C++純虛數的使用

#include<iostream>
#include<string>
using namespace std;

const double PI = 3.14;

class Shape {
public:
	virtual double area()const = 0;
};

class Circle :public Shape {
public:
	double area()const { cout << "Shape:" << PI * R*R << endl;return PI * R*R; }
	Circle(int R);
private:
	int R;
};

Circle::Circle(int R)
{
	this->R = R;
}

class Rectangle:public Shape {
public:
	Rectangle(int L, int W);
	double area() const{ cout << "Rectangel:" << L * W << endl;return L * W; }
private:
	int L, W;
};

Rectangle::Rectangle(int L, int W)
{
	this->L = L;
	this->W = W;
}

int main()
{
	Circle C(10);
	Rectangle R(10, 10);
	Shape*Ptr = &C;
	Ptr->area();
	Ptr = &R;
	Ptr->area();
	system("pause");
}