php how can set counter limit?

<?php
class instaAuth
{
    public function _userlistesi() {
        $klasor = opendir("cookieboq/");
        while(false !== ($veriler = readdir($klasor))) {
            if(strstr($veriler,'txt')) {
            $bir_veri = str_replace('.txt','',$veriler);
            $user_ekle .= "$bir_veri,";
        }
    }...