Variables, Constant and Data Types

Data Types 

• Visual Basic is rich in its data types. 
• Data types are used to declare the variables. 
• At the time of declaration, memory is allocated for the variables. 
• Different data types are used to store different types of values.

Table: Memory storage for data types 

Data Type	Storage	Data Type	Storage
Byte	1 byte	String (variable-length)	Length + 10 bytes
Boolean	2 bytes	String (Fixed-Length)	Length of string
Integer	2 bytes	Currency	8 bytes
Long	4 bytes	Decimal	12 bytes
Single	4 bytes	Object	4 bytes
Double	8 bytes	Variant (numeric)	16 bytes
Date	8 bytes	Variant (text)	length +22 bytes

Table: Data types & their value range

Data Type	Value Range
Byte	0 to 255
Boolean	True/False
Integer	-32,768 to 32,767
Long	-2,147,483,648 to 2,147,483,647
Single	-3.402823*10^3 to -1.401298*10^45 for negative values 1.401298*10^-45 to 3.402823*10^38 for positive values
Double	-1.79*10^308 to -4.94*10^-324 for negative values 4.94*10^-324 to 1.79*10^308 for positive values
Date	January 1, 100 to December 31, 9999
String (Variable length)	0 to approximately 2 billion characters
String (Fixed length)	1 to 65,400 characters
Currency	-922,337,203,685,477.5808 to 922,337,203,685,477.5807
Decimal	+,-79,228,162,514,264,337,593,543,950,335 if no decimal is used      +,-7.9228162514264337593543950335 (28 decimal places)
Object	Any object
Variant (numeric)	Any value as 16px as Double
Variant (text)	Same as variable length string

EXAMPLE OF DATA TYPE :

Use Integer data Type

Dim number As Interger
number=10

Dim NIC As Long
NIC=870740913

You can use any numeric values for this data type.

Use String Data Type

Dim user_name As String
user_name="Hemantha" 

Use String Data Type

Dim national_date As Date 
national_date=1948/02/04

Use Boolean  Data Type

Dim Do_you_love_me  As Boolean 
Do_you_love_me=True 

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Variable 

• Variable is used to store value. 
• The value of the variable may vary during the program execution.

Naming Rules of variables 

• A variable name must begin with an alphabet.
• It cannot be more than 255 characters.
• The variable name must not contain any special character like %,&,!,#,@ or $.
• And finally, it has to be unique within the same scope.

Variable Declaration 

• Depending on where the variables are declared and how they are declared, there are many ways to declare a variable in visual basic. 
• When you declare a variable, memory space for the variable is reserved. 
• This is called memory allocation. 
• Different amount of memory space is reserved for different data types. 

You can declare a variable with the 'dim' keyword.

Syntax:

            Dim variable As [Type]

       

Example:

Private Sub cmdSum_Click()
    Dim m As Integer
    Dim n As Integer
    Dim sum As Integer

    m = 10     'm is a variable, 10 is a constant
    n = 30
    sum = m + n

    Print "The sum is " & sum

End Sub

Output: The sum is 40

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Constant

• Constant is a fixed value that does not change during the program execution. 
• You can define your own constant to use it in your program.

Creating your own constants

• You can create your own constant to use it in your program. 
• The value of the constant remains unchanged throughout the program.

Example:

Private Sub cmdCalculate_Click()
    Const pi = 3.1415926   'or Const pi As Double = 3.1415926
    Dim area As Double, r As Double
    r = 2
    area = pi * r * r
    Print area
End Sub

Output: 12.5663704