C++ 第五章：继承和虚函数(2)

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// C++ 第五章：继承和虚函数(2)
// 2.虚函数的定义和使用

// 以纯虚函数为例
// 纯虚函数
// virtual 返回类型 函数名(参数表)=0;
#include<iostream>
using namespace std;
#define PI 3.1415

class Shape
{
public:
	virtual float Area() = 0;
};

class Rect :public Shape
{
private:
	float left;
	float top;
	float width;
	float height;
public:
	Rect()
	{
		left = 0;
		top = 0;
		width = 0;
		height = 0;
	}

	Rect(float x, float y, float w, float h)
	{
		left = x;
		top = y;
		width = w;
		height = h;
	}

	float Area()
	{
		return width*height;
	}
};

class Circle :public Shape
{
	float xCenter, yCenter, radius;
public:
	Circle()
	{
		xCenter = 0;
		yCenter = 0;
		radius = 0;
	}

	Circle(float x, float y, float r)
	{
		xCenter = x;
		yCenter = y;
		radius = r;
	}

	float Area()
	{
		return PI*radius*radius;
	}
};

int main(void)
{
	Shape *p;
	Rect R1(2, 1, 3.3, 2.0);
	// 指向子类对象的指针
	p = &R1;
	cout << "矩形面积：" << p->Area() << endl;

	// 指向子类对象的引用
	Shape &r = R1;
	cout << "矩形面积：" << r.Area() << endl;

	// 指向子类对象的指针
	p = new Circle(0, 0, 2.0);
	cout << "圆形面积：" << p->Area() << endl;

	return 0;
}