Computer Programming Concepts and Visual Basic David I. Schneider

■ FORM-LEVEL VARIABLES
Visual Basic provides a way to make a variable visible to every procedure in a form’s code without
being passed. Such a variable is called a form-level variable. Form-level variables appear
at the top of the code window and are separated from the rest of the code by a horizontal separator
line. Inside the code window, you can move to them either by pressing Ctrl+Home or
clicking on General in the Object list box. Form-level variables are said to reside in the
(Declarations) section of (General) and are declared with the following steps.
1. Invoke a code window if one is not already active.
2. Click on the down-arrow to the right of the Object list box.
3. Click on (General).
4. Click on (Declarations) in the Procedure list box.
5. Type in a declaration statement, such as Dim strVar As String, and press the
Enter key.
When a form-level variable is assigned a value by a procedure, it retains that value when
the procedure is exited. In this text, we rarely use form-level variables until Section 6.
EXAMPLE 6
The following program contains the form-level variables num1 and num2. Their Dim statement does not
appear inside a procedure.
Dim num1 As Single, num2 As Single ‘In (Declarations) section of (General)
Private Sub cmdDisplay_Click()
‘Display the sum of two numbers
num1 = 2
num2 = 3
picResults.Cls
Call AddAndIncrement
picResults.Print
picResults.Print “num1 = “; num1
picResults.Print “num2 = “; num2
End Sub
Private Sub AddAndIncrement()
‘Display numbers and their sum
picResults.Print “The sum of”; num1; “and”; num2; “is”; num1 + num2
num1 = num1 + 1
num2 = num2 + 1
End Sub
[Run, and click the command button. The following is displayed in the picture box.]
The sum of 2 and 3 is 5
num1 = 3
num2 = 4
Sub Procedures, Part II 85
In the preceding example, we had to click a command button to assign values to the
form-level variables. In some situations, we want to assign a value immediately to a formlevel
variable, without requiring the user to perform some specific action. Visual Basic has
a special event procedure called Form_Load that is automatically activated as soon as the
program is run, even before the form is created. The Form_Load template is invoked by double-clicking
on the form itself.