Visual Basic/Data Types
Data types in Visual Basic can be divided into three groups:
- Native: Types that are understood directly by the Visual Basic compiler without assistance from the programmer
- User-defined: commonly referred to by the initials UDT, meaning User defined Type, these correspond to Pascal records or C structs
- Classes: the basis for object oriented programming in Visual Basic. Classes include forms, add-ins, and database designers.
If you are using Excel VBA, remember that VBA is essentially VB6, and hence those rules apply.
Built in Types
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This section applies to version 7 and newer (i.e, VB.NET) of Visual Basic.
The built in types are:
| Visual Basic type | Common language runtime type structure | Nominal storage allocation | Value range |
|---|---|---|---|
| Boolean | Boolean | Depends on implementing platform | True or False
|
| Byte | Byte | 1 byte | 0 through 255 (unsigned) |
| Char(single character) | Char | 2 bytes | 0 through 65535 (unsigned) |
| Date | DateTime | 8 bytes | 0:00:00 (midnight) on January 1, 0001 through 11:59:59 PM on December 31, 9999 |
| Decimal | Decimal | 16 bytes | 0 through +/-79,228,162,514,264,337,593,543,950,335 (+/-7.9...E+28) † with no decimal point; 0 through +/-7.9228162514264337593543950335 with 28 places to the right of the decimal;
smallest nonzero number is +/-0.0000000000000000000000000001 (+/-1E-28) † |
| Double(double-precision floating-point) | Double | 8 bytes | -1.79769313486231570E+308 through -4.94065645841246544E-324 † for negative values;
4.94065645841246544E-324 through 1.79769313486231570E+308 † for positive values |
| Integer | Int32 | 4 bytes | -2,147,483,648 through 2,147,483,647 (signed) |
| Long(long integer) | Int64 | 8 bytes | -9,223,372,036,854,775,808 through 9,223,372,036,854,775,807 (9.2...E+18 †) (signed) |
| Object | Object(class) | 4 bytes on 32-bit platform
8 bytes on 64-bit platform |
Any type can be stored in a variable of type Object
|
| SByte | SByte | 1 byte | -128 through 127 (signed) |
| Short(short integer) | Int16 | 2 bytes | -32,768 through 32,767 (signed) |
| Single(single-precision floating-point) | Single | 4 bytes | -3.4028235E+38 through -1.401298E-45 † for negative values;
1.401298E-45 through 3.4028235E+38 † for positive values |
| String(variable-length) | String(class) | Depends on implementing platform | 0 to approximately 2 billion Unicode characters |
| UInteger | UInt32 | 4 bytes | 0 through 4,294,967,295 (unsigned) |
| ULong | UInt64 | 8 bytes | 0 through 18,446,744,073,709,551,615 (1.8...E+19 †) (unsigned) |
| User-Defined(structure) | (inherits from ValueType) | Depends on implementing platform | Each member of the structure has a range determined by its data type and independent of the ranges of the other members |
| UShort | UInt16 | 2 bytes | 0 through 65,535 (unsigned) |
Byte, Integer & Long
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This section applies to version 6 and older of Visual Basic, an older version.
Example:
Dim a as Byte
Dim i as Integer
Dim x,y as Long 'Define two variables. Note that only the last variable will be a long integer.
Now those variables will only be capable of storing integer values (without decimal). Long integers can store a number with a bigger range of value than integers but they occupy a bigger space of RAM.
| Type | Storage | Range of Values |
|---|---|---|
| Byte | 1 byte | 0 to 254 |
| Integer | 2 bytes | -32,768 to 32,767 |
| Long | 4 bytes | -2,147,483,648 to 2,147,483,647 |
Some functions you need to know: Int()
Int() converts a decimal value into an integer value:
Dim i as Integer
i=Int(3.9)
Print i 'Prints 3
Single & Double
[edit | edit source]These data types can store decimal values. "Double" compared to "Single" is similar to the "Long" compared to "Integer":
| Type | Storage | Range of Values |
|---|---|---|
| Single | 4 bytes | -3.402823E+38 to -1.401298E-45 for negative values
1.401298E-45 to 3.402823E+38 for positive values. |
| Double | 8 bytes | -1.79769313486232E+308 to -4.94065645841247E-324 for negative values
4.94065645841247E-324 to 1.79769313486232E+308 for positive values. |
Some useful functions: Round()
Round() rounds off a decimal to a certain number of decimal digits that the programmer wants. The first argument should be a decimal value which you want to round off. The second argument specifies the number of decimal digits you want, for example:
Dim pi as Double
pi=3.141592653589
pi=Round(pi,2) 'Rounds off 3.141592653589 to only two decimal digits
Print pi 'Prints 3.14
String
[edit | edit source]A string is an array of characters. As an example:
Dim a As String
a = "This is a string"
Strings can be concatenated (connected together to form a new string) using the "&" operator. For example,
dim b as String
b = "Wiki" & "book" & "s"
Print b 'Prints "Wikibooks"
A normal string variable occupies 10 bytes of RAM, plus the string's size, and can hold up to 2 billion characters!
