// Ex7_08.cpp
  // Creating a friend function of a class
  include <iostream>
  using std::cout;
  using std::endl;
  
  class CBox                             // Class definition at global scope
  {
    public:
  
      // Constructor definition
      CBox(double lv = 1.0, double bv = 1.0, double hv = 1.0)
      {
        cout << endl << "Constructor called.";
        m_Length = lv;                   // Set values of
        m_Width = bv;                    // data members
        m_Height = hv;
      }
  
      // Function to calculate the volume of a box
      double Volume()
      {
        return m_Length*m_Width*m_Height;
      }
  
    private:
      double m_Length;                   // Length of a box in inches
      double m_Width;                    // Width of a box in inches
      double m_Height;                   // Height of a box in inches
  
    // Friend function
    friend double BoxSurface(CBox aBox);
  };
  
  // friend function to calculate the surface area of a Box object
  double BoxSurface(CBox aBox)
  {
    return 2.0*(aBox.m_Length*aBox.m_Width +
                aBox.m_Length*aBox.m_Height +
                aBox.m_Height*aBox.m_Width);
  }
  
  int main()
  {
    CBox match(2.2, 1.1, 0.5);           // Declare match box
    CBox box2;                           // Declare box2 - no initial values
  
    cout << endl
         << "Volume of match = "
         << match.Volume();
  
    cout << endl
         << "Surface area of match = "
         << BoxSurface(match);
  
    cout << endl
         << "Volume of box2 = "
         << box2.Volume();
  
    cout << endl
         << "Surface area of box2 = "
         << BoxSurface(box2);
  
    cout << endl;
    return 0;
  }