Podstawy programowania

(3)

dr Jerzy Bartoszek

[e-mail]

[e-mail].p

l

Przykład procedury

Module Module1
Sub Main()
DisplayMessage("Hello from Visual Basic")
End Sub

Sub DisplayMessage(ByVal strText As

String)

System.Console.WriteLine(strText)
End Sub

End Module

Schemat definiowania

procedury

Sub name [(arglist)]

[ statements ]
[ Exit Sub ]
[ statements ]

End Sub

Przykład funkcji

Module Module1
Sub Main()

Dim intValue As Integer = 2
System.Console.WriteLine("

{0}

+

{1}

=

{2}

",

intValue, _
intValue, Add(intValue, intValue))

End Sub

Function Add(ByVal i1 As Integer, ByVal i2 As

Integer)_

As Long

Return

i1 + i2

End Function

End Module

Schemat definiowania

funkcji

Function name [(arglist)] As type

[ statements ]
[ Exit Function ]

[ statements ]

End Sub

Musi zawierać

return expr

.

Przekazywanie parametrów

• ByVal

- przez wartość. Stosowany

dla parametrów „wejściowych”. Do

procedury/funkcji pzrekazywana

jest

wartość

parametru aktualnego.

• ByRef

– przez referencję.

Stosowany dla parametrów

wyjściowych. Do procedury/funkcji

przekazywana jest

referencja

do

parametru aktualnego (który

musi

być zmienną

).

Przykład przekazywania

parametrów

Sub TestFunc(

ByVal x

As Integer,

ByRef y

As _
Integer,

ByRef z

As Integer)

  x += 1

  y += 1

  z = 5

End Sub
Dim a = 1, b = 1, c As Integer   
' c set to zero by default 

TestFunc(

a, b, c

)

Console.WriteLine("{0} {1} {2}", a, b, c)
'

1

 

2 5

Wartości opcjonalne

parametrów

Module Module1
Sub Main()

DisplayMessage()

End Sub
Sub DisplayMessage(

Optional ByVal

strText _ As String

= "Hello from Visual

Basic"

)

System.Console.WriteLine(strText)
End Sub
End Module

Przykład parametru

opcjonalnego

' Optional parameters must be listed

last and must have a default value

Sub SayHello(ByVal name As String, _

Optional ByVal

prefix

As String =

"")

  Console.WriteLine("Greetings, " &

prefix & " " & name)

End Sub
SayHello("Nowak", "Dr.")
SayHello("Kowalski")

Zmienna liczba parametrów

Module Module1
Sub Main()

DisplayMessage("First message:",

"Hi"

)

DisplayMessage("Second message:",

"Hello", "there"

)

Dim TextArray() As String = {"Hello", "from", "Visual", _
"Basic"}
DisplayMessage("Third message:",

TextArray

)

End Sub
Sub DisplayMessage(ByVal Title As String,

ByVal ParamArray _

MessageText() As String

)

Dim intLoopIndex As Integer
System.Console.WriteLine(Title)
For intLoopIndex = 0 To

UBound(MessageText)

System.Console.WriteLine(MessageText(intLoopIndex))
Next intLoopIndex

End Sub
End Module

Zmienne statyczne

Module Module1
Sub Main()

Dim intLoopIndex As Integer, intValue = 0
For intLoopIndex = 0 To 4

intValue =

Counter()

Next intLoopIndex
System.Console.WriteLine(

intValue

)

End Sub
Function Counter() As Integer

Dim intCountValue As Integer

intCountValue += 1

Return

intCountValue

End Function
End Module

Przykład zmiennej liczby

parametrów

Function

Sum

(ByVal

ParamArray nums

_
As Integer()) As Integer

 

Sum

= 0 

  For Each i As Integer In nums

   

Sum

+= i

  Next

End Function  

Dim total As Integer = Sum(

4, 3, 2, 1

)

Zmienne statyczne

Module Module1
Sub Main()

Dim intLoopIndex As Integer, intValue = 0
For intLoopIndex = 0 To 4

intValue =

Counter()

Next intLoopIndex
System.Console.WriteLine(

intValue

)

End Sub
Function Counter() As Integer

Static

intCountValue As Integer

intCountValue += 1

Return

intCountValue

End Function
End Module

Zakres (ang. scope)

widoczności

• Block

scope

- available only within

the code block in which it is declared

• Procedure

scope

- available only

within the procedure in which it is

declared

• Module

scope

- available to all code

within the module, class, or

structure in which it is declared

• Namespace

scope

- available to all

code in the namespace

Obsługa wyjątków

Try

[ tryStatements ]

[Catch [ exception1 [ As type1 ] ] [ When

expression1 ]
catchStatements1 [Exit Try] ]

[Catch [ exception2 [ As type2 ] ] [When expression2 ]

catchStatements2 [ Exit Try ] ]

…
[Catch [ exceptionn [ As typen ] ] [ When

expressionn ]

catchStatementsn ] [ Exit Try ] ]
[ Finally

[ finallyStatements ]

End Try

Przykład obsługi wyjątków

Sub Main()
Dim int3 As Integer

Try

int3 = …
System.Console.WriteLine("The answer is {0}", int3)

Catch

e As System.ArgumentOutOfRangeException

System.Console.WriteLine("Exception: Argument out of" _
& " range!")

Catch

e As System.ArgumentException

System.Console.WriteLine("Exception: Invalid argument„ _
& " value!")

Catch

e As Exception

System.Console.WriteLine("Exception occurred!")

End Try

End Sub

Przykład z when

Sub Main()

Dim int1 = 0, int2 = 1, int3 As Integer

Try int3 = int2 / int1

System.Console.WriteLine( _
"The answer is {0}", int3)

Catch

When Err.Number = 6

System.Console.WriteLine( _
"Exception: Arithmetic overflow!")

End Try
End Sub

Przykład z finally

Sub Main()

…

Try

…

Catch e As System.ArgumentOutOfRangeException

System.Console.WriteLine("Exception: Argument out of" _
& " range!")
…

Catch e As Exception

System.Console.WriteLine("Exception occurred!")

Finally

System.Console.WriteLine("Execution of sensitive code " & _
"is complete")

End Try
End Sub

Generowanie wyjątków

Sub Main()
Try

…

Throw New OverflowException()

…

Catch e As OverflowException
System.Console.WriteLine(e.Message)

…

End Try
End Sub