C++的多态性例题展示

#include
using namespace std;
class shape
{
public:
	virtual double area() = 0;
};
class  Circle :public shape
{
public:
	Circle(float rr) :r(rr) {}
	virtual double area() { return 3.14 * r * r; }
private:
	float r;
};
class  Rectangle :public shape
{
public:
	Rectangle(float aa, float bb) :a(aa), b(bb) {}
	virtual double area() { return a * b; }

private:
	float a, b;

};
class  Trangle :public shape
{
public:
	Trangle(float dd, float gg) :d(dd), g(gg) {}
	virtual double area() { return d * g*0.5; }
private:
	float d, g;
};
void printArea(shape &s)
{
	cout << "所得的面积为"< 
纯虚函数。
 
virtual double area() = 0;表明这个返回值为0，没有什么含义，将所有的纯虚函数放在一起就是抽象类。