When you examine a program that is intended to solve a real problem
in the real world, a surprisingly large portion of the program will be
written just to take care of possible errors. Even in the simple web
browser from the example earlier in this tutorial, which hardly
qualifies as a real-world program, we had to handle no less than three
An incorrect number of command-line arguments to the program.
The user didn't write a web address, and just pressed the return
The browser couldn't download the web page from the given
Error handling usually consists of two parts:
detecting the error, and handling it.