Beginner's Problem With First Funtion

Hi, I'm working through the You Can Do It! book by Francis Glassborow and am stuck on the chapter that introduces functions. Can anyone tell me why this won't build?

Code:

#include <iostream>
#include "playpen.h"
#include "drawing_functions.h"

using namespace fgw;
using namespace std;

int main(){
 playpen paper;
 paper.scale(3);
 draw_a_cross(paper,-4,0,9,0,-4,9,black);
 paper.display();
 cout << "press return to end";
 cin.get();
 }

The drawing functions header I made and it contains:

Code:

#ifdef DRAWING_FUNCTIONS_H
#define DRAWING_FUNCTIONS_H

#include "playpen.h"

void draw_a_cross(fgw::playpen &,
 int left_of_cross_piece_x, int left_of_cross_piece_y,
 int width_of_cross,
 int bottom_of_cross_piece_x, int bottom_of_cross_piece_y,
 int height_of_cross,
 fgw::hue);

#endif

The playpen header makes all the paper and fgw stuff work fine. The IDE I'm using is Quincy. These are the errors I'm getting:
http://www.picvault.info/images/5370...ildproblem.bmp

Any help would be greatly appreciated.

playpen.h must include a prototype for the draw_a_cross function

It looks like playpen.h does include the prototype for draw_a_cross. I think the error is because drawing_functions.cpp does not #include "drawing_functions.h".

I'm not sure if this is the cause of the problem, but...

Code:

#ifdef DRAWING_FUNCTIONS_H
#define DRAWING_FUNCTIONS_H

Should be...

Code:

#ifndef DRAWING_FUNCTIONS_H
#define DRAWING_FUNCTIONS_H

Otherwise, DRAWING_FUNCTIONS_H is never defined, which might cause the function prototype never to be interpreted by the compiler.

Thanx maxhavoc that little "n" made all the difference! Thanks also to the others who replied.