补充完整下面的类定义:
const double PI=3.14;
class circle{ //圆形物体的抽象基类
protected:
double r; //半径
public:
Circle(double radius=0):r(radius){}
______; //计算圆形物体表面积的纯虚函数声明
};
class Cylinder: public Circle { //圆柱体类
double h;//高度
public:
Cylinder(double radius=0,double height=0):
Circle(radius),h(height){}
virtual double Area( ){ //计算圆柱体的表面积
return 2*PI*r*(r+h);
}
};