ok, this is a better place to make my question:
I have this piece of code- basically is a select (dropdown menu) where the options are within a while sentence. Now I need to set one as default, but I can't figure out how to do it

Here the code goes:
echo '<select name="topic_cat">';
while($row = mysql_fetch_assoc($result))
{
echo '<option value="' . $row['cat_id'] . '">' . $row['cat_name'] . '</option></select><br />';
}
and I want the selected (default) one to be called $topic_cat where cat_id = topic_cat
FYI this is part of editing a post which is already made.
Any idea?
Thanks!!