMatrix(rank, rank) As Double
Dim rightHandSide(rank) As Double
Dim solutions(rank) As Double
Dim rowPivots(rank) As Integer
Dim colPivots(rank) As Integer
' ----- Make copies of the original matrices so we don't
' mess them up.
Array.Copy(sourceEquations, coefficientMatrix, sourceEquations.Length)
Array.Copy(sourceRHS, rightHandSide, sourceRHS.Length)
' ----- Use LU decomposition to form a triangular matrix.
coefficientMatrix = FormLU(coefficientMatrix, rowPivots, _
colPivots, rowsAndCols)
' ----- Find the unique solution for the upper-triangle.
BackSolve(coefficientMatrix, rightHandSide, solutions, _
rowPivots, colPivots)
' ----- Return the simultaneous equations result in an array.
Return solutions
End Function
Private Function FormLU(ByVal sourceMatrix(,) As Double, _
ByRef rowPivots() As Integer, ByRef colPivots() As Integer, _
ByRef rowsAndCols As Integer) As Double(,)
' ----- Perform an LU (lower and upper) decomposition of a matrix,
' a modified form of Gaussian elimination.
Dim eachRow As Integer
Dim eachCol As Integer
Dim pivot As Integer
Dim rowIndex As Integer
Dim colIndex As Integer
Dim bestRow As Integer
Dim bestCol As Integer
Dim rowToPivot As Integer
Dim colToPivot As Integer
Dim maxValue As Double
Dim testValue As Double
Dim oldMax As Double
Const Deps As Double = 0.0000000000000001
' ----- Determine the size of the array.
Dim rank As Integer = UBound(sourceMatrix, 1)
Dim destMatrix(rank, rank) As Double
Dim rowNorm(rank) As Double
ReDim rowPivots(rank)
ReDim colPivots(rank)
' ----- Make a copy of the array so we don't mess it up.
Array.Copy(sourceMatrix, destMatrix, sourceMatrix.Length)
' ----- Initialize row and column pivot arrays.
For eachRow = 0 To rank
rowPivots(eachRow) = eachRow
colPivots(eachRow) = eachRow
For eachCol = 0 To rank
rowNorm(eachRow) += Math.Abs(destMatrix(eachRow, eachCol))
Next eachCol
If (rowNorm(eachRow) = 0) Then
Throw New Exception("Cannot invert a singular matrix.")
End If
Next eachRow
' ----- Use Gauss-Jordan elimination on the matrix rows.
For pivot = 0 To rank - 1
maxValue = 0
For eachRow = pivot To rank
rowIndex = rowPivots(eachRow)
For eachCol = pivot To rank
colIndex = colPivots(eachCol)
testValue = Math.Abs(destMatrix(rowIndex, colIndex)) _
/ rowNorm(rowIndex)
If (testValue > maxValue) Then
maxValue = testValue
bestRow = eachRow
bestCol = eachCol
End If
Next eachCol
Next eachRow
' ----- Detect a singular, or very nearly singular, matrix.
If (maxValue = 0) Then
Throw New Exception("Singular matrix used for LU.")
ElseIf (pivot > 1) Then
If (maxValue < (Deps * oldMax)) Then
Throw New Exception("Non-invertible matrix used for LU.")
End If
End If
oldMax = maxValue
' ----- Swap row pivot values for the best row.
If (rowPivots(pivot) <> rowPivots(bestRow)) Then
rowsAndCols += 1
Swap(rowPivots(pivot), rowPivots(bestRow))
End If
' ----- Swap column pivot values for the best column.
If (colPivots(pivot) <> colPivots(bestCol)) Then
rowsAndCols += 1
Swap(colPivots(pivot), colPivots(bestCol))
End If
' ----- Work with the current pivot points.
rowToPivot = rowPivots(pivot)
colToPivot = colPivots(pivot)
' ----- Modify the remaining rows from the pivot points.
For eachRow = (pivot + 1) To rank
rowIndex = rowPivots(eachRow)
destMatrix(rowIndex, colToPivot) = _
-destMatrix(rowIndex, colToPivot) / _
destMatrix(rowToPivot, colToPivot)
For eachCol = (pivot + 1) To rank
colIndex = colPivots(eachCol)
destMatrix(rowIndex, colIndex) += _
destMatrix(rowIndex, colToPivot) * _
destMatrix(rowToPivot, colIndex)
Next eachCol
Next eachRow
Next pivot
' ----- Detect a non-invertible matrix.
