Something

    check=0;

    printf("%s %s\n", inface, ifs->ifs_name);
    if (strncmp(inface,ifs->ifs_name,3)==0) {
      sprintf(procline,"%d %d",ifm.ifm_data.ifi_ibytes,ifm.ifm_data.ifi_obytes);
      check=1;
    }

	if (check==0) {
		printf("Requested interface \"%s\" not found.\n",inface);
		printf("Exiting...\n");
		exit(1);
	}