用虚函数分别计算各种图形的面积

一.问题描述：

定义抽象基类Shape，由它派生出五个派生类：Circle（圆形）、Square（正方形）、Rectangle（ 长方形）、Trapezoid （梯形）和Triangle （三角形），用虚函数分别计算各种图形的面积，并求出它们的和。要求用基类指针数组。使它的每一个元素指向一个派生类的对象。PI=3.1415926

二.代码实现：

#include<iostream>
using namespace std;
class Shape{
public:
    virtual double Area()const=0;
};
class Circle:public Shape{
public:
    Circle(double radius):r(radius){
        
    }
    double r;
    virtual double Area()const{
        return    3.1415926*r*r;
    }

};
class Square:public Shape{
public:
    Square(double side):s(side){
        
    }
    double s;
    virtual double Area()const{
        return s*s;
    }
};
class Rectangle:public Shape{
public:
    Rectangle(double a1,double b1):a(a1),b(b1){
        
    }
    double a,b;
    virtual double Area()const{
        return a*b;
    }
};
class Triangle:public Shape{
public:
    Triangle(double width,double height):w(width),h(height){
        
    }
    double w,h;
    virtual double Area()const{
        return 0.5*w*h;
    }
};
class Trapezoid:public Shape{
public:
    Trapezoid(double shangd,double xiad,double traHeight):sd(shangd),xd(xiad),th(traHeight){}
    double sd,xd,th;
    virtual double Area()const{
        return (sd+xd)*th*0.5;
    }
};
int main(){

    Circle circle(12.6);
    Square square(3.5);
    Rectangle rectangle(4.5,8.4);
    Trapezoid trapezoid(2.0,4.5,3.2);
    Triangle triangle(4.5,8.4);
    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;
}