If (destMatrix(rowPivots(rank), colPivots(rank)) = 0) Then
Throw New Exception("Non-invertible matrix used for LU.")
ElseIf (Math.Abs(destMatrix(rowPivots(rank), colPivots(rank))) / _
rowNorm(rowPivots(rank))) < (Deps * oldMax) Then
Throw New Exception("Non-invertible matrix used for LU.")
End If
' ----- Success. Return the LU triangular matrix.
Return destMatrix
End Function
Private Sub Swap(ByRef firstValue As Integer, ByRef secondValue As Integer)
' ----- Reverse the values of two reference integers.
Dim holdValue As Integer
holdValue = firstValue
firstValue = secondValue
secondValue = holdValue
End Sub
Private Sub BackSolve(ByVal sourceMatrix(,) As Double, _
ByVal rightHandSide() As Double, ByVal solutions() As Double, _
ByRef rowPivots() As Integer, ByRef colPivots() As Integer)
' ----- Solve an upper-right-triangle matrix.
Dim pivot As Integer
Dim rowToPivot As Integer
Dim colToPivot As Integer
Dim eachRow As Integer
Dim eachCol As Integer
Dim rank As Integer = UBound(sourceMatrix, 1)
' ----- Work through all pivot points. This section builds
' the "B" in the AX=B formula.
For pivot = 0 To (rank - 1)
colToPivot = colPivots(pivot)
For eachRow = (pivot + 1) To rank
rowToPivot = rowPivots(eachRow)
rightHandSide(rowToPivot) += _
sourceMatrix(rowToPivot, colToPivot) _
* rightHandSide(rowPivots(pivot))
Next eachRow
Next pivot
' ----- Now solve for each X using the general formula
' x(i) = (b(i) - summation(a(i,j)x(j)))/a(i,i)
For eachRow = rank To 0 Step -1
colToPivot = colPivots(eachRow)
rowToPivot = rowPivots(eachRow)
solutions(colToPivot) = rightHandSide(rowToPivot)
For eachCol = (eachRow + 1) To rank
solutions(colToPivot) -= _
sourceMatrix(rowToPivot, colPivots(eachCol)) _
* solutions(colPivots(eachCol))
Next eachCol
solutions(colToPivot) /= sourceMatrix(rowToPivot, colToPivot)
Next eachRow
End Sub
End Module
|
1,3,3
2,4,3
1,3,4
Inverse:
-3.5,1.5,1.5
2.5,-0.5,-1.5
-1,0,1
2.46.3.Calculate the determinant of an array
|
' Quote from
'Visual Basic 2005 Cookbook Solutions for VB 2005 Programmers
'by Tim Patrick (Author), John Craig (Author)
'# Publisher: O'Reilly Media, Inc. (September 21, 2006)
'# Language: English
'# ISBN-10: 0596101775
'# ISBN-13: 978-0596101770
Public Class Tester
Public Shared Sub Main
Dim matrixA(,) As Double = { _
{1, 2, 3}, _
{5, 4, 6}, _
{9, 7, 8}}
Dim determinant As Double = MatrixHelper.Determinant(matrixA)
Console.WriteLine(MatrixHelper.MakeDisplayable(matrixA) & _
vbNewLine & vbNewLine & "Determinant: " & _
determinant.ToString)
End Sub
End Class
Module MatrixHelper
Public Function MakeDisplayable(ByVal sourceMatrix(,) As Double) As String
' ----- Prepare a multi-line string that shows the contents
' of a matrix, a 2D array.
Dim rows As Integer
Dim cols As Integer
Dim eachRow As Integer
Dim eachCol As Integer
Dim result As New System.Text.StringBuilder
' ----- Process all rows of the matrix, generating one
' output line per row.
rows = UBound(sourceMatrix, 1) + 1
cols = UBound(sourceMatrix, 2) + 1
For eachRow = 0 To rows - 1
' ----- Process each column of the matrix on a single
' row, separating values by commas.
If (eachRow > 0) Then result.AppendLine()
For eachCol = 0 To cols - 1
' ----- Add a single matrix element to the output.
If (eachCol > 0) Then result.Append(",")
result.Append(sourceMatrix(eachRow, eachCol).ToString)
Next eachCol
Next eachRow
' ----- Finished.
