Laboratory II: Graphics System

Note:  This machine problem needs an understanding of inheritance and polymorphism. For a clearer problem definition please refer to page 659 of the book given by Mr. Sy in our Facebook group.
Deadline: Thursday, July, 14, 2011. NO EXTENSION. NO WORK IN THE LAB, NO SCORE (0).

1. Consider a graphics system that has classes for various figures, say rectangles, squares, triangles, circles, and so on. For example, a rectangle might have data members height, width, and center point, while a square and circle might have only a center point and an edge length or radius, respectively. In a well-designed system these would be derived from a common class, Figure. You are to implement such a system. The class Figure is the base class. You should add only Rectangle and Triangle classes derived from Figure. Each class has stubs for member functions erase and draw. Each of these member functions outputs a message telling what function has been called and what the class of the calling object is. Since these are just stubs, they do nothing more than output this message. The member function center calls erase and draw to erase and redraw the figure at the center. Because you have only stubs for erase and draw, center will not do any “centering” but will call the member functions erase and draw. Also, add an output message in the member function center that announces that center is being called. The member functions should take no arguments. There are three parts to this project:
a. Do the class definitions using no virtual functions. Compile and test.
b. Make the base class member functions virtual. Compile and test.
c. Explain the difference in results.
For a real example, you would have to replace the definition of each of these member functions with code to do the actual drawing. You will be asked to do this in Programming Project 2.
Use the following main function for all testing:
//This program tests Programming Problem 1.
#include <iostream>
#include "figure.h"
#include "rectangle.h"
#include "triangle.h"
using std::cout;
int main( )
{
    Triangle tri;
    tri.draw( );
    cout <<
      "\nDerived class Triangle object calling center( ).\n";
    tri.center( ); //Calls draw and center
    Rectangle rect;
    rect.draw( );
    cout <<
      "\nDerived class Rectangle object calling center().\n";
    rect.center( ); //Calls draw and center
    return 0;
}
2. Flesh out Programming Problem 1. Give new definitions for the various constructors and
member functions Figure::center, Figure::draw, Figure::erase, Triangle::draw, Triangle::erase, Rectangle::draw and Rectangle::erase so that the draw functions actually draw figures on the screen by placing the character ’*’ at suitable locations on the screen. For the erase functions, you can simply clear the screen (by outputting
blank lines or by doing something more sophisticated). There are a lot of details in this and
you will have to decide on some of them on your own.