OJ嘻唰唰虚函数-计算图形面积

Description

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）

Sample Input

12.6
3.5
4.5 8.4
2.0 4.5 3.2
4.5 8.4

Sample Output

total of all areas=574.11

代码：

#include <iostream>
#include <iomanip>
using namespace std;
class  Shape
{
public:
virtual double area()=0;
};
class Circle:public Shape
{
public:
Circle(double r=0):radius(r){}
double area()
{
return 3.1415926*radius*radius;
}
protected:
double radius;
};
class Square:public Shape
{
public:
Square(double l=0):longth(l){}
double area()
{
return longth*longth;
}
protected:
double longth;
};
class Rectangle:public Shape
{
public:
Rectangle(double w=0,double h=0):width(w),height(h){}
double area()
{
return width*height;
}
protected:
double width;
double height;
};
class Trapezoid:public Shape
{
public:
Trapezoid(double s=0,double x=0,double g=0):shang(s),xia(x),gao(g){}
double area()
{
return (shang+xia)*gao/2;
}
protected:
double shang;
double xia;
double gao;
};
class Triangle:public Shape
{
public:
Triangle(double b=0,double h=0):base(b),height(h){}
double area()
{
return base*height/2;
}
protected:
double base;
double height;
};

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;

}

运行结果：