[急求]使用虚函数编写程序求球体和圆柱体的体积及表面积.由于球体和圆柱体都可以看作由圆继承而来,所

#include
const double PI=3.14159265;
class circle
{ public:
circle(double r) { radius = r; }
virtual double area() { return 0.0; }
virtual double volume() { return 0.0; }
protected:
double radius;
};
class sphere:public circle
{ public:
sphere( double r ):circle( r ){ }
double area() { return 4.0 * PI * radius * radius; }
double volume()
{ return 4.0 * PI * radius * radius * radius / 3.0; }
};
class column:public circle
{ public:
column( double r,double h ):circle( r ) { height = h; }
double area()
{ return 2.0 * PI * radius * ( height + radius ); }
double volume()
{ return PI * radius * radius * height; }
private:
double height;
};
void main()
{ circle *p;
sphere sobj(2);
p = &sobj;
cout