Computer Programming Concepts and Visual Basic David I. Schneider

84 Computer Programming Concepts and Visual Basic
default value 0, and string variables default to the empty string.) The variables in a Sub procedure
are said to be local to the Sub procedure in which they reside.
EXAMPLE 4
The following program illustrates the fact that each time a Sub procedure is called, its variables are set to
their default values; that is, numerical variables are set to 0 and string variables are set to the empty string.
Private Sub cmdDisplay_Click()
‘Demonstrate that variables in a Sub procedure do
‘not retain their values in subsequent calls
picResults.Cls
Call Three
Call Three
End Sub
Private Sub Three()
Dim num As Single
‘Display the value of num and assign it the value 3
picResults.Print num;
num = 3
End Sub
[Run, and then click the command button. The following is displayed in the picture box.]
0 0
EXAMPLE 5
The following program illustrates the fact that variables are local to the part of the program in which they
reside. The variable x in the event procedure and the variable x in the Sub procedure are treated as different
variables. Visual Basic handles them as if their names were separate, such as xcmdDisplay_Click and
xTrivial. Also, each time the Sub procedure is called, the value of variable x inside the Sub procedure is
reset to 0.
Private Sub cmdDisplay_Click()
Dim x As Single
‘Demonstrate the local nature of variables
picResults.Cls
x = 2
picResults.Print x;
Call Trivial
picResults.Print x;
Call Trivial
picResults.Print x;
End Sub
Private Sub Trivial()
Dim x As Single
‘Do something trivial
picResults.Print x;
x = 3
picResults.Print x;
End Sub
[Run and then click the command button. The following is displayed in the picture box.]
2 0 3 2 0 3 2