Find 2 letter commands under all bin directory

/* finds recursively files having 2-letters name in directories whoose name ends with 'bin'
  usage:
    rd [<DIRNAME>]

  on <DIRNAME> missing, current directory is used
*/

#include <string.h>
#include <stdio.h>
#include <sys/types.h>
#include <unistd.h>
#include <dirent.h>

#define BUFSIZE 0x400

int has_slash(const char * buf, size_t len);

int rd(const char * nam, int check)
{
  char buf[BUFSIZE];

  DIR * d = opendir(nam);

  if (d)
  {
    struct dirent *entry;
    while   ((entry = readdir(d)) != NULL)
    {
      if ( check && entry->d_type == DT_REG )
      {
        if (strlen(entry->d_name)==2)
        {
          printf("%s/%s\n", nam, entry->d_name);
        }
      }

      if (entry->d_type == DT_DIR)
      {
        int check;
        int len;
        strcpy( buf, nam );
        if ( ! has_slash(nam, strlen(nam)))
          strcat(buf, "/");
        strcat(buf, entry->d_name);
        len = strlen(entry->d_name);
        check =  ! strncmp( &entry->d_name[len-3], "bin", 3);
        if ( strcmp(".", entry->d_name) && strcmp("..", entry->d_name))
          rd(buf, check);
      }
    }
  }
  closedir(d);
  return 0;
}

int has_slash(const char * buf, size_t len)
{
  if ( len < 1) return 0;
  if ( buf[len-1] == '/' ) return 1;
  return 0;
}

int is_bin(const char * buf, size_t len)
{
  if ( has_slash( buf, len) )
  {
    len--;
  }
  if ( len < 3)
    return 0;
  else if ( len == 3 )
  {
    if ( ! strncmp(buf, "bin",3))
      return 1;
  }
  else
  {
    if ( !strncmp(&buf[len-4], "/bin", 4))
      return 1;
  }
  return 0;
}
int main (int argc, char * argv[])
{
  char buf[BUFSIZE];

  if (argc > 1)
  {
    strncpy(buf, argv[1], BUFSIZE-1);
    buf[BUFSIZE-1] = '\0';
  }
  else
  {
    getcwd(buf, sizeof(buf));
  }

  rd( buf, is_bin(buf, strlen(buf)));

  return 0;
}