splitting files in C- Segmentation fault - c

Question

I'm new to the subject of splitting files and header files in C.
I get a Segmentation fault (core dumped) when i'm trying to run main. I don't get any more errors.
I tried to trace the problam and I think it is the line:
syntax_check(fp, symb_table, &IC, &DC); in the main.c.
I'm just trying to pass from main.c the parameters *fp and another array strcture(symbol[]) to a function in syntax_check(in syntax_check.c) and do some actions.
main.c:
#include "main.h"
int main()
{
FILE *fp;
int DC=0;
int IC=100;
symbol symb_table[20];
if (!(fp=fopen("file.txt", "r")))
{
printf("Error opening file");
exit(0);
}
syntax_check(fp, symb_table, &IC, &DC);
fclose(fp);
return 0;
}
main.h:
#include <stdlib.h>
#include <stdio.h>
typedef struct {
char name[10];
int address;
int external;
int action;
} symbol;
int syntax_check(FILE*, symbol[], int*, int*);
syntax_check.c:
#include "syntax_check.h"
int syntax_check(FILE *fp, symbol symb_table[], int *IC, int *DC)
{
char buff[80]; /*line to read*/
char buff2[20]; /**/
int i=0;
fgets (buff, 80, fp);
while (buff[i]!='\0'||buff[i]!=' '||buff[i]!='\t')
{
buff2[i]=buff[i];
i++;
}
buff[i]='\0';
if (exist(buff2))
printf("legal");
else
printf("illegal");
return 0;
}
syntax_check.h:
#include <stdlib.h>
#include <stdio.h>
typedef struct {
char name[10];
int address;
int external;
int action;
} symbol;
FILE *fp;
int exist(char action[]);