Return result.ToString
End Function
Public Function MakeDisplayable(ByVal sourceArray() As Double) As String
' ----- Present an array as multiple lines of output.
Dim result As New System.Text.StringBuilder
Dim scanValue As Double
For Each scanValue In sourceArray
result.AppendLine(scanValue.ToString)
Next scanValue
Return result.ToString
End Function
Public Function Inverse(ByVal sourceMatrix(,) As Double) As Double(,)
' ----- Build a new matrix that is the mathematical inverse
' of the supplied matrix. Multiplying a matrix and its
' inverse together will give the identity matrix.
Dim eachCol As Integer
Dim eachRow As Integer
Dim rowsAndCols As Integer
' ----- Determine the size of each dimension of the matrix.
' Only square matrices can be inverted.
If (UBound(sourceMatrix, 1) <> UBound(sourceMatrix, 2)) Then
Throw New Exception("Matrix must be square.")
End If
Dim rank As Integer = UBound(sourceMatrix, 1)
' ----- Clone a copy of the matrix (not just a new reference).
Dim workMatrix(,) As Double = _
CType(sourceMatrix.Clone, Double(,))
' ----- Variables used for backsolving.
Dim destMatrix(rank, rank) As Double
Dim rightHandSide(rank) As Double
Dim solutions(rank) As Double
Dim rowPivots(rank) As Integer
Dim colPivots(rank) As Integer
' ----- Use LU decomposition to form a triangular matrix.
workMatrix = FormLU(workMatrix, rowPivots, colPivots, rowsAndCols)
' ----- Backsolve the triangular matrix to get the inverted
' value for each position in the final matrix.
For eachCol = 0 To rank
rightHandSide(eachCol) = 1
BackSolve(workMatrix, rightHandSide, solutions, rowPivots, colPivots)
For eachRow = 0 To rank
destMatrix(eachRow, eachCol) = solutions(eachRow)
rightHandSide(eachRow) = 0
Next eachRow
Next eachCol
' ----- Return the inverted matrix result.
Return destMatrix
End Function
Public Function Determinant(ByVal sourceMatrix(,) As Double) As Double
' ----- Calculate the determinant of a matrix.
Dim result As Double
Dim pivots As Integer
Dim count As Integer
' ----- Only calculate the determinants of square matrices.
If (UBound(sourceMatrix, 1) <> UBound(sourceMatrix, 2)) Then
Throw New Exception( _
"Determinant only calculated for square matrices.")
End If
Dim rank As Integer = UBound(sourceMatrix, 1)
' ----- Make a copy of the matrix so we can work inside of it.
Dim workMatrix(rank, rank) As Double
Array.Copy(sourceMatrix, workMatrix, sourceMatrix.Length)
' ----- Use LU decomposition to form a triangular matrix.
Dim rowPivots(rank) As Integer
Dim colPivots(rank) As Integer
workMatrix = FormLU(workMatrix, rowPivots, colPivots, count)
' ----- Get the product at each of the pivot points.
result = 1
For pivots = 0 To rank
result *= workMatrix(rowPivots(pivots), colPivots(pivots))
Next pivots
' ----- Determine the sign of the result using LaPlace's formula.
result = (-1) ^ count * result
Return result
End Function
Public Function SimultEq(ByVal sourceEquations(,) As Double, _
ByVal sourceRHS() As Double) As Double()
' ----- Use matrices to solve simultaneous equations.
Dim rowsAndCols As Integer
' ----- The matrix must be square and the array size must match.
Dim rank As Integer = UBound(sourceEquations, 1)
If (UBound(sourceEquations, 2) <> rank) Or _
(UBound(sourceRHS, 1) <> rank) Then
Throw New Exception("Size problem for simultaneous equations.")
End If
' ----- Create some arrays for doing all of the work.
Dim coefficientMatrix(rank, rank) As Double
Dim rightHandSide(rank) As Double
Dim solutions(rank) As Double
Dim rowPivots(rank) As Integer
Dim colPivots(rank) As Integer
' ----- Make copies of the original matrices so we don't
' mess them up.
Array.Copy(sourceEquations, coefficientMatrix, sourceEquations.Length)
Array.Copy(sourceRHS, rightHandSide, sourceRHS.Length)
' ----- Use LU decomposition to form a triangular matrix.
coefficientMatrix = FormLU(coefficientMatrix, rowPivots, _
colPivots, rowsAndCols)
' ----- Find the unique solution for the upper-triangle.
