19. More access control examples

• Member access includes members of other objects of our class:

  
  // point.h
  class Point
  {
  private:
      int m_x;
      int m_y;
      void reset_coord();
  public:
      double distance_to_origin();
      double distance_to_point();
  };
  
  // point.cpp
  double Point::distance_to_point( Point other )
  {
      // Access to private members m_x, m_y is allowed,
      // because we are in a member function:
      double x_diff = m_x - other.m_x;
      double y_diff = m_y - other.m_y;
      return sqrt( x_diff * x_diff + y_diff * y_diff );
  }