Deciding What Type of Variable to Define (Visual Basic)
When you define a variable, you must decide the following characteristics:
Its data type — what kind of data it should hold
Its lifetime — how long it should continue to exist
Its scope — what code should be able to refer to it without qualifying its name
Its access level — what code should have permission to read and write to it
Data Type
In the Dim Statement (Visual Basic) that declares the variable, include an As clause specifying the appropriate data type (such as Integer or String). The following pages can help you choose a variable's data type.
How to: Hold the Largest Possible Number in a Variable (Visual Basic)
How to: Optimize Storage of Positive Integers With Unsigned Types (Visual Basic)
How to: Hold the Most Significant Digits in a Variable (Visual Basic)
How to: Hold True and False Values in a Variable (Visual Basic)
How to: Hold Date and Time Values in a Variable (Visual Basic)
How to: Hold Data of Unknown Type in a Variable (Visual Basic)
For more information, see Data Type Summary (Visual Basic).
Lifetime
The important decision in lifetime is whether it is acceptable for the variable to cease to exist when the module, class, or procedure that declares it ceases to exist.
If the variable does not need to continue existing beyond the lifetime of its containing element, you do not need to do anything else. If the variable needs to continue to exist longer than its containing element, you can include the Static or Shared keyword in its Dim statement. For more information, see Lifetime in Visual Basic.
Scope
A variable's scope is normally the same as its declaration space, that is, the containing element in which it is declared. You must decide how extensive the variable's scope should be.
Be sure the Dim statement appears at the appropriate level, such as block, procedure, or module level. Follow the steps described in How to: Control the Scope of a Variable (Visual Basic).
For more information, see Scope in Visual Basic.
Access Level
Every variable has a default access level that depends where it is declared, that is, in what type of containing element.
If you need to specify an access level other than the default, you can include an access modifier (such as Protected or Private) in its Dim statement. You can do this only for member variables (namely, variables declared outside a procedure). Follow the steps described in How to: Control the Availability of a Variable (Visual Basic).
For more information, see Access Levels in Visual Basic.
See Also
Tasks
How to: Control the Scope of a Variable (Visual Basic)
Reference
Concepts
Variable Declaration in Visual Basic