How to show related posts by category

The question has already been asked and the answer has been posted too,

How to display related posts from same category?

Add this code inside your single.php after a loop wherever you want to show related post,

<?php

$related = get_posts( array( 'category__in' => wp_get_post_categories($post->ID), 'numberposts' => 5, 'post__not_in' => array($post->ID) ) );
if( $related ) foreach( $related as $post ) {
setup_postdata($post); ?>
 <ul> 
        <li>
        <a href="https://wordpress.stackexchange.com/questions/41272/<?php the_permalink() ?>" rel="bookmark" title="<?php the_title(); ?>"><?php the_title(); ?></a>
            <?php the_content('Read the rest of this entry &raquo;'); ?>
        </li>
    </ul>   
<?php }
wp_reset_postdata(); ?>

It will display related post from the same category with the post excerpt and title ,
however if want this code to display just the title of related post then remove this line,

<?php the_content('Read the rest of this entry &raquo;'); ?>