Page 93 - Open Soource Technologies 304.indd

Unit 4: VB Programming Fundamentals

Dim is shorthand for dimension and is a rather archaic expression that instructs Visual Basic to
allocate enough memory to contain the variable that follows the Dim keyword. Therefore, Dim
i As Integer allocates less memory (2 bytes) than Dim s As Double (8 bytes). There is no way
to make a variable declared within a procedure visible outside of that procedure.

The public keyword is used to make a variable visible throughout an application. Public can be
used only at the module level and cannot be used within a procedure. Usually, the Public
keyword is used only in standard modules that are not part of a form. Every variable declared
in the general section of the standard module is public throughout the application unless the
Private keyword is used. Private restricts the visibility of a variable to the module in which the
variable is declared.

4.3.10 Local Variables
A local variable is one that is declared inside a procedure. This variable is only available to the
code inside the procedure and can be declared using the Dim statements as given below.
Dim sum As Integer
The local variables exist as long as the procedure in which they are declared, is executing. Once
a procedure is executed, the values of its local variables are lost and the memory used by these
variables is freed and can be reclaimed. Variables that are declared with keyword Dim exist only
as long as the procedure is being executed.

4.3.11 Static Variables
Static variables are not reinitialized each time Visual Invokes a procedure and therefore retains
or preserves value even when a procedure ends. In case we need to keep track of the number
of times a command button in an application is clicked, a static counter variable has to be
declared. These static variables are also ideal for making controls alternately visible or invisible.
A static variable is declared as given below:

Static intPermanent As Integer
Variables have a lifetime in addition to scope. The values in a module-level and public variables
are preserved for the lifetime of an application whereas local variables declared with Dim exist
only while the procedure in which they are declared is still being executed. The value of a local
variable can be preserved using the Static keyword. The follwoing procedure calculates the
running total by adding new values to the previous values stored in the static variable value.
Function RunningTotal ( )
Static Accumulate
Accumulate = Accumulate + num
RunningTotal = Accumulate
End Function

If the variable Accumulate was declared with Dim instead of static, the previously accumulated
values would not be preserved accross calls to the procedure, and the procedure would return
the same value with which it was called. To make all variables in a procedure static, the Static
keyword is placed at the beginning of the procedure heading as given in the below statement.

Static Function RunningTotal ( )

LOVELY PROFESSIONAL UNIVERSITY 87