/*
02.*煙臺大學計算機學院學生
03.*All right reserved.
04.*檔名稱*煙臺大學計算機學院學生
05.*All right reserved.
06.*檔名稱:抽象基類
07.*作者：王洪海
08.*完成日期：2013年6月12日
09.*版本號：v1.0
10.*對任務及求解方法的描述部分:抽象基類
11.*我的程式：
12.*/

/* C++程式碼 */
#include <iostream>

#include <iomanip>

using namespace std;

class Shape
{
 public:
  virtual double area() =0;
};

class Circle:public Shape
{
 public:
   Circle(double r):radius(r){}
   ~Circle(){}
   double area()
   {

       return 3.141596*radius*radius;
   }
 private:
   double radius;
};

class Rectangle:public Shape
{
 public:
   Rectangle(double l,double w):length(l),width(w){}
   ~Rectangle(){}
   double area()
   {
       return length*width;
   }
 private:
   double length;
   double width;
};

class Triangle:public Shape
{
 public:
   Triangle(double h,double d):height(h),down(d){}
   ~Triangle(){}
   double area()
   {
       return down*height*0.5;
   }
 private:
   double down;
   double height;
};

void printArea(Shape &n)
{
    cout<< setiosflags(ios::fixed)<<setprecision(2)<<n.area()<<endl;
}
int main()
{
    float r,a,b,w,h;
    cout<<fixed<<setprecision(2);
    cin>>r;
    Circle circle(r);
    cout<<"area of circle = ";
    printArea(circle);
    cin>>a>>b;
    Rectangle rectangle(a,b);
    cout<<"area of rectangle = ";
    printArea(rectangle);
    cin>>w>>h;
    Triangle triangle(w,h);
    cout<<"area of triangle = ";
    printArea(triangle);
    return 0;
}
 

執行結果，如下圖：

對抽象基類又熟悉了一次！！！