项目三（oj）。立体类族共有的抽象类

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程序：
//编写一个程序，定义抽象基类Shape，由它派生出5个派生类：// Circle(圆形)、Square(正方形)、Rectangle(矩形)、Trapezoid(梯形)、Triangle(三角形)。//用虚函数分别计算几种图形面积，并求它们之和。//要求用基类指针数组，使它每一个元素指向一个派生类对象#include <iostream>#include <iomanip>#define pi 3.1415926using namespace std;class Shape{public:    virtual double area()= 0;//抽象类};class Circle:public Shape//圆形{private:    double radius;public:    Circle(double r):radius(r){}    double area()    {        return pi*radius*radius;    }};class Rectangle:public Shape//矩形{private:    double length,width;public:    Rectangle(double l,double w):length(l),width(w){}    double area()    {        return length*width;    }};class Trapezoid:public Shape//梯形{private:    double hlength,llength,hight;public:    Trapezoid(double hl,double l,double h):hlength(hl),llength(l),hight(h){}    double area()    {        return (hlength+llength)*hight/2;    }};class Square:public Shape//正方形{private:    double length;public:    Square(double l):length(l){}    double area()    {        return length*length;    }};class Triangle:public Shape//三角形{private:    double length,hight;public:    Triangle(double l,double h):length(l),hight(h){}     double area()    {        return (length*hight)/2;    }};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;}
结果：
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