PHP/MySQL update a news record in a database problem

<?php
    $title = "Edit News";
    include("../includes/header.php");
    include("../includes/database.php");
    $done = false;
    $expected = array('newstitle', 'newscontent', 'id');
    if ($_GET && !$_POST) {
    	if (isset($_GET['id']) && is_numeric($_GET['id'])) {
    		$id = $_GET['id'];
    	}
    	else {
    		$id = NULL;
    	}
    	if ($id) {
    		$sql = "SELECT * FROM news WHERE id = $id";
    		$result = mysql_query($sql) or die ("Error connecting to database...");
    		$row = mysql_fetch_assoc($result);
    	}
    	// if form has been submitted, update record
    	if (array_key_exists('update', $_POST)) {
    		// prepare expected items for insertion into database
    		foreach ($_POST as $key => $value) {
    			if (in_array($key, $expected)) {
    				${$key} = mysql_real_escape_string($value);
    			}
    		}
    		// abandon the process if primary key invalid
    		if (!is_numeric($id)) {
    			die('Invalid request');
    		}
    		// prepare the SQL query
    		$query = "UPDATE news SET title = '$title', content = '$content' WHERE id = $id";
    		// submit the query
    		$done = mysql_query($query) or die("Error connecting to database...");
    	}
    }
    // redirect page if $id is invalid
    if ($done) {
    	header("Location: $ROOT/admin/listnews.php");
    	exit;
    }
?>

if ($_GET && !$_POST) {

if (array_key_exists('update', $_POST)) {

// prepare the SQL query
$query = "UPDATE news SET title = '$newstitle', content = '$newscontent' WHERE id = $id";

if (array_key_exists('update', $_POST)) {

if (array_key_exists('update', $_POST)) {
...
}

if (count($_POST) && array_key_exists('update', $_POST)) {
...
}