C++ tutorial: functions

Functions are the basic organizing unit in C programs
No practical C/C++ program is simple enough for its entire operation to be contained within the 'main' function, as the previous examples have been. It is now time properly to introduce the idea of functions: the basic unit of organization in C programs. In C++, a higher-level unit of organization is introduced: the class. This does not mean that functions are unimportant: quite the opposite is the case.

So what is a function? It is simply a self-contained piece of program with certain inputs and outputs. When a function is activated it is said to be called. Functions can call other functions, so in effect a complex job can broken into progressively smaller, simpler ones. This principle is called stepwise refinement.

If you have been following the example used so far, you may have noticed functions being introduced without much comment. For example, in welcome2.cpp, a trivial procedure was divided into two even more trivial functions. Before starting a description of how to define more useful functions, we will have a look at some of the built-in functions provided in the 'standard library'.