Computer Programming Concepts and Visual Basic David I. Schneider

460 Computer Programming Concepts and Visual Basic
SIX WALKTHROUGHS
The following walkthroughs use the debugging tools with the programming structures covered
in Sections 2, 3, 4, and 5.
STEPPING THROUGH AN ELEMENTARY PROGRAM: SECTION 2
The following walkthrough demonstrates several capabilities of the debugger.
1. Create a form with a command button (cmdButton) and a picture box (picBox).
Set the AutoRedraw property of the picture box to True. (During the debugging
process, the entire form will be covered. The True setting for AutoRedraw prevents
the contents of the picture box from being erased.)
2. Double-click on the command button and enter the following event procedure:
Private Sub cmdButton_Click()
Dim num As Single
picBox.Cls
num = Val(InputBox(“Enter a number:”))
num = num + 1
num = num + 2
picBox.Print num
End Sub
3. Press F8, click the command button, and press F8 again. A yellow arrow points
to the picBox.Cls statement and the statement is highlighted in yellow. This
indicates that the picBox.Cls statement is the next statement to be executed.
(Pressing F8 is referred to as stepping. You can also step to the next statement
of a program with the Step Into option from the Debug menu.)
4. Press F8. The picBox.Cls statement is executed and the statement involving
InputBox is designated as the next statement to be executed.
5. Press F8 to execute the statement containing InputBox. Respond to the request
by typing 5 and clicking the OK button.
6. Press F8 again to execute the statement num = num + 1.
7. Let the mouse sit over any occurrence of the word “num” for a second or so.
The current value of the variable will be displayed in a small box. See Figure
D.4.
FIGURE D.4 Obtaining the Value of a Variable
8. Click on the End icon to end the program.
9. Move the cursor to the line
num = num + 2
and then press F9. A red dot appears to the left of the line and the line is displayed
in white text on a red background. This indicates that the line is a break-