如何通过在PHP中使用cookie来查看用户是否已经看到弹出信息？

I make popup box to show user about my website information by using jquery ui. Now, I want to show this popup box to every user that are registered or not when they open my website.

so, I create two php script file like static.php and dynamic.php to show popup box to user. dynamic.php for the registered user and static.php for non register user.

I have no problem in dynamic.php. For static.php, I create cookie to check if the user is already answer or not. But its not working. Here is my code.

$cookie = "";
$rnd_cookie="";
if(isset($_COOKIE['user_id']) && $_COOKIE['user_id']==$cookie) { 
    echo "this static user already answer<br/>";    
    echo "cookie ".$_COOKIE['user_id']."<br/>";
    echo "check_cookie ".$cookie."<br/>";
} else {                    
    $rnd_cookie = rand()*1000;
    setcookie("user_id",$rnd_cookie,time()+28800);//expire time 8 hrs
    echo "create cookie value: $rnd_cookie<br/>";
    echo "cookie: ".$_COOKIE['user_id']."<br/>";
    $cookie = $_COOKIE['user_id'];

    check();
}

After searching about my problem, I know the problem that is I can't get cookie value immediately after setting cookie like this,

setcookie("user_id",$rnd_cookie,time()+28800);//expire time 8 hrs
$cookie = $_COOKIE['user_id'];

I have no idea how to check user can see popup or not with cookie. I very appreciate for any suggestion.