error LNK2001 inheritance problems - c++

Question

I am working on a homework problem where we have to use inheritance. (I'm not very good with inheritance yet). We are to make a parent class "card_games" that has two children classes called "gofish" and "poker". We are given a template that our main has to follow, and the rest of the design is up to us. Here is my header file: (called "classes.h")
#include <vector>
using namespace std;
struct cards{
int rank;
char suit;
};
class players{
public:
int points;
int active;
vector<cards> cardhand;
void printhand(players *gameplayers, int person);
};
class card_games{
protected:
players *gameplayers;
void player_make();
public:
virtual void play();
};
class poker :public card_games{
public:
void play();
};
class gofish :public card_games{
public:
void play();
};
void player0_play(players *gameplayers, cards *cardlist, int people);
void createdeck(cards *cardlist);
void shuffle(cards *cardlist);
void deal(cards *cardlist, int people, players *gameplayers);
int getplayers();
I have determined the error is something to do with my virtual call. The error specifically is:
cardgames_play.obj : error LNK2001: unresolved external symbol "public: virtual void __thiscall card_games::play(void)" (?play#card_games##UAEXXZ)
And I believe this causes my next error of:
card_games.exe : fatal error LNK1120: 1 unresolved externals
Anyway something is wrong with my virtual void function.
Here is my main function:
#include <iostream>
#include "classes.h"
int main(){
card_games *game;
int opt;
game = NULL;
cout << "Poker 1, Go Fish 2" << endl;
cin >> opt;
if (opt == 1)
game = new poker;
else if (opt == 2)
game = new gofish;
game->play();
return 0;
}
We are supposed to roughly use this template. If I understand it correctly, I am creating an instance of Card_game class called game, then assigning game to an instance of either gofish or poker. Then I dereference "game" to the "play();" function. The rest of my code, I have a
void gofish::play(){
blah blah
}
and a
void poker::play(){
blah blah
}
Which have the rest of my code that works.
Any help regarding this error is greatly appreciated. Thanks!
P.S. I am using visual studio 2013 on windows 8.

Answer 1

The method void play(); in card_games does not have a body, and it is not pure virtual. Just do the change:
class card_games{
protected:
players *gameplayers;
void player_make();
public:
virtual void play()=0; //make it pure virtual
};