Computer Programming Concepts and Visual Basic David I. Schneider

can then alter the expression in the Expression text box and select one of the three Watch
types. To delete an expression from the Watch window, right-click on the expression and then
click on “Delete Watch.” To alter an expression in the Watch window, right-click on the
expression and click on “Edit Watch.”
THE LOCALS WINDOW
The Locals window, invoked by clicking on “Locals Window” in the View menu, is a
feature that was new to Visual Basic in version 5.0. This window automatically displays the
names, values, and types of all variables in the current procedure. See Figure D.3. You can
alter the values of variables at any time. In addition, you can examine and change properties
of controls through the Locals window.
FIGURE D.3 The Locals Window
STEPPING THROUGH A PROGRAM
The program can be executed one statement at a time, with each press of an appropriate function
key executing a statement. This process is called stepping (or stepping into). After each
step, values of variables, expressions, and conditions can be displayed from the debugging
windows, and the values of variables can be changed.
When a procedure is called, the lines of the procedure can be executed one at a time,
referred to as “stepping through the procedure,” or the entire procedure can be executed at
once, referred to as “stepping over a procedure.” A step over a procedure is called a procedure
step. In addition, you can execute the remainder of the current procedure at once,
referred to as “stepping out of the procedure.”
Stepping begins with the first line of the first event procedure invoked by the user. Program
execution normally proceeds in order through the statements in the event procedure.
However, at any time the programmer can specify the next statement to be executed.
As another debugging tool, Visual Basic allows the programmer to specify certain lines
as breakpoints. Then, when the program is run, execution will stop at the first breakpoint
reached. The programmer can then either step through the program or continue execution to
the next breakpoint.
The tasks discussed previously are summarized below, along with a means to carry out
each task. The tasks invoked with function keys can also be produced from the menu bar.
Step Into: Press F8
Step Over: Press Shift+F8
Step Out: Press Ctrl+Shift+F8
Set a breakpoint: Move cursor to line, press F9
Remove a breakpoint: Move cursor to line containing
breakpoint, press F9
Clear all breakpoints: Press Ctrl+Shift+F9
Set next statement: Press Ctrl+F9
Continue execution to next breakpoint
or the end of the program: Press F5
Run to cursor: Press Ctrl+F8
Appendix D 459