grpck.c: In function 'main':
grpck.c:230:22: error: comparison between pointer and integer [-Werror]
   for (i = 0; buf[i] != NULL; i++) {
                      ^~
grpck.c:289:10: error: assignment makes integer from pointer without a cast [-Werror=int-conversion]
    *cptr = NULL;
          ^
grpck.c:290:14: error: comparison between pointer and integer [-Werror]
    if (*nptr == NULL) {
              ^~
cc1: all warnings being treated as errors