programming-for-dummies

98
Fixing a Program with a Debugger
your program that caused that problem. Then you can fix the problem, as
shown in Figure 4-5.
Sometimes when programmers find one error and fix it, their fix accidentally
creates another error in the program.
Here are the two types of debuggers:
✦ Source-level: Lets you examine your source code line by line. So if you
write a program in BASIC, a source-level debugger shows you each line
of your entire BASIC program.
✦ Machine-language: Lets you examine the machine language code, line
by line, that your compiler created from your source code. Programmers
often use machine-language debuggers to examine programs when they
don’t have access to the source code, such as a computer virus or a
rival’s program.
Stepping line by line through a small program may be feasible, but in a large
program that consists of a million lines of code, stepping line by line would
take far too long. So to make stepping easier, most debuggers include breakpoints
and stepping over/stepping out commands.
Figure 4-5:
Stepping
through a
program,
line by line,
can help
you find
errors or
bugs in your
program.
Breakpoints
A breakpoint lets you skip over the parts of your program that you already
know work. So if you have a program that’s 10,000 lines long and you know
the problem is somewhere in the last 1,000 lines of code, there’s no point
stepping through those first 9,000 lines of code.