14-2-形状类族的中的纯虚函数(OJ版)

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/** 作    者： 霍雨佳* 完成日期：2014 年5月27日* 版 本 号：v1.0* 问题描述：形状类族的中的纯虚函数* 样例输入：* 样例输出：* 项目要求：*/#include <iostream>#include <iomanip>#define pi 3.1415926using namespace std;class Shape{    public:    virtual double area()=0;};class Circle:public Shape//（圆形）{    public:    Circle(double a):r(a){}    double area()    {        return pi*r*r;    }    private:    double r;};class Square:public Shape//(正方形)、{    public:    Square(double a):j(a){}    double area()    {        return j*j;    }     private:    double j;};class Rectangle:public Shape//（矩形）{     public:    Rectangle(double a,double b):l(a),m(b){}    double area()    {        return l*m;    }     private:    double l;    double m;};class Triangle:public Shape//（三角形）{     public:     Triangle(double a,double b):y(a),n(b){}    double area()    {        return (y*n)/2;    }    private:    double y;    double n;};class Trapezoid:public Shape//(梯形)、{    public:     Trapezoid(double q,double s,double x):y(q),n(s),m(x){}    double area()    {        return ((y+n)*m)/2;    }    private:    double y;    double n;     double m;};int main(){    float r,a,b,w1,w2,w,h;    cout<<fixed<<setprecision(2);    cin>>r;    Circle circle(r);    cin>>a;    Square square(a);    cin>>a>>b;    Rectangle rectangle(a,b);    cin>>w1>>w2>>h;    Trapezoid trapezoid(w1,w1,h);    cin>>w>>h;    Triangle triangle(w,h);    Shape *pt[5]= {&circle,&square,&rectangle,&trapezoid,&triangle};    double areas=0.0;    for(int i=0; i<5; i++)        areas=areas+pt[i]->area();    cout<<"total of all areas="<<areas<<endl;    return 0;}
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