BackSolve(coefficientMatrix, rightHandSide, solutions, _
rowPivots, colPivots)
' ----- Return the simultaneous equations result in an array.
Return solutions
End Function
Private Function FormLU(ByVal sourceMatrix(,) As Double, _
ByRef rowPivots() As Integer, ByRef colPivots() As Integer, _
ByRef rowsAndCols As Integer) As Double(,)
' ----- Perform an LU (lower and upper) decomposition of a matrix,
' a modified form of Gaussian elimination.
Dim eachRow As Integer
Dim eachCol As Integer
Dim pivot As Integer
Dim rowIndex As Integer
Dim colIndex As Integer
Dim bestRow As Integer
Dim bestCol As Integer
Dim rowToPivot As Integer
Dim colToPivot As Integer
Dim maxValue As Double
Dim testValue As Double
Dim oldMax As Double
Const Deps As Double = 0.0000000000000001
' ----- Determine the size of the array.
Dim rank As Integer = UBound(sourceMatrix, 1)
Dim destMatrix(rank, rank) As Double
Dim rowNorm(rank) As Double
ReDim rowPivots(rank)
ReDim colPivots(rank)
' ----- Make a copy of the array so we don't mess it up.
Array.Copy(sourceMatrix, destMatrix, sourceMatrix.Length)
' ----- Initialize row and column pivot arrays.
For eachRow = 0 To rank
rowPivots(eachRow) = eachRow
colPivots(eachRow) = eachRow
For eachCol = 0 To rank
rowNorm(eachRow) += Math.Abs(destMatrix(eachRow, eachCol))
Next eachCol
If (rowNorm(eachRow) = 0) Then
Throw New Exception("Cannot invert a singular matrix.")
End If
Next eachRow
' ----- Use Gauss-Jordan elimination on the matrix rows.
For pivot = 0 To rank - 1
maxValue = 0
For eachRow = pivot To rank
rowIndex = rowPivots(eachRow)
For eachCol = pivot To rank
colIndex = colPivots(eachCol)
testValue = Math.Abs(destMatrix(rowIndex, colIndex)) _
/ rowNorm(rowIndex)
If (testValue > maxValue) Then
maxValue = testValue
bestRow = eachRow
bestCol = eachCol
End If
Next eachCol
Next eachRow
' ----- Detect a singular, or very nearly singular, matrix.
If (maxValue = 0) Then
Throw New Exception("Singular matrix used for LU.")
ElseIf (pivot > 1) Then
If (maxValue < (Deps * oldMax)) Then
Throw New Exception("Non-invertible matrix used for LU.")
End If
End If
oldMax = maxValue
' ----- Swap row pivot values for the best row.
If (rowPivots(pivot) <> rowPivots(bestRow)) Then
rowsAndCols += 1
Swap(rowPivots(pivot), rowPivots(bestRow))
End If
' ----- Swap column pivot values for the best column.
If (colPivots(pivot) <> colPivots(bestCol)) Then
rowsAndCols += 1
Swap(colPivots(pivot), colPivots(bestCol))
End If
' ----- Work with the current pivot points.
rowToPivot = rowPivots(pivot)
colToPivot = colPivots(pivot)
' ----- Modify the remaining rows from the pivot points.
For eachRow = (pivot + 1) To rank
rowIndex = rowPivots(eachRow)
destMatrix(rowIndex, colToPivot) = _
-destMatrix(rowIndex, colToPivot) / _
destMatrix(rowToPivot, colToPivot)
For eachCol = (pivot + 1) To rank
colIndex = colPivots(eachCol)
destMatrix(rowIndex, colIndex) += _
destMatrix(rowIndex, colToPivot) * _
destMatrix(rowToPivot, colIndex)
Next eachCol
Next eachRow
Next pivot
' ----- Detect a non-invertible matrix.
If (destMatrix(rowPivots(rank), colPivots(rank)) = 0) Then
Throw New Exception("Non-invertible matrix used for LU.")
ElseIf (Math.Abs(destMatrix(rowPivots(rank), colPivots(rank))) / _
rowNorm(rowPivots(rank))) < (Deps * oldMax) Then
Throw New Exception("Non-invertible matrix used for LU.")
End If
' ----- Success. Return the LU triangular matrix.
Return destMatrix
End Function
Private Sub Swap(ByRef firstValue As Integer, ByRef secondValue As Integer)
' ----- Reverse the values of two reference integers.
