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Unit 4: VB Programming Fundamentals

temptation to create a global variable it is much better torefer to the text in the text box this
way (assuming the name of the dialog form you have created is Dialog):
intNumberBalloons = Dialog.TextBox1.Text

This avoids setting up a global variable needlessly. In fact, one of the most important aspects
of Visual Basic programming is variable scope. In general, you should restrict variables to the
smallest scope possible.

There are three levels of variable scope in Visual Basic, as follows:
“ Variables declared in procedures are private to the procedure.
“ Variables declared at the form or module level in the form or modules (General) section using Dim,
ReDim, Private, Static, or Type are form- or module-level variables. These variables are avail-
able throughout the module.

“ Variables declared at the module level in the modules (General) section using Public are global
and are available throughout the project, in all forms and modules. Note that you cannot use
Public in procedures.

If you use the Option Private Module statement in a module or form, all variables
in the module or form become private to the module, no matter how they are
declared.

4.3.5 Implicit and Explicit Variable Declaration
Declaring a variable tells Visual Basic to reserve space in memory. It is not must that a variable
should be declared before using it. Automatically whenever Visual Basic encounters a new
variable, it assigns the default variable type and value. This is called implicit declaration. Though
this type of declaration is easier for the user, to have more control over the variables, it is
advisable to declare them explicitly. The variables are declared with a Dim statement to name
the variable and its type. The As type clause in the Dim statement allows to define the data type
or object type of the variable. This is called explicit declaration.
Syntax
Dim variable [As Type]
For example,
Dim strName As String
Dim intCounter As Integer

4.3.6 Using Option Explicit Statement
It may be convenient to declare variables implicitly, but it can lead to errors that may not be
recognized at run time. Say, for example a variable by name intcount is used implicitly and is
assigned to a value. In the next step, this field is incremented by 1 by the following statement
Intcount = Intcount + 1
This calculation will result in intcount yielding a value of 1 as intcount would have been
initialized to zero. This is because the intcount variable has been mityped as incont in the right
hand side of the second variable. But Visual Basic does not see this as a mistake and considers
it to be new variable and therefore gives a wrong result.

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