text: #include <stdio.h>
  #include <string.h>
  int reserve(int num, char * chr)
  {
      int head = 0, tail = num - 1;
      int count = num / 2;
  
      count--;
      if (count < 0)
          return 0;
      else
      {
          *(chr + head) ^= *(chr + tail);
          *(chr + tail) ^= *(chr + head);
          *(chr + head) ^= *(chr + tail); 
      }
      return reserve(num - 2, chr + 1);
  }
  int main(void)
  {
      char buf[6] = {0};
  
      printf("Please enter 6 characters: ");
      fgets(buf, 6, stdin);
      reserve(strlen(buf), buf);
      printf("Output reslut in reserved order: ");
      printf("%s \n", buf);
  
      return 0;
  }