Some frequently used built-in string constants: vbTab, vbCrLf
vbTab contains a string that does the same thing as the Tab key on your keyboard, while vbCrLf creates a character return and a line feed(similar to the Enter key):
Print "Jack:" & vbTab & "1 pie" & vbCrLf & "me:" & vbTab & "10 pies"
Will print:
Jack: 1 pie me: 10 pies
To include special characters and quotation marks in the strings, the Chr() function may be used:
Dim a As String
Print "A quotation mark: [" & Chr(34) & "]"
a = "Replace 'apostrophes' for quotation marks"
Replace( a, "'", Chr(34) )
Print a
Some string functions: Str(),Val(),inStr(),Mid(),Replace(),Trim()
In fact there are tons of built-in string manipulation functions available. But right now, I'll just introduce two: Str() and Val().
Str() converts any numerical value into a string value while Val() converts a string value into a numerical value(only when it's convertible).
Dim MyString As String
Dim MyNumber As Single
MyString=Str(300) 'converts a number into a string
MyNumber=Val("300") 'converts a string into a number
Even if you don't do the conversion, you will not end up getting Type Mismatch Errors. However, it is considered better to use explicit type conversions, because it is easier to debug.
Even if you do be prepared for next to impossible to debug problems caused by VB refusing to convert something and refusing to tell you what the heck it is. VB is extremely touchy and raises an exception at the least expected times.
Structure
[edit | edit source]An example definition of a structured type:
Type E2Point
x As Double
y As Double
End Type
Sub Test()
Dim MyPoint As E2Point
Dim MyPoint2 As E2Point
MyPoint.x = 4
MyPoint.y = -5
MyPoint2 = MyPoint 'Make a copy
MyPoint2.x = 3
MyPoint2.y = -6
Debug.Print MyPoint.x, MyPoint.y '4, -5: not overriden with 3 and -6
Debug.Print TypeOf MyPoint Is E2Point 'True
Debug.Print TypeOf MyPoint Is Object 'False
End Sub
The type has to be defined outside of a procedure.
A variable of a structure type is not an object.
Links:
- Type Statement, Office 2013, msdn.microsoft.com
- Type Statement at Visual Basic for Applications Reference, msdn.microsoft.com
Enumeration
[edit | edit source]An example definition of an enumerated type:
Enum Colors
Red '=0
Green '=1
Blue '=2
End Enum
Enum Colors2
Red2 = 1
Green2 '=2
Blue2 '=3
End Enum
Sub Test()
Debug.Print Red, Green, Blue
Debug.Print Red2, Green2, Blue2
Dim MyVar As Colors 'Ends up being typed as Long
MyVar = 8 'Does not lead to an error: no restriction on values
End Sub
Links:
- Enum Statement, Office 2013, msdn.microsoft.com
- Enum Statement at Visual Basic for Applications Reference, msdn.microsoft.com
Type Test
[edit | edit source]To find out about the type of a variable, you can use "TypeOf ... Is ..." test. The tested types can only be object types and structure types, but the test can be applied to any variable, whether typed as an integer, a string or an object.
An example of TypeOf in Excel:
Set MyVar = Selection
Debug.Print "Selection is an object: " & TypeOf MyVar Is Object
Debug.Print "Selection is a range: " & TypeOf MyVar Is Range
Debug.Print "Sheets is of type Sheets: " & TypeOf Sheets Is Sheets
MyStr = "Hello"
Debug.Print "Text is an object: " & TypeOf MyStr Is Object
If TypeOf MyVar Is Range Then
Set MyCells = MyVar.Cells
End If
An example test with a "Select Case True":
Set MyVar = new Collection
Select Case True
Case TypeOf MyVar is Range
Debug.Print "Range"
Case TypeOf MyVar is Collection
Debug.Print "Collection"
Case Else
Debug.Print "Other cases"
End Select
You can further find out about a type using IsObject and TypeName functions:
Debug.Print IsObject(Selection) 'True
Debug.Print IsObject("Hello") 'False
Debug.Print TypeName("Hello") 'String
Debug.Print TypeName(4) 'Integer
Debug.Print TypeName(3.5) 'Double
Debug.Print TypeName(Selection) 'Range
Links:
- If...Then...Else Statement at Visual Basic for Applications Reference, msdn.microsoft.com
- TypeName Function at Visual Basic for Applications Reference, msdn.microsoft.com
- IsObject Function at Visual Basic for Applications Reference, msdn.microsoft.com
- IsArray Function at Visual Basic for Applications Reference, msdn.microsoft.com
- IsDate Function at Visual Basic for Applications Reference, msdn.microsoft.com
- IsNumeric Function at Visual Basic for Applications Reference, msdn.microsoft.com
- IsNull Function at Visual Basic for Applications Reference, msdn.microsoft.com
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