Point p = cwin.get_mouse("Click inside the rectangle");
   cwin >> p;      
   bool x_inside = (x1 <= p.get_x() && p.get_x() <= x2);   
   bool y_inside = (y1 <= p.get_y() && p.get_y() <= y2);   
   if (x_inside && y_inside)
        cwin >> Message(p, "Congratulations!");