CArray's / Polymorphism

Greetings,
    I'm having trouble with implementing a CArray for the purpose of polymorphism. I've written the little program to illustrate my problem (I'm using VC 6.0).
    Basically I have a base class (in this case animal) and I have lots of other classes that want to inherit those properties (dog, cat, bird). I then want to talk about a group of the derived classes (zoo) which uses polymorphism. My issue is that VC won't compile it and for the life of me I can't figure out why.
<START CODE>
#include "Afxtempl.h"
#include <stdio.h>


class animal
{
protected:
     int legs;
public:
     void NumLegs(void) { printf("I have %d legs\n", legs); }
     virtual void speak(void) { };
};

class dog : public animal
{
public:
     dog() { legs = 4; }
     void speak(void) { printf("Woof\n"); }
};


class cat : public animal
{
public:
     cat() { legs = 4; }
     void speak(void) { printf("Meow\n"); }
};

class bird : public animal
{
public:
     bird() { legs = 2; }
     void speak(void) { printf("Chirp\n"); }
};

class zoo
{
public:
     CArray<animal *, animal *> animals;
     void AddAnimal(animal *a);
     void FreeAnimals(void);
     void ListAnimals(void);
};

void zoo::AddAnimal(animal *a)
{
     animals.Add(a);
}

void zoo::FreeAnimals(void)
{
     animal *a;

     for(int c; c < animals.GetSize(); c++) {
          a = animals.ElementAt(c);
     }
}

void zoo::ListAnimals(void)
{
     animal *a;

     for(int c; c < animals.GetSize(); c++) {
          a = animals.ElementAt(c);
          a->NumLegs();
          a->speak();
     }

}

int main(int argc, char* argv[])
{
     zoo *z = new zoo;    

     animal *a = new dog;
     animal *b = new cat;
     animal *c = new dog;
     animal *d = new bird;
     animal *e = new dog;
     

     z->AddAnimal(a);
     z->AddAnimal(b);
     z->AddAnimal(c);
     z->AddAnimal(d);
     z->AddAnimal(e);
     z->ListAnimals();

     z->FreeAnimals();

     delete(z);

     return 0;
}
<END CODE>
These are the compilation errors...

--------------------Configuration: polymorphism - Win32 Debug--------------------
Compiling...
polymorphism2.cpp
Linking...
nafxcwd.lib(thrdcore.obj) : error LNK2001: unresolved external symbol __endthreadex
nafxcwd.lib(thrdcore.obj) : error LNK2001: unresolved external symbol __beginthreadex
Debug/polymorphism.exe : fatal error LNK1120: 2 unresolved externals
Error executing link.exe.

polymorphism.exe - 3 error(s), 0 warning(s)

The issues go away is you comment out the CArray definition in zoo (and the references to animals from the memeber functions), but what is wrong with the definition?? All I want is an array of animals (zoo, referred to by pointers) so that I can add more 'animals' and not have to worry too much about what they are.

Kind Regards

Fluffy Checkers