c++习题1_H_虚函数-计算图形面积

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/**作者：lws*完成时间：2014/6/14*描述：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。*输入：12.6 3.5 4.5 8.4 2.0 4.5 3.2 4.5 8.4*输出：total of all areas=574.11*/#include <iostream>#include <iomanip>const double PI=3.14159；using namespace std;class Shape //抽象类(包含纯虚函数的类){public:    virtual double Area()=0; //纯虚函数(没有函数体的虚函数)};//圆形类class Circle:public Shape{public:    Circle(double r):radius(r){}    double Area()    {       return PI*radius*radius;    }private:    double radius;};//正方形类class Square:public Shape{public:    Square(double s):side(s){}    double Area()    {        return side*side;    }private:    double side;};//矩形类class Rectangle:public Shape{public:    Rectangle(double l,double w):length(l),width(w){}    double Area()    {        return length*width;    }private:    double length;    double width;};//梯形类class Trapezoid:public Shape{public:    Trapezoid(double u,double d,double h):up(u),down(d),height(h){}    double Area()    {        return 1/2.0*(up+down)*height;    }private:    double up,down,height;};//三角形类class Triangle:public Shape{public:    Triangle(double a1,double b1):a(a1),b(b1){}    double Area()    {        return 1/2.0*a*b;    }private:    double a,b;};void PrintArea(Shape &p){    cout<<p.Area();//p.Aare()函数处理方法：在编译阶段，不确定调用哪一个函数，而是在此处保留5个虚函数Area()的5个入口地址。//在程序运行时，根据实参的类型来确定调用5个虚函数之一。}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);    //抽象类的指针引用——>由抽象类派生出的类的对象    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;    return 0;}
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