text: // listing 7.2 - protos.cpp -- using prototypes and function calls
  #include <iostream>
  void cheers(int); // prototype: no return value
  double cube(double x); // prototype: returns a double
  int main()
  {
     using namespace std;
     cheers(5); // function call
     cout << "Give me a number: ";
     double side;
     cin >> side;
     double volume = cube(side); // function call
     cout << "A " << side << "-foot cube has a volume of ";
     cout << volume << " cubic feet.\n";
     cheers(cube(2)); // prototype protection at work
     return 0;
  }
  
  void cheers(int n)
  {
     using namespace std;
     for (int i = 0; i < n; i++)
        cout << "Cheers! ";
     cout << endl;
  }
  
  double cube(double x)
  {
     return x * x * x;
  }
  