ganesh@ubuntu:~/my_programs/c$ cat main.c
# include "fnhash.h"
# include <stdio.h>

int main(int argc, char *argv[])
{
	if(argc!=2)
	{
		printf("Usage wrong");
		exit(1);
	}

	FILE *fp;
	if((fp=fopen(argv[1],"r"))==NULL)
	{
		printf("File opening error\n");
		exit(1);
	}

	char *instr;
	char hashnum[100];

	while(!feof(fp))
	{
		while(fscanf(fp,"%s",instr)>0)
		{
			printf("in Number Length : %lu\n",strlen(instr));
			instr[strlen(instr)+1]='\0';
			printf("in Number = %s\n",instr);
			fnhash(instr,hashnum);
			printf("in number : %s\tHashed value : %s\n",instr,hashnum);
		}
	}

	return 0;
}

ganesh@ubuntu:~/my_programs/c$ cat fnhash.c
# include <stdio.h>
# include <stdlib.h>
# include <string.h>
# include "fnhash.h"

void fnhash(const char nbr[],char hsh[])
{
	char *tmpnbr, *tmphsh;
	tmpnbr=nbr;
	tmphsh=hsh;
	char a;
	char b;
	while(*tmpnbr!='\0')
	{
		a=('A'-*tmpnbr)+'A';
		b=('z'+*tmpnbr)-'A';
		sprintf(tmphsh,"%d%c%c",*tmpnbr,a,b);
		tmpnbr++;
		tmphsh=tmphsh+4;
	}
	printf("strlen of hashed value = %lu\n",strlen(hsh));
	tmphsh[strlen(tmphsh)+1]='\0';
	return;
}

ganesh@ubuntu:~/my_programs/c$ cat numbers.lst
1234567890123456
12345678901234567
1234567890123456789
123456

ganesh@ubuntu:~/my_programs/c$ make -f hashmake
gcc -Wall -g -c main.c
main.c: In function ‘main':
main.c:9: warning: implicit declaration of function ‘exit'
main.c:9: warning: incompatible implicit declaration of built-in function ‘exit'
main.c:16: warning: incompatible implicit declaration of built-in function ‘exit'
main.c:26: warning: implicit declaration of function ‘strlen'
main.c:26: warning: incompatible implicit declaration of built-in function ‘strlen'
main.c:26: warning: ‘instr' may be used uninitialized in this function
gcc -Wall -g main.o fnhash.o -o main

ganesh@ubuntu:~/my_programs/c$ ./main numbers.lst
in Number Length : 16
in Number = 1234567890123456
Segmentation fault (core dumped)

ganesh@ubuntu:~/my_programs/c$ gdb main core
GNU gdb (GDB) 7.1-ubuntu
Copyright (C) 2010 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.  Type "show copying"
and "show warranty" for details.
This GDB was configured as "x86_64-linux-gnu".
For bug reporting instructions, please see:
<http://www.gnu.org/software/gdb/bugs/>...
Reading symbols from /home/ganesh/my_programs/c/main...done.
[New Thread 3605]

warning: Can't read pathname for load map: Input/output error.
Reading symbols from /lib/libc.so.6...(no debugging symbols found)...done.
Loaded symbols for /lib/libc.so.6
Reading symbols from /lib64/ld-linux-x86-64.so.2...(no debugging symbols found)...done.
Loaded symbols for /lib64/ld-linux-x86-64.so.2
Core was generated by `0645Uf49Qj49Qj56Jq'.
Program terminated with signal 11, Segmentation fault.
#0  0x00007f578f8fbb87 in vsprintf () from /lib/libc.so.6