[Opserty]

You could make use of vB's functions, let it do the hard work for you

PHP Code:

// If $thread doesn't work, try $post or try $foruminfo
$parents = fetch_forum_parent_list($thread['forumid']); 

// You may need to use array_map('trim', explode(',', $parents)); if that works though
$parents = explode(',', $parents); 

if(in_array('341', $parents))
{
    // $show_ads_in_this_forum = true; ?
}