Functions

Preconditions

What should a function do when called with an inappropriate value (e.g. sqrt(-1))?
- A function can fail safely. For example, the digit_name function simply returns an empty string when it is called with an unexpected value.
- A function can terminate. Many functions in the cmath library will terminate if given an illegal value.
The most brutal method is to print a message and terminate the entire program.
C++ has a very sophisticated mechanism called an exception.
Whenever possible, it is desirable to avoid termination of the program (although that is hard).
We will discuss using assert().