error

Hi.I am using writing a program and keil show me this error:
error: #28: expression must have a constant value
The program:
#ifndef __ov7670_H
#define __ov7670_H

#include <stdio.h>
#include <stdint.h>

#include "ov7670reg.h"

uint8_t HEIGHT,WIDTH;
int x,y;
uint16_t frame1[ HEIGHT * WIDTH ];
uint16_t frame2[ HEIGHT * WIDTH ];
uint32_t ov7670_set(uint8_t addr,uint8_t val);
uint8_t ov7670_get(uint8_t addr);
void ov7670_init(void);
void ov7670_readframe(void);
void ov7670_clear_buffer(void);
void ov7670_check_missing(void);
The error is from bold part!!!!!!!!
What should i do?
Thanks