Programming Excel with VBA and .NET

Scope and Lifetime

Dim is not the only way to declare a variable. The full list of declaration keywords is shown in Table 2-6.

Table 2-6. Visual Basic declaration statements

Statement	Use to declare	Available
Dim	A variable with the default scope	Inside or outside a procedure
Public	A variable or procedure that is available from other modules or classes	Outside a procedure only
Private	A variable or procedure that is not available from other modules or classes	Outside a procedure only
Static	A variable that retains its value between procedure calls	Inside a procedure only

Which statement you use to declare a variable and where you declare it determines the scope and lifetime of that variable. Scope is the range of places from which a name is visible. Dim, Public, and Private are statements that specify scope. Lifetime is how long Visual Basic retains the value of a variable; Static specifies lifetime.

There are three levels of scope in a Visual Basic project:

• Local variables are declared with Dim inside a procedure and are visible only from within that procedure.

• Module-level variables are declared outside of a procedure with Dim or Private and are visible only from all procedures within that module or class.

• Global variables are declared outside of a procedure with Public and are visible from all procedures in all modules and classes within the project.

Figure 2-10 illustrates the different levels of scope within a Visual Basic project.

Tip

It’s a common practice ...