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。
所有图形面积之和（结果保留两位小数）
12.6 3.5 4.5 8.4 2.0 4.5 3.2 4.5 8.4
total of all areas=574.11
#include <iostream>
#include <iomanip>
using namespace std;
class Shape
{
public:
virtual double area() const=0;
};
class Circle:public Shape
{
public:
Circle(double r):radius(r){}
virtual double area() const{return 3.14159*radius*radius;}
protected:
double radius;
};
class Rectangle:public Shape
{
public:
Rectangle(double r,double l):width(r),height(l){}
virtual double area() const{return width*height;}
protected:
double width;
double height;
};
class Triangle:public Shape
{
public:
Triangle(double r,double l):width(r),heigth(l){}
virtual double area() const{return 0.5*width*heigth;}
protected:
double width;
double heigth;
};
class Trapezoid:public Shape
{
public:
Trapezoid(double r,double l,double k):top(r),bottom(l),height(k){}
virtual double area() const{return 0.5*(top+bottom)*height;}
protected:
double top;
double bottom;
double height;
};
class Square:public Shape
{
public:
Square(double r):side(r){}
virtual double area() const{return side*side;}
protected:
double side;
};
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;
} 原文地址：http://blog.csdn.net/u013629228/article/details/29561505
