CSE2050 Exam #3 Fall 2004, open book, open notes.  Name __________________

1. Given class Rectangle, derive class Square with a constructor
taking one parameter which is both the width and height (20 pts).

  class Rectangle: public Shape {
  private:
    int width, height;
  public:
    Rectangle(int w, int h): width(w), height(h) {}
    virtual int area() const {return width*height;}
  };

  // ANSWER
  class Square: public Rectangle {
  public:
    Square(int side): Rectangle(side, side) {}
  };


2. Write Shape as an ABSTRACT base class (20 pts).

  // ANSWER
  class Shape {
  public:
    virtual int area() const = 0;
    virtual ~Shape() {}
  };


3. Which of the following statements are legal (assuming all previous
statements are legal)?  Circle OK or ERROR  (3 pts each)

  ANSWERS                                           Comments
  --------                                          --------
     ERROR  Shape sh;                               Abstract
     ERROR  Rectangle rec;                          Constructor requires arguments
  OK        rec.area();
  OK        Square sq(5);
     ERROR  Square *sp = &rec;                      No derived pointer to base class
  OK        Rectangle *rp = sp;                     OK: base pointer to derived object
  OK        rec = sq;                               OK: derived to base conversion
     ERROR  sq = rec;                               No base to derived conversion
  OK        const Square *csp = sp;                 OK: const pointer to non-const object
  OK        sp->area();
  OK        csp->area();                            OK: area() is const
  OK        const Shape *shp = new Square(*sp);
  OK        shp->area();
     ERROR  rec == sq;                              Operator == not defined
  OK        Rectangle r(sq);                        OK: derived to base copy
  OK        Rectangle f(Square s) {return s;}       OK: derived to base return
     ERROR  f(rec);                                 No base to derived conversion
     ERROR  f(new Square);                          Type mismatch: new returns a pointer
  OK        int g(const Shape& s) {return s.area();}
  OK        g(rec);