tranverse files under one directory using C++ on ubuntu

#include <string>
#include <iostream>
#include <stdlib.h>
#include <stdio.h>
#include </usr/include/i386-linux-gnu/sys/types.h>
#include </usr/include/i386-linux-gnu/sys/stat.h>
#include <dirent.h>
#include <errno.h>
using namespace std;
int main(void)

{
   DIR *dp;
   int n=0;
   int len=0;
   struct dirent *dirp;
   string str0;
   dp=opendir("/home/HSS/topic_modeling/topic_1/");

   while((dirp=readdir(dp))!=NULL)
   {   
      str0=string(dirp->d_name);
      len=str0.size();
      if( len>4) 
// for txt files and this will filter out the '.' and '..' file
      {
            // do what you want to do !
      }
   }
return 0;

}