#include <iostream>
using namespace std;
class Shape
{
public:
    //普通函數(shù)前加virtual，普通函數(shù)變成了虛函數(shù)
　　// =0表示抽象虛函數(shù)，子類必須實(shí)現(xiàn)該函數(shù)
    virtual void printarea()=0;
    void hello(){cout<<"Shape hello function"<<endl;};
};
class Circle:public Shape
{
public:
    Circle(int a):r(a){}
    void hello(){cout<<"Circle hello function"<<endl;};
    void printarea(){cout<<"圓形面積為："<<r*r*3.14<<endl;}
private:
    int r;
};
class Rectangle:public Shape
{
public:
    Rectangle(int a,int b):x(a),y(b){}
    void hello(){cout<<"Rectangle hello function"<<endl;};
    void printarea(){cout<<"矩形面積為："<<x*y<<endl;}
private:
    int x;
    int y;
};
class Square:public Shape
{
public:
    Square(int a):l(a){}
    void hello(){cout<<"Square hello function"<<endl;};

    void printarea(){cout<<"正方形面積為："<<l*l<<endl;}
private:
    int l;
};

void prints(Shape *s) {
　　//基類指針s指向子類對(duì)象
   //s調(diào)用的函數(shù)printarea是虛函數(shù)，所以會(huì)調(diào)用子類實(shí)例的printarea
    s->printarea();
   //s調(diào)用的函數(shù)hello不是虛函數(shù)，所以只會(huì)調(diào)用基類的hello
    s->hello();
}

int main()
{
    Circle a(1);
    prints(&a);
    Square b(2);
    prints(&b);
    Rectangle c(1,2);
    prints(&c);
    return 0;
}

圓形面積為：3.14
Shape hello function
正方形面積為：4
Shape hello function
矩形面積為：2
Shape hello function