Updated: October 2009
Declares the name, arguments, and code that form the body of a Sub procedure.
Declaring and Calling Sub Procedures
You call a Sub procedure by using the procedure name followed by the argument list.
Like a Function procedure, a Sub procedure is a separate procedure that can take arguments, perform a series of statements, and change the value of its arguments. Unlike a Function procedure, a Sub procedure does not return a value, so it cannot be used in an expression.
If not explicitly specified using either Public or Private, Sub procedures are public by default, that is, they are visible to all other procedures in your script.
You cannot define a Sub procedure inside any other procedure (e.g. Function or Property Get).
In a Sub declaration, each parameter can be specified as ByRef or ByVal. If neither is specified, the default is ByRef. If ByVal is specified, the corresponding argument is always passed by value when the subroutine is called. If ByRef (or neither) is specified, the argument can be passed by reference or by value when the subroutine is called. For more information, see ByRef and ByVal Parameters.
Sub procedures can be recursive, that is, they can call themselves to perform a given task. However, recursion can lead to stack overflow.
Local Variables in Sub Procedures
The values of local variables in a Sub procedure are not preserved between calls to the procedure.
Variables that are explicitly declared in a procedure (using Dim or the equivalent) are always local to the procedure. Variables that are used but not explicitly declared in a procedure are also local, unless they are explicitly declared at some higher level outside the procedure.
If variables are not explicitly declared in a procedure, a naming conflict can occur if anything you have defined at the script level has a duplicate name. If your procedure refers to an undeclared variable that has the same name as another procedure, constant or variable, it is assumed that your procedure is referring to that script-level name. To avoid this kind of conflict, use an Option Explicit Statement to force explicit declaration of variables.
Exit Sub Statement
The Exit Sub statement causes an immediate exit from a Sub procedure. Program execution continues with the statement that follows the statement that called the Sub procedure. Any number of Exit Sub statements can appear anywhere in a Sub procedure.
The following example illustrates the use of the Sub statement.
ShowSum 5, 6 Sub ShowSum(value1, value2) Dim sum ' Determine and display the sum. sum = value1 + value2 MsgBox "The sum is: " & sum End Sub