Description
定义抽象类型Shape，由他派生三个类：Circle（圆形），Rectangle（矩形），Trapezoid（梯形），用一个函数printArea分别输出三者的面积。主函数已经给出，3个图形的数据在定义对象时给定，根据提示完成程序并提交。

注意：抽象类的定义及使用

主函数如下：

 

int main()
{
    Circle circle(12.6);
    cout<<"area of circle=";
    printArea(circle);
    Rectangle rectangle(4.5,8.4);
    cout<<"area of rectangle=";
    printArea(rectangle);
    Trapezoid trapezoid(4.5,8.4,8.0);
    cout<<"area of trapezoid=";
    printArea(trapezoid);
    return 0;
}
Input
无
Output

输出圆的面积

输出矩形面积

输出梯形面积

Sample Input
无
Sample Output
area of circle=498.759

area of rectangle=37.8

area of trapezoid=52.5

#include<iostream>
using namespace std;

const double PI=3.14159;

class Shape   //抽象类
{
protected:
    double x, y, z;
public:
    Shape(double d, double w=0,double z=0){x=d;y=w;this->z=z;}
    double getx() {return x;}
    double gety() {return y;}
    double getz() {return z;}
};

class Rectangle:public Shape
{
public:
    Rectangle(double d, double w=0,double z=0):Shape(d,w,z){}
};

class Circle:public Shape{
public:
   Circle(double d, double w=0,double z=0):Shape(d,w,z){}
};

class Trapezoid:public Shape{
public:
   Trapezoid(double d, double w=0,double z=0):Shape(d,w,z){}
};

void printArea(Circle c)
{
    cout<<PI*c.getx()*c.getx()<<endl;
}

void printArea(Rectangle r)
{
    cout<<r.getx()*r.gety()<<endl;
}
void printArea(Trapezoid t)
{
    cout<<(t.getx()+t.getz())*t.gety()/2.0<<endl;
}

int main()
{
    Circle circle(12.6);
    cout<<"area of circle=";
    printArea(circle);
    Rectangle rectangle(4.5,8.4);
    cout<<"area of rectangle=";
    printArea(rectangle);
    Trapezoid trapezoid(4.5,8.4,8.0);
    cout<<"area of trapezoid=";
    printArea(trapezoid);
    return 0;
}