Thread: Derived class can't declare

Ok, somehow i think this is weird. I'm gonna summarized my whole code:

Code:

class Sphere;
class Rectangle;
class Segment;


class Body
{
   public: 
   vect2 Velocity, Position;
   float mass
     Body(){}
     //then other stuff and functions will go on
   //I also have some virtual bool function in here named "Collision"
};

class Sphere: public Body
{
public:
   float Radius;
   Sphere(){}
   //Then the collision functions will go on

};

So that's basically it. Then when i tried to do this:

Code:

Sphere ball;

it gave an error like this:

Code:

error C2259: 'Sphere' : cannot instantiate abstract class due to following members:
see declaration of 'Sphere'

Can someone help me out here?