6.17-纯虚函数.cpp

Visual C++的课件

//Implementing pure virtual functions

#include <iostream.h>

class Shape
{
public:
	Shape(){}
	virtual ~Shape(){}
	virtual long GetArea() = 0; // error
	virtual long GetPerim()= 0;
	virtual void Draw() = 0;
private:
};

void Shape::Draw()
{
	cout << "Abstract drawing mechanism!\n";
}

class Circle : public Shape
{
public:
	Circle(int radius):itsRadius(radius){}
	virtual ~Circle(){}
	long GetArea() { return 3 * itsRadius * itsRadius; }
	long GetPerim() { return 9 * itsRadius; }
	void Draw();
private:
	int itsRadius;
	int itsCircumference;
};

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


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


class Square : public Rectangle
{
public:
	Square(int len);
	Square(int len, int width);
	virtual ~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 (1)
	{
		cout << "(1)Circle (2)Rectangle (3)Square (0)Quit: ";
		cin >> choice;

		switch (choice)
		{
		case 1: sp = new Circle(5);
				break;
		case 2: sp = new Rectangle(4,6);
				break;
		case 3: sp = new Square (5);
				break;
		default: fQuit = true;
				break;
		}
		if (fQuit)
			break;

		sp->Draw();
		delete sp;
		cout << "\n";
	}
	return 0;
}