pheasant pc lab

#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <ctype.h>
#define NMAX 1000
#define NULL_CHECK(p) if (p == NULL) return p;

char *pheasant(char *s) {
  char *res = NULL;
  char *token = strtok(s, " ");
  int n = strlen(token) + 2;
  res = calloc(n, sizeof(char));
  strcpy(res, token);
  res[n-2] = '-';
  NULL_CHECK(res);
  token = strtok(NULL, " ");
  while (token) {
    if (tolower(token[0]) == tolower(res[n - 4]) && tolower(token[1]) == tolower(res[n - 3])) {
      n += strlen(token) + 1;
      res = realloc(res, sizeof(char) * n);
      NULL_CHECK(res);
      strcat(res, token);
      strcat(res, "-");
    }
    token = strtok(NULL, " ");
  }
  res[n - 2] = 0;
  return res;
}

int main(void) {
  static char s[NMAX] = "Fazan antic";
  char *res = pheasant(s);
  if (res == NULL) {
    fprintf(stderr, "alloc error!\n");
    exit(-1);
  }
  puts(res);
  free(res);
  return 0;
}