php if isset _GET id id _GET id else id id intval id if id id if catal

<?php
    if(isset($_GET["id"]))
        $id = $_GET["id"];
    else
        $id = 1;

    $id=intval($id);
    if(!$id)
    {
        $id=1;	
    }	
    if($catalog->checkCategory($id) == false)
        $id = 1;
    $catalog->createFilter($id);
    $catalog->filter->runFilter();
    $countgoods=$catalog->filter->countOfGoods();
    $checkbox=$catalog->filter->getAttributes();
?>