<?php
session_start();
$siteler = array(1=>"google.com",2=>"yahoo.com",3=>"bing.com" ,4=>"mynet.com");
// $rand = rand (1,4);
$_SESSION["rand"] = isset($_SESSION["rand"]) ? $_SESSION["rand"] : 1;

$rand = $_SESSION["rand"];
header("location:http://www.".$siteler[$rand]);

$_SESSION["rand"]++;
if($_SESSION["rand"]>4){
    $_SESSION["rand"] = 1;
}
?>