THAT FAIL are much too common.
Programs are fragile.
A tiny error can cause a program to misbehave or crash. Most of us are familiar with this from our own experience with computers. And we've all heard stories about software glitches that cause spacecraft to crash, telephone service to fail, and, in a few cases, people to die. Programs don't have to be as bad as they are. This chapter will look at issues of correctness and robustness of programs.