could you explain this?

Code:

---

//Listing 14.7. Shape classes.

#include <iostream>
using std::cout;
using std::cin;
using std::endl;

class Shape
{
public:
        Shape(){}
        virtual ~Shape(){}
        virtual long GetArea() { return -1; } // error
        virtual long GetPerim() { return -1; }
        virtual void Draw() {}
private:
};

class Circle : public Shape
{
public:
        Circle(int radius):itsRadius(radius){}
        ~Circle(){}
        long GetArea() { return 3 * itsRadius * itsRadius; }
        long GetPerim() { return 6 * itsRadius; }
        void Draw();
private:
        int itsRadius;
        int itsCircumference;
};

void Circle::Draw()
{
        cout << "Circle drawing routine here!\n";
}


class Rectangle : public Shape
{
public:
        Rectangle(int len, int width):
        itsLength(len), itsWidth(width){}
        virtual ~Rectangle(){}
        virtual long GetArea() { return itsLength * itsWidth; }
        virtual long GetPerim() {return 2*itsLength + 2*itsWidth; }
        virtual int GetLength() { return itsLength; }
        virtual int GetWidth() { return itsWidth; }
        virtual void Draw();
private:
        int itsWidth;
        int itsLength;
};

void Rectangle::Draw()
{
        for (int i = 0; i<itsLength; i++)
        {
                for (int j = 0; j<itsWidth; j++)
                        cout << "x ";

        cout << "\n";
        }
}

class Square : public Rectangle
{
public:
        Square(int len);
        Square(int len, int width);
        ~Square(){}
        long GetPerim() {return 4 * GetLength();}
};

Square::Square(int len):
Rectangle(len,len)
{}

Square::Square(int len, int width):
Rectangle(len,width)
{
        if (GetLength() != GetWidth())
        cout << "Error, not a square... a Rectangle??\n";
}

int main()
{
        int choice;
        bool fQuit = false;
        Shape * sp;

        while ( !fQuit )
        {
                cout << "(1)Circle (2)Rectangle (3)Square (0)Quit: ";
                cin >> choice;

                switch (choice)
                {
                case 0:        fQuit = true;
                                break;
                case 1: sp = new Circle(5);
                                break;
                case 2: sp = new Rectangle(4,6);
                                break;
                case 3: sp = new Square(5);
                                break;
                default: cout<<"Please enter a number between 0 and 3"<<endl;
                                continue;
                                break;
                }
                if( !fQuit )
                        sp->Draw();
                delete sp;
                sp = 0;
                cout << "\n";
        }
 int exit;cin>>exit;
        return 0;
}

---

I don't see the defition for the rectangle constructor.....please explain.........

never mind I see it now.....it's just a little bit different that usual (for the book)
Rectangle(int len, int width):
itsLength(len), itsWidth(width){}

I sure am glad you spotted it. It's a bit hidden.

The author didn't exactly try to hide it, it's where the constructor usually is placed (as the first public method). Of course I would have done it a different way when using an initializer list, either make the definition global and comment so that everything is nice and neat and easy to find:

Code:

---

// Constructor fleshy
Rectangle::Rectangle(int len, int width):
  itsLength(len), itsWidth(width)
{
}

---

or put it all on one line inside the class so that it's easier to read:

Code:

---

Rectangle(int len, int width): itsLength(len), itsWidth(width) {}

---

It was probably broken into two lines for space sake, but to some that would make it very difficult to follow, especially people who don't see initializer lists often.

-Prelude

Yeah I guess that's what confused me a bit, because I wasn't really used to see the constructor definition like that.