Get value from memcach but it is null - php

Question

I'm trying to get value from memcache.
value of $dataOld[$i] is null when I'm trying to read that in if statement outside of if block it contains right value.
This is my code.
My code is for get and send data .
any help will be much appreciated.
<?php
/**
* Created by PhpStorm.
* User: PC1
* Date: 9/18/2018
* Time: 11:57 AM
*/
include 'config.php';
include 'BefrestAuth.php';
include 'Publisher.php';
$memcahe = new Memcache();
$memcahe->connect("localhost", 11211);
$dataNew = json_decode($memcahe->get('keyNew'));
$memcahe->set('keyOld', json_encode($dataNew));
while (true) {
$dataNew = json_decode($memcahe->get('keyNew'));
$dataOld = json_decode($memcahe->get('keyOld'));
if (!$dataNew[0]->price) {
continue;
} else {
$str = "";
$taskolu = array();
for ($i = 0; $i < count($dataNew); $i++) {
if ((int)$dataNew[$i]->price > (int)$dataOld[$i]->price) {
echo "\n".$dataNew[$i]->price."/////".json_encode($dataOld[$i])."\n";
$str .= "name:" . $dataNew[$i]->name . " type:" . $dataNew[$i]->type . " price:" . $dataNew[$i]->price."\n";
array_push($taskolu, $dataNew[$i]);
}
if ((int)$dataOld->price > (int)$dataNew[$i]->price) {
$str .= "name:" . $dataNew[$i]->name . " type:" . $dataNew[$i]->type . " price:" . $dataNew[$i]->price."\n";
array_push($taskolu, $dataNew[$i]);
}
}
if (!empty($str)) {
$dbca = connection();
$dbca->set_charset("utf8");
$rate = "SELECT u.user_chid FROM users u";
$result = $dbca->prepare($rate);
$result->execute();
$res = $result->get_result();
while ($obj = $res->fetch_object()) {
$auth = (string)BefrestAuth::generatePublishAuth($obj->user_chid);
Publisher::publish(11812, $obj->user_chid, $auth, json_encode(array("messages" => $taskolu)));
echo "\n";
}
}
$memcahe->delete('keyOld');
$data=json_encode($dataNew);
$memcahe->set('keyOld', $data);
$dataOld = json_decode($memcahe->get('keyOld'));
}
}