For example, we might use a function to calculate the length of the hypotenuse of a right triangle:

cout << "Enter triangle width: ";
cin >> w;
cout << "Enter triangle height: ";
cin >> h;
cout << "The hypotenuse is " << hypotenuse(w, h) << endl;

Using functions can act as documentation (if they are given appropriate names). Compare the instant recognition of hypotenuse(w, h) to sqrt(w*w+h*h).