Add custom fields from different posts

Question

I am trying to add up custom fields from different posts. The array I created is not working.

Here is the code.

<?php $totalpricearray = query_posts('post_type=items&author='.$thisauthorID.'&tag='.$thispostID); while (have_posts()) : the_post(); 

    $productprice = get_post_meta($post->ID, "productprice", true);
    $productquantity = get_post_meta($post->ID, "productquantity", true);
    $totalproductprice = ($productprice * $productquantity);
    echo $totalproductprice, ',';
         endwhile;

         $totalprice = array($totalpricearray);
         echo array_sum($totalprice); ?>

Any ideas,

Marvellous

(ps just noticed array is working but equals 0)

Answer 1

<?php
$totalprice_posts = get_posts('post_type=items&author='.$thisauthorID.'&tag='.$thispostID.'&numberposts=-1');
$totalprice_array = array();
foreach ($totalprice_posts as $post) {
    $productprice = get_post_meta($post->ID, "productprice", true);
    $productquantity = get_post_meta($post->ID, "productquantity", true);
    $totalproductprice = ($productprice * $productquantity);
    array_push($totalprice_array, $totalproductprice);
}
echo implode(',', $totalprice_array);
echo array_sum($totalprice_array);
?