#include <stdio.h>

/* substring locates a substring sub in a string s.
   If the substring is not found, it returns -1.
   If the substring is found, it returns the index in s
   where the substring is found.

   strncmp(s1,s2,n) compares the first n characters of two strings
   and returns 0 if they match.
*/
int substring( char *s, char *sub) {
  int i;

  for (i=0;i<strlen(s);i++) {
	if (strncmp(s+i,sub,strlen(sub))==0) 
	  return(i);
  }
  return(-1);
}

int main(int argc, char **argv) {
  int pos;

  if (argc<3) {
	printf("Usage: substring string sub\n");
	exit(1);
  }
  printf("Looking for %s in %s\n",argv[2],argv[1]);
  pos = substring(argv[1],argv[2]);
  if (pos==-1) 
	printf("Not found\n");
  else
	printf("found at position %d\n",pos);
  return(1);
}