我需要将代码放在HTML启动之前

got answer i need to place the code before the Html start

<?php
if (isset($_GET["id"]))
    {   
        $_SESSION['page']=$_GET["id"];
        $page = $_SESSION['page'];
    }
else
{
    $page = $_SESSION['page'];
    $tableName = $page."r"; 
}

?>