What function displays comments number?

i have some recent posts titles in sidebar with this code

<div class="sdb-content">
		<h3>Hardware Apžvalgos</h3>
<ul>
<?php
$posts = get_posts('numberposts=5&category=31,32,36');
foreach($posts as $post) :
?>
<li>
<a href="<?php the_permalink(); ?>"><?php the_title() ?></a>
</li>
<?php endforeach; ?>
</ul>
</div>

i would like to add a comments number for each post, what function should i use?
<a href="<?php the_permalink(); ?>"><?php the_title() ?> (<? comments_popup_link ?>)</a>
doesn’t work in sidebar