Microsoft® Small Basic
Debugging Aids
Estimated time to complete this lesson: 1 hour
Debugging Aids
In this lesson, you will learn how to:
Use the TextWindow.WriteLine operation to
debug your programs.
Debugging
Debugging is how you detect and resolve any defects in your computer program.
Every programmer develops the skill to detect bugs and debug his or her
program.
Even a minor bug in a program can defeat the
efforts of the programmer!
While working on large programs, programmers
write debugging support code that is not included
in the final program. This code helps determine the
point at which a program fails to run.
TextWindow.WriteLine As a Debugging Helper
So how can you debug programs in Small Basic?
To debug your program, you can use the
TextWindow.WriteLine operation. This operation
acts as a debugging helper, and it provides
information to help debug your program.
TextWindow.WriteLine As a Debugging Helper
Let’s look at an example that
uses the TextWindow.WriteLine
operation for debugging.
In this program, you first display
an ellipse in the graphics window.
If your program does not run as
expected, you must debug it!
You can use the
TextWindow.WriteLine operation
as a debugger at this point. This
operation can help you trace the
value of “i” on every iteration of
the For…EndFor loop. The value
of “i” appears in a separate text
window so that you can easily
detect a bug and fix it.
TextWindow.WriteLine As a Debugging Helper
Now, let’s use the TextWindow.WriteLine
operation in another program and see how it
can help you debug the program.
In this example, you use the Flickr
object to download a photo from
www.flickr.com and display it on
the graphics window.
The image that you requested does not appear in
the graphics window. It’s time to debug your code!
TextWindow.WriteLine As a Debugging Helper
You might not be connected to the
Internet, or you might not have access
to the website.
As you can see, the text window is not displaying
the path of the image, which means that you are
not connected to the Internet.
To check this possibility,
you can use the
TextWindow.WriteLine
operation to display the
path of the image from
the website. If the
Internet connection is
working correctly, the
path of the image will
appear in the text
window. Otherwise, the
text window will not
display any path.
TextWindow.WriteLine As a Debugging Helper
Now, let’s write a program to copy a file and display
its contents in the text window.
In this example, if the
CopyFile operation is
successful, the text window
displays the contents of the
file.
You may not see the contents of the
file in the text window because:
• The specified source or destination
may be incorrect.
• The file may not exist at the specified
source.
• The name of the specified file may be
incorrect.
Now how do we detect the error? It’s
time to debug your code again…
TextWindow.WriteLine As a Debugging Helper
Let’s use the TextWindow.WriteLine
operation to detect the error.
You can modify your
program and use
TextWindow.WriteLine to
display the return value of
the CopyFile operation in the
text window. The return
value will be either SUCCESS
or FAILED.
So, if your program cannot
run because of the CopyFile
operation error, you
immediately know about it!
Let’s Summarize…
Congratulations! Now you know how to:
Use the TextWindow.WriteLine operation to debug
programs.
Show What You Know
A program creates a slide show of images in
the graphics window. All these images are
stored in a local folder. With every mouse click,
a different image appears in the graphics
window.
Use the TextWindow.WriteLine operation as a
debugging helper by displaying the path of
each image in the text window.