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.

Built in TypesEdit

The built in types are:

Byte
8 bit, unsigned
Integer
16 bit, signed
Long
32 bit signed
Single
32 bit floating point, range about \pm 10^{38}
Double
64 bit IEEE floating point, range about \pm 10^{308}
Currency
exact representation of decimal numbers of up to four decimal places
String
dynamically allocated UniCode strings, theorectical capacity about 2^{9} characters.
Collection
an associative array of Variants.
Date
8 byte date/time value range January 1, 100 to December 31, 9999
Object
a holder for any type of Object.
Variant
a holder for any type of value or object.

Byte, Integer & LongEdit

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 255
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 & DoubleEdit

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

StringEdit

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.

StructureEdit

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:

EnumeratationEdit

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:

Type TestEdit

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:

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Last modified on 1 September 2013, at 08:53