C++习题 虚函数-计算图形面积

全部图形面积之和（结果保留两位小数）

#include <iostream>
#include<iomanip>
using namespace std;
class Shape
{
  public:
      virtual float area()=0;
      private:

};
class Circle:public Shape
{
public:
    Circle(float s)
    {r=s;
    }
float area(){return (3.1415926*r*r);}
    private:
        float r;

};

class Square:public Shape
{
public:
    Square (float s)
    {
     a=s;
    }
    float area() { return (a*a); }
private:
    float a;
};
class Rectangle :public Shape
{
public:
    Rectangle (float s,float d)
    {
     a=s;
     b=d;
    }
 float area() { return (a*b);}
private:
    float a,b;
};
class Trapezoid:public Shape
{
public:
    Trapezoid (float s,float d,float ss)
    {
     w1=s;
     w2=d;
     h=ss;
    }
    float area() { return ((w1+w2)*h/2); }
private:
    float w1,w2,h;
};
class Triangle:public Shape
{
public:
    Triangle (float s,float d)
    {
     w=s;
     h=d;
    }
    float area() { return (w*h/2); }
private:
    float w,h;
};


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;

}