Dim holdValue As Integer
holdValue = firstValue
firstValue = secondValue
secondValue = holdValue
End Sub
Private Sub BackSolve(ByVal sourceMatrix(,) As Double, _
ByVal rightHandSide() As Double, ByVal solutions() As Double, _
ByRef rowPivots() As Integer, ByRef colPivots() As Integer)
' ----- Solve an upper-right-triangle matrix.
Dim pivot As Integer
Dim rowToPivot As Integer
Dim colToPivot As Integer
Dim eachRow As Integer
Dim eachCol As Integer
Dim rank As Integer = UBound(sourceMatrix, 1)
' ----- Work through all pivot points. This section builds
' the "B" in the AX=B formula.
For pivot = 0 To (rank - 1)
colToPivot = colPivots(pivot)
For eachRow = (pivot + 1) To rank
rowToPivot = rowPivots(eachRow)
rightHandSide(rowToPivot) += _
sourceMatrix(rowToPivot, colToPivot) _
* rightHandSide(rowPivots(pivot))
Next eachRow
Next pivot
' ----- Now solve for each X using the general formula
' x(i) = (b(i) - summation(a(i,j)x(j)))/a(i,i)
For eachRow = rank To 0 Step -1
colToPivot = colPivots(eachRow)
rowToPivot = rowPivots(eachRow)
solutions(colToPivot) = rightHandSide(rowToPivot)
For eachCol = (eachRow + 1) To rank
solutions(colToPivot) -= _
sourceMatrix(rowToPivot, colPivots(eachCol)) _
* solutions(colPivots(eachCol))
Next eachCol
solutions(colToPivot) /= sourceMatrix(rowToPivot, colToPivot)
Next eachRow
End Sub
End Module
|
1,2,3
5,4,6
9,7,8
Determinant: 15
2.46.4.Solve equations using matrices
|
' Quote from
'Visual Basic 2005 Cookbook Solutions for VB 2005 Programmers
'by Tim Patrick (Author), John Craig (Author)
'# Publisher: O'Reilly Media, Inc. (September 21, 2006)
'# Language: English
'# ISBN-10: 0596101775
'# ISBN-13: 978-0596101770
Public Class Tester
Public Shared Sub Main
Dim matrixA(,) As Double = { _
{1, 1, 1, 1}, _
{1, 5, 10, 25}, _
{0, 5, 10, 0}, _
{0, 0, 10, 25}}
Dim arrayB() As Double = {18, 223, 70, 200}
Dim arrayC() As Double = MatrixHelper.SimultEq(matrixA, arrayB)
Console.WriteLine(MatrixHelper.MakeDisplayable(matrixA) & _
vbNewLine & vbNewLine & MatrixHelper.MakeDisplayable(arrayB) & _
vbNewLine & vbNewLine & "Simultaneous Equations Solution:" & _
vbNewLine & MatrixHelper.MakeDisplayable(arrayC))
End Sub
End Class
Module MatrixHelper
Public Function MakeDisplayable(ByVal sourceMatrix(,) As Double) As String
' ----- Prepare a multi-line string that shows the contents
' of a matrix, a 2D array.
Dim rows As Integer
Dim cols As Integer
Dim eachRow As Integer
Dim eachCol As Integer
Dim result As New System.Text.StringBuilder
' ----- Process all rows of the matrix, generating one
' output line per row.
rows = UBound(sourceMatrix, 1) + 1
cols = UBound(sourceMatrix, 2) + 1
For eachRow = 0 To rows - 1
' ----- Process each column of the matrix on a single
' row, separating values by commas.
If (eachRow > 0) Then result.AppendLine()
For eachCol = 0 To cols - 1
' ----- Add a single matrix element to the output.
If (eachCol > 0) Then result.Append(",")
result.Append(sourceMatrix(eachRow, eachCol).ToString)
Next eachCol
Next eachRow
' ----- Finished.
Return result.ToString
End Function
Public Function MakeDisplayable(ByVal sourceArray() As Double) As String
' ----- Present an array as multiple lines of output.
Dim result As New System.Text.StringBuilder
Dim scanValue As Double
For Each scanValue In sourceArray
result.AppendLine(scanValue.ToString)
Next scanValue
Return result.ToString
End Function
Public Function Inverse(ByVal sourceMatrix(,) As Double) As Double(,)
' ----- Build a new matrix that is the mathematical inverse
' of the supplied matrix. Multiplying a matrix and its
' inverse together will give the identity matrix.
