class circle
{
    protected:
        double r;
    public:
        circle(double radius=0) :r(radius){}
        double perimeter()
        {
            return 2 * pi * r;
        }
        double area()
        {
            return r * pi * r;
        }
};
class cylinder :public circle
{
protected:
    double hight;
public:
    cylinder(double radius=0,double height=0) :circle(radius),hight(height){}//初始化參數并提供默認值，radius只能由父類構造函數初始化
    double volume()
    {
        return area()*hight;
    }
};

//調用

　　cylinder cy(1,1);
　　cout<<cy.volume();