Thread: 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){}

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.