Dim eachCol As Integer
Dim eachRow As Integer
Dim rowsAndCols As Integer
' ----- Determine the size of each dimension of the matrix.
' Only square matrices can be inverted.
If (UBound(sourceMatrix, 1) <> UBound(sourceMatrix, 2)) Then
Throw New Exception("Matrix must be square.")
End If
Dim rank As Integer = UBound(sourceMatrix, 1)
' ----- Clone a copy of the matrix (not just a new reference).
Dim workMatrix(,) As Double = _
CType(sourceMatrix.Clone, Double(,))
' ----- Variables used for backsolving.
Dim destMatrix(rank, rank) As Double
Dim rightHandSide(rank) As Double
Dim solutions(rank) As Double
Dim rowPivots(rank) As Integer
Dim colPivots(rank) As Integer
' ----- Use LU decomposition to form a triangular matrix.
workMatrix = FormLU(workMatrix, rowPivots, colPivots, rowsAndCols)
' ----- Backsolve the triangular matrix to get the inverted
' value for each position in the final matrix.
For eachCol = 0 To rank
rightHandSide(eachCol) = 1
BackSolve(workMatrix, rightHandSide, solutions, rowPivots, colPivots)
For eachRow = 0 To rank
destMatrix(eachRow, eachCol) = solutions(eachRow)
rightHandSide(eachRow) = 0
Next eachRow
Next eachCol
' ----- Return the inverted matrix result.
Return destMatrix
End Function
Public Function Determinant(ByVal sourceMatrix(,) As Double) As Double
' ----- Calculate the determinant of a matrix.
Dim result As Double
Dim pivots As Integer
Dim count As Integer
' ----- Only calculate the determinants of square matrices.
If (UBound(sourceMatrix, 1) <> UBound(sourceMatrix, 2)) Then
Throw New Exception( _
"Determinant only calculated for square matrices.")
End If
Dim rank As Integer = UBound(sourceMatrix, 1)
' ----- Make a copy of the matrix so we can work inside of it.
Dim workMatrix(rank, rank) As Double
Array.Copy(sourceMatrix, workMatrix, sourceMatrix.Length)
' ----- Use LU decomposition to form a triangular matrix.
Dim rowPivots(rank) As Integer
Dim colPivots(rank) As Integer
workMatrix = FormLU(workMatrix, rowPivots, colPivots, count)
' ----- Get the product at each of the pivot points.
result = 1
For pivots = 0 To rank
result *= workMatrix(rowPivots(pivots), colPivots(pivots))
Next pivots
' ----- Determine the sign of the result using LaPlace's formula.
result = (-1) ^ count * result
Return result
End Function
Public Function SimultEq(ByVal sourceEquations(,) As Double, _
ByVal sourceRHS() As Double) As Double()
' ----- Use matrices to solve simultaneous equations.
Dim rowsAndCols As Integer
' ----- The matrix must be square and the array size must match.
Dim rank As Integer = UBound(sourceEquations, 1)
If (UBound(sourceEquations, 2) <> rank) Or _
(UBound(sourceRHS, 1) <> rank) Then
Throw New Exception("Size problem for simultaneous equations.")
End If
' ----- Create some arrays for doing all of the work.
Dim coefficientMatrix(rank, rank) As Double
Dim rightHandSide(rank) As Double
Dim solutions(rank) As Double
Dim rowPivots(rank) As Integer
Dim colPivots(rank) As Integer
' ----- Make copies of the original matrices so we don't
' mess them up.
Array.Copy(sourceEquations, coefficientMatrix, sourceEquations.Length)
Array.Copy(sourceRHS, rightHandSide, sourceRHS.Length)
' ----- Use LU decomposition to form a triangular matrix.
coefficientMatrix = FormLU(coefficientMatrix, rowPivots, _
colPivots, rowsAndCols)
' ----- Find the unique solution for the upper-triangle.
BackSolve(coefficientMatrix, rightHandSide, solutions, _
rowPivots, colPivots)
' ----- Return the simultaneous equations result in an array.
Return solutions
End Function
Private Function FormLU(ByVal sourceMatrix(,) As Double, _
ByRef rowPivots() As Integer, ByRef colPivots() As Integer, _
ByRef rowsAndCols As Integer) As Double(,)
' ----- Perform an LU (lower and upper) decomposition of a matrix,
' a modified form of Gaussian elimination.
