Programming:Visual Basic Classic/Data Types

Introduction

Datatypes in Visual Basic can be divided into three groups:

native

those 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

these are the basis for object oriented programming in Visual Basic. Note that forms and the various Add-inn and database designers are also classes.

Built in Types

The built in types are:

Byte

eight bit, unsigned

Integer

16 bit, signed

Long

32 bit signed

Single

32 bit floating point, range about

Double

64 bit IEEE floating point, range about

Currency

exact representation of decimal numbers of up to four decimal places (is this correct)

String

dynamically allocated UniCode strings, theorectical capacity about 2⁹ characters.

Collection

an associative array of Variants.

Object

a holder for any type of Object.

Variant

a holder for any type of value or object.

Byte, Integer & Long

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.

Some functions you need to know: Int()

Int() converts a decimal value into a integer value:

 Dim i as Integer
 i=Int(3.9)
 Print i

Will print:

 3

Single & Double

These data types can store decimal values. "Double" compared to "Single" is similar to the "Long" compared to "Integer":

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

Will print:

      3.14

String

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:

      Print "Wiki" & "book" & "s"

Will print:

      Wikibooks

A normal string variable occupies 10 bytes plus its own size(the string's size) of RAM and can hold as long as 0 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 new line(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 convertable).

      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

If you don't do the conversion. You'll end up getting Type Mismatch Errors.