C++问题，函数值传递问题？

Question

#include
using namespace std;
class Point
{
protected:
int x,y;
};

class Circle:public Point
{protected:
double r;
public:
double area();

};

double Circle::area()
{double area;
cout<<"请输入圆的半径r:";
cin>>r;
area=3.14*r*r;
return area;
}

class Cylinder:public Circle
{private:
double h;
public:
double area();
double volume();

};

double Cylinder::area()//求圆柱体的表面积
{
double barea;
cout<<"请输入圆柱的高:";
cin>>h;
barea=3.14*2*r*h+3.14*r*r*2;
return barea;
}

double Cylinder::volume()//求圆柱体的体积
{
double volume;
volume=3.14*r*r*h;
return volume;
}

int main()
{
Circle cir;
cout<<"圆的面积为："<<cir.area()<<endl;
Cylinder cy;
cout<<"圆柱体的表面积为："<<cy.area()<<endl;
cout<<"圆柱体的体积为："<<cy.volume()<<endl;
return 0;
}

Answer 1

Circle cir;
Cylinder cy;//这是两个对象 其在两个不同内存区域，cy 对象r值没有初始化。