Dim eachRow As Integer
Dim eachCol As Integer
Dim pivot As Integer
Dim rowIndex As Integer
Dim colIndex As Integer
Dim bestRow As Integer
Dim bestCol As Integer
Dim rowToPivot As Integer
Dim colToPivot As Integer
Dim maxValue As Double
Dim testValue As Double
Dim oldMax As Double
Const Deps As Double = 0.0000000000000001
' ----- Determine the size of the array.
Dim rank As Integer = UBound(sourceMatrix, 1)
Dim destMatrix(rank, rank) As Double
Dim rowNorm(rank) As Double
ReDim rowPivots(rank)
ReDim colPivots(rank)
' ----- Make a copy of the array so we don't mess it up.
Array.Copy(sourceMatrix, destMatrix, sourceMatrix.Length)
' ----- Initialize row and column pivot arrays.
For eachRow = 0 To rank
rowPivots(eachRow) = eachRow
colPivots(eachRow) = eachRow
For eachCol = 0 To rank
rowNorm(eachRow) += Math.Abs(destMatrix(eachRow, eachCol))
Next eachCol
If (rowNorm(eachRow) = 0) Then
Throw New Exception("Cannot invert a singular matrix.")
End If
Next eachRow
' ----- Use Gauss-Jordan elimination on the matrix rows.
For pivot = 0 To rank - 1
maxValue = 0
For eachRow = pivot To rank
rowIndex = rowPivots(eachRow)
For eachCol = pivot To rank
colIndex = colPivots(eachCol)
testValue = Math.Abs(destMatrix(rowIndex, colIndex)) _
/ rowNorm(rowIndex)
If (testValue > maxValue) Then
maxValue = testValue
bestRow = eachRow
bestCol = eachCol
End If
Next eachCol
Next eachRow
' ----- Detect a singular, or very nearly singular, matrix.
If (maxValue = 0) Then
Throw New Exception("Singular matrix used for LU.")
ElseIf (pivot > 1) Then
If (maxValue < (Deps * oldMax)) Then
Throw New Exception("Non-invertible matrix used for LU.")
End If
End If
oldMax = maxValue
' ----- Swap row pivot values for the best row.
If (rowPivots(pivot) <> rowPivots(bestRow)) Then
rowsAndCols += 1
Swap(rowPivots(pivot), rowPivots(bestRow))
End If
' ----- Swap column pivot values for the best column.
If (colPivots(pivot) <> colPivots(bestCol)) Then
rowsAndCols += 1
Swap(colPivots(pivot), colPivots(bestCol))
End If
' ----- Work with the current pivot points.
rowToPivot = rowPivots(pivot)
colToPivot = colPivots(pivot)
' ----- Modify the remaining rows from the pivot points.
For eachRow = (pivot + 1) To rank
rowIndex = rowPivots(eachRow)
destMatrix(rowIndex, colToPivot) = _
-destMatrix(rowIndex, colToPivot) / _
destMatrix(rowToPivot, colToPivot)
For eachCol = (pivot + 1) To rank
colIndex = colPivots(eachCol)
destMatrix(rowIndex, colIndex) += _
destMatrix(rowIndex, colToPivot) * _
destMatrix(rowToPivot, colIndex)
Next eachCol
Next eachRow
Next pivot
' ----- Detect a non-invertible matrix.
If (destMatrix(rowPivots(rank), colPivots(rank)) = 0) Then
Throw New Exception("Non-invertible matrix used for LU.")
ElseIf (Math.Abs(destMatrix(rowPivots(rank), colPivots(rank))) / _
rowNorm(rowPivots(rank))) < (Deps * oldMax) Then
Throw New Exception("Non-invertible matrix used for LU.")
End If
' ----- Success. Return the LU triangular matrix.
Return destMatrix
End Function
Private Sub Swap(ByRef firstValue As Integer, ByRef secondValue As Integer)
' ----- Reverse the values of two reference integers.
Dim holdValue As Integer
holdValue = firstValue
firstValue = secondValue
secondValue = holdValue
End Sub
Private Sub BackSolve(ByVal sourceMatrix(,) As Double, _
ByVal rightHandSide() As Double, ByVal solutions() As Double, _
ByRef rowPivots() As Integer, ByRef colPivots() As Integer)
' ----- Solve an upper-right-triangle matrix.
