【说明】
以下C++程序的功能是计算三角形、矩形和正方形的面积并输出。程序由4个类组成：类Triangle、Rectangle和Square分别表示三角形、矩形和正方形；抽象类Figure提供了一个纯虚拟函数getArea()，作为计算上述3种图形面积的通用接口。
#include＜iostream.b＞
#include＜math.h＞
class Figure
public:
virtual double getArea0=0; //纯虚拟函数
;
class Rectangle: (1)
protected:
double height;
double width;
public:
Rectangle();
Rectangle(double height, double width)
This-＞height=height;
This-＞width=width;
double getarea()
return (2) ;
;
class Square: (3)
public:
Square(double width)
(4) ;
;
class Triangle: (5)
double la;
double lb;
double lc;
public:
Triangle(double la, double lb, double lc)
this-＞la=la; this-＞lb; this-＞lc;
double getArea()
double s=(la+lb+lc)/2.0;
return sqrt(s*(s-l
- a)**(s-l
- b)*(s-l
- c));
;
viod main()
Figure* figures[3]=
new Triangle(2,3,3), new Rectangle(5,8), new Square(5));
for(int i=0;i＜3;i++)
cout＜＜"figures["＜＜i＜＜"]area="＜＜(figures[i])-＞getarea()＜＜endl;