Visual Basic 6 Black Book:The Visual Basic Language
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There’s a wide range of data types, so we’ll use a table here. The Visual Basic variable types appear in Table 3.1 for reference, making selecting the right type a little easier (note that although Visual Basic lists a Decimal variable type, that type is not yet actually supported). We also include the literal suffix symbols for numeric values in Table 3.1—those are the suffixes you can add to the end of values or variables to tell Visual Basic their type, like strUserFormatString$.
Table 3.1 Variable types.

Variable Type
Bytes Of Storage
Literal Suffix
Range

Boolean
2
N/A
True, False

Byte
1
N/A
0 to 255

Currency
8
@
-922,337,203,685,477.5808 to 922,337,203,685,477.5807

Date
8
#…#
1 January 100 to 31 December 9999 and times from 0:00:00 to 23:59:59

Decimal
12
N/A
-79,228,162,514,264,337,593,543,950,335 to 79,228,162,514,264,337,593,543,950,335

Double
8
#
-1.79769313486232E308 to -4.94065645841247E-324 for negative values and from 4.94065645841247E-324 to 1.79769313486232E308 for positive values

Integer
2
%
-32,768 to 32,767

Long
4
&
-2,147,483,648 to 2,147,483,647

Object
4
N/A
N/A

Single
4
!
-3.402823E38 to -1.401298E-45 for negative values and from 1.401298E-45 to 3.402823E38 for positive values

String
N/A
$
A variable-length string can contain up to approximately 2 billion characters; a fixed-length string can contain 1 to approximately 64K characters

User-defined data type
N/A
N/A
N/A

Variant
N/A
N/A
N/A

As you can see in Table 3.1, Visual Basic has a large number of data formats. The Variant type deserves special mention, because it’s the default variable type. If you don’t declare a type for a variable, it is made a variant:


Private Sub Command1_Click()
Dim NumberTrains
...
End Sub


In this case, the variable NumberTrains is a variant, which means it can take any type of data. For example, here we place an integer value into NumberTrains (note that we specify that 5 is an integer by using the percent sign [%] suffix as specified in Table 3.1):


Private Sub Command1_Click()
Dim NumberTrains
NumberTrains = 5%
End Sub


We could have used other data types as well; here, for example, we place a string into NumberTrains:


Private Sub Command1_Click()
Dim NumberTrains
NumberTrains = "Five"
End Sub


And here we use a floating point value (! is the suffix for single values):



Private Sub Command1_Click()
Dim NumberTrains
NumberTrains = 5.00!
End Sub


Be careful of variants, however—they waste time because Visual Basic has to translate them into other data types before using them, and they also take up more space than other data types.

Converting Between Data Types
Visual Basic supports a number of ways of converting from one type of variable to another—in fact, that’s one of the strengths of the language. The possible conversion statements and procedures appear in Table 3.2.

Table 3.2 Visual Basic data conversion functions.

To Do This
Use This

ANSI value to string
Chr

String to lowercase or uppercase
Format, LCase, UCase

Date to serial number
DateSerial, DateValue

Decimal number to other bases
Hex, Oct

Number to string
Format, Str

One data type to another
CBool, CByte, CCur, CDate, CDbl, CDec, CInt, CLng, CSng, CStr, CVar, CVErr, Fix, Int

Date to day, month, weekday, or year
Day, Month, Weekday, Year

Time to hour, minute, or second
Hour, Minute, Second

String to ASCII value
Asc

String to number
Val

Time to serial number
TimeSerial, TimeValue


TIP:  Note that you can cast variables from one type to another in Visual Basic using the functions CBool(), CByte(), and so on.

Setting Variable Scope
You’ve just finished creating a new dialog box in your greeting card program, and it’s a beauty. However, you realize there’s a problem: the user enters the new number of balloons to display the greeting card in TextBox1 of the dialog box, but how do you read that value in the rest of the program when the user closes the dialog box?
It’s tempting to set up a global variable, intNumberBalloons, which you fill in the dialog box when the user clicks on the OK button. That way, you’ll be able to use that variable in the rest of the program when the dialog box is closed. But in this case, you should resist the temptation to create a global variable—it’s much better to refer to the text in the text box this way (assuming the name of the dialog form you’ve created is Dialog):


intNumberBalloons = Dialog.TextBox1.Text






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