习题：计算圆柱表面积和体积

个人答案：

#include 
#include 
#define PI 3.1415926
using namespace std;
class Circle
{
public:
  Circle(double,double);//声明构造函数
  double Volume();
  double Area();
  friend void display( Circle&);//声明display函数
private:
  double radius;
  double height;
};
Circle::Circle(double r,double h)
{
  radius = r;
  height = h;
}
double Circle::Volume()
{
  return PI * radius * radius * height;
}
double Circle::Area()
{
  return 2 * PI * radius * radius + 2* PI* radius * height;
}
void display( Circle&c1)
{
  cout << "圆柱的表面积:  " < 
结果：