C++菜鸟，为什么这个输出带nan，烦死了.....

#include
#include
using namespace std;
#define PI 3.14
class Base{
protected:
    double r;
public:
    Base(double a=1)
    {
        r=a;
    }
};
class Sphere:public Base{
public:
    Sphere(double a=1):Base(a){}
    double getSpheres()
    {
        return 4*PI*r*r;
    }
    double showSpheres()
    {
        cout<<"The area of the sphere:"<    }
};
int main()
{
    double a1;
    cout<<"Input the radius of the sphere:";
    cin>>a1;
    Sphere x(a1);
    cout<

}