OJ 1.H

/*
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。 

Input
圆的半径
正方形的边长
矩形的边长
梯形的上底和下底，高
三角形的底与高

Output
所有图形面积之和（结果保留两位小数）




*/
#include <iostream>
#include <iomanip>
#define PI 3.1415926
using namespace std;
class Shape
{
    public:
     virtual double area()=0;
};
class Circle:public Shape//（圆形）
{
    public:
    Circle():Shape(){}
    Circle(double a):r(a){}
    double area()
    {
        return r*r*PI;
    }
    private:
    double r;
};
class Rectangle:public Shape//（矩形）
{
     public:
      Rectangle():Shape(){}
    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():Shape(){}
     Triangle(double a,double b):y(a),n(b){}
    double area()
    {
        return (y*n)/2;
    }
    private:
    double y;
    double n;
};
class Square:public Shape//Square(正方形)
{
    public:
    Square():Shape(){}
    Square(double c):m(c){}
    double area()
    {
        return m*m;
    }
    private:
    double m;
};
class Trapezoid:public Shape//Trapezoid(梯形)
{
     public:
    Trapezoid():Shape(){}
    Trapezoid(double c,double g,double h):i(c),o(g),p(h){}
    double area()
    {
        return ((i+o)*p)/2;
    }
    private:
    double i;
    double o;
    double p;
};
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;
}