Help with a php echo and category number

Hey everyone
(hope this is in the right forum!)

Am trying to echo category numbers from the functions file.

Where $myString="6" in the functions file (6 being the cat number.)

It works in the following code on index.php

<a href="<?php echo get_category_link($myString);?>"><?php echo $myString; ?> </a>

But I cant get it to work in a loop query. I thought this would work…..

<?php query_posts('cat='<?php the_category($myString); ?>' &showposts=10'); ?>

But it doesnt. Would anyone have any ideas? Im really stuck as my PHP is pretty bad!! Thanks!