Putting Adsense without Single.Php

I’m new to WP, and I’ve run into a problem.

I want to put adsense code in so that the ad appears inline with the post on it’s individual page (ie. the comment page) not on the front page.

I’ve read that I can put the code in the single.php file… except that the theme I’m using doesn’t have a single.php file. it has:
comments-popup.php
comments.php
footer.php
header.php
index.php
sidebar.php
style.css
but no single.php

So how do i go about inserting the adsense code into the individual page without a single.php file? Please help.