How to modify xml data using php - Part 2

Use the following code to update the submitted value from modify.php into xml:
<?php

function update_book_id($id, $filename = 'loaned.xml')

{

$data = simplexml_load_file($filename);

for($i = 0, $length = count($data->resource->book); $i < $length; $i++)

    {

    if($data->resource->book[$i]->ID == $id)

        {

       

        $btitle = $_POST['btitle'];        

        $bdate = $_POST['bdate'];

        $bookrentdate = $_POST['bookrentdate'];

        $booksid = $_POST['booksid'];

       

        $data->resource->book[$i]->title = $btitle;

        $data->resource->book[$i]->date = $bdate;

        $data->resource->book[$i]->retdate = $bookrentdate;

        $data->resource->book[$i]->SID = $booksid;

        break;

        }

    }

    file_put_contents($filename, $data->saveXML());

    //echo $deletingbook." Deleted !!!";

}

//SAMPLE USAGE

$updatingbook = $_POST['bid'];

echo $updatingbook;

update_book_id ($updatingbook);

header("Location:index.php");  

//delete_book_id('Book 1');

?>