用面向对象的方法进行设计

编写一个与图形相关的应用程序，需要处理大量图形（Shape）的信息。图形有矩形（Rectangle），圆形（Circle）和正方形（Square），应用需要计算这些图形的面积并且可能在设备上进行显示。

#include <map>
#include <queue>
#include <stack>
#include <cmath>
#include <cstdio>
#include <cstring>
#include <iostream>
#include <algorithm>


using namespace std ;


#define PI 3.14159


class Shape
{     //抽象类
public:
    Shape(){}
    ~Shape(){}
    virtual void Draw() = 0 ; //纯虚函数
    virtual double Area() = 0 ; //纯虚函数
} ;


//长方形类
class Rectangle : public Shape
{
private:
    int a;
    int b;
public:
    Rectangle():a(0),b(0){}
    Rectangle(int x,int y):a(x),b(y){}
    virtual void Draw()
    {
        cout<<"Retangle , Area = "<<Area()<<endl;
    }
    virtual double Area()
    {
        return a*b ;
    }
} ;


//圆形类
class Circle : public Shape
{
private:
    double r;
public:
    Circle(double x):r(x){}
    virtual void Draw()
    {
        cout<<"Circle , Area = "<<Area()<<endl;
    }
    virtual double Area()
    {
        return r*r*PI;
    }
} ;


//正方形类,继承Rectangle类
class Square : public Rectangle
{
private:
    int a ;
public:
    Square(int x):a(x){}
    virtual void Draw()
    {
        cout<<"Square , Area = "<<Area()<<endl;
    }
    virtual double Area()
    {
        return a*a;
    }
} ;


int main()
{
    Rectangle rect(10,20);
    Square square(10);
    Circle circle(8);


    Shape *p ;  //基类(抽象类)指针
    p = &rect ;
    cout<<p->Area()<<endl;
    p->Draw();


    p = &square ;
    cout<<p->Area()<<endl;
    p->Draw();


    p = &circle ;
    cout<<p->Area()<<endl;
    p->Draw();


    return 0 ;
}