Write unix mv function in C

mvc.c

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <errno.h>
#include <dirent.h>
 
int main(int ac, char *av[]){
 
  errno = 0;
  int result = 0;
  DIR *dir;
  char buf[512];
  
  if(ac == 3){
    dir = opendir(av[2]);
    
    if(dir){
      char *pch;
      pch = strrchr(av[1], '/');
      if(pch == NULL) sprintf(buf, "%s/%s", av[2], av[1]);
      else sprintf(buf, "%s/%s", av[2], pch+1);
      result = rename(av[1], buf);
    }
    else{
      result = rename(av[1], av[2]);
    }
    
    if(result==-1){
      fprintf(stderr, "%s Cannot move from %s to % s\n%s\n", av[0], av[1], av[2], strerror(errno));
      exit(EXIT_FAILURE);
    }
    
  }else {
    fprintf(stderr, "SYNTAX ERROR:\nUsage: %s [Old file name] [New file name]\n", av[0]);
    exit(EXIT_FAILURE);
  }
 
  return 0;
}