Dim pivot As Integer
Dim rowToPivot As Integer
Dim colToPivot As Integer
Dim eachRow As Integer
Dim eachCol As Integer
Dim rank As Integer = UBound(sourceMatrix, 1)
' ----- Work through all pivot points. This section builds
' the "B" in the AX=B formula.
For pivot = 0 To (rank - 1)
colToPivot = colPivots(pivot)
For eachRow = (pivot + 1) To rank
rowToPivot = rowPivots(eachRow)
rightHandSide(rowToPivot) += _
sourceMatrix(rowToPivot, colToPivot) _
* rightHandSide(rowPivots(pivot))
Next eachRow
Next pivot
' ----- Now solve for each X using the general formula
' x(i) = (b(i) - summation(a(i,j)x(j)))/a(i,i)
For eachRow = rank To 0 Step -1
colToPivot = colPivots(eachRow)
rowToPivot = rowPivots(eachRow)
solutions(colToPivot) = rightHandSide(rowToPivot)
For eachCol = (eachRow + 1) To rank
solutions(colToPivot) -= _
sourceMatrix(rowToPivot, colPivots(eachCol)) _
* solutions(colPivots(eachCol))
Next eachCol
solutions(colToPivot) /= sourceMatrix(rowToPivot, colToPivot)
Next eachRow
End Sub
End Module
|
1,1,1,1
1,5,10,25
0,5,10,0
0,0,10,25
18
223
70
200
Simultaneous Equations Solution:
3
4
5
6
2.47.WeakReference
2.47.1.WeakReference
|
public class Test
public Shared Sub Main
Dim wr As WeakReference
Dim obj As New Person()
wr = New WeakReference(obj)
End Sub
End class
Public Class Person
Implements IDisposable
Private Disposed As Boolean = False
Public Overloads Sub Dispose() Implements IDisposable.Dispose
Dispose(True)
System.GC.SuppressFinalize(Me)
End Sub
Protected Overloads Sub Dispose(ByVal disposing As Boolean)
Me.Disposed = True
End Sub
Protected Overrides Sub finalize()
Console.WriteLine("In Person Finalize")
MyBase.Finalize()
Me.Dispose(False)
End Sub
End Class
|
In Person Finalize
2.48.Nullable
2.48.1.Assigning Nothing to a variable
sets it to the default value for its declared type.
|
Module Module1
Public Structure testStruct
Public name As String
Public number As Short
End Structure
Sub Main()
Dim ts As testStruct
Dim i As Integer
Dim b As Boolean
' The following statement sets ts.name to "" and ts.number to 0.
ts = Nothing
' The following statements set i to 0 and b to False.
i = Nothing
b = Nothing
Console.WriteLine("ts.name: " & ts.name)
Console.WriteLine("ts.number: " & ts.number)
Console.WriteLine("i: " & i)
Console.WriteLine("b: " & b)
End Sub
End Module
|
2.48.2.Nullable(Of T).GetValueOrDefault
methods.
|
Imports System
Class Sample
Public Shared Sub Main()
Dim mySingle As Nullable(Of System.Single) = 12.34F
Dim yourSingle As Nullable(Of System.Single) = - 1.0F
Console.WriteLine(mySingle)
Console.WriteLine(yourSingle)
yourSingle = mySingle.GetValueOrDefault()
Console.WriteLine(mySingle)
Console.WriteLine(yourSingle)
mySingle = Nothing
yourSingle = mySingle.GetValueOrDefault()
Console.WriteLine(mySingle)
Console.WriteLine(yourSingle)
mySingle = 12.34F
yourSingle = - 1.0F
Console.WriteLine(mySingle)
Console.WriteLine(yourSingle)
yourSingle = mySingle.GetValueOrDefault(- 222.22F)
Console.WriteLine(mySingle)
Console.WriteLine(yourSingle)
mySingle = Nothing
yourSingle = mySingle.GetValueOrDefault(- 333.33F)
Console.WriteLine(mySingle)
Console.WriteLine(yourSingle)
End Sub
End Class
|
2.48.3.If the variable is of a
reference type, a value of Nothing is a null value.
|
Module Module1
Sub Main()
Dim testObject As Object
testObject = Nothing
Dim tc As New TestClass
tc = Nothing
End Sub
Class TestClass
Public field1 As Integer
End Class
End Module
|
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