Lifeform inheritance hierarchy

//currently only predator class
class fox : public living {
public:
   fox(int r, int c, int a = 0) : age(a)
      { row = r; column = c; }
   state  who() { return FOX; }
     //deferred method for foxes
   living*  next(world w);
protected:
   int  age;   //used to decide on dying
};

//currently only prey class
class rabbit : public living {
public:
   rabbit(int r, int c, int a = 0) : age(a)
      { row = r; column = c; }
   state  who() { return RABBIT; }
   living*  next(world w);
protected:
   int  age;
};

//currently only plant life
class grass : public living {
public:
   grass(int r, int c) { row = r; column = c; }
   state who() { return GRASS; }
   living* next(world w);
};

//nothing lives here
class empty : public living {
public:
   empty(int r, int c) { row = r; column = c; }
   state  who() { return EMPTY; }
   living*  next(world w);
};