Thread: Linker Problem with virtual c++

I keep running into problem with the linker eventhough I already put the guard in the header files. Here're the errors that I get

here's the header

Code:

#ifndef __TANK__WAR__
#define __TANK__WAR__ 

#include <allegro.h>
#include <cstdlib>

int gameover = 0 ;

// Tank Structure



struct tagTank
{
	int x , y;
	int dir , speed;
	int color; 
	int score;
} tanks[2];

// Bullet Structure
struct tagBullet
{ 
	int x , y; 
	int alive;
	int xspd , yspd; 
} bullets[2];

... some code
#endif

Code:

1>------ Build started: Project: FirstAllegro, Configuration: Debug Win32 ------
1>TankWar.obj : error LNK2005: "struct tagBullet * bullets" (?bullets@@3PAUtagBullet@@A) already defined in main.obj
1>TankWar.obj : error LNK2005: "struct tagTank * tanks" (?tanks@@3PAUtagTank@@A) already defined in main.obj
1>TankWar.obj : error LNK2005: "int gameover" (?gameover@@3HA) already defined in main.obj
1>C:\Users\admin\Documents\Visual Studio 2010\Projects\FirstAllegro\Debug\FirstAllegro.exe : fatal error LNK1169: one or more multiply defined symbols found
========== Build: 0 succeeded, 1 failed, 0 up-to-date, 0 skipped ==========

What could cause this? I thought guard would overcome this error.

If you really must use global variables, declare them extern in the header, then define them in exactly one source file.

It works. thanks. I don't really like global variables either. But this is a program from an allegro book for game. I will change it later, too tired now to think.