WordPress list posts from sub categories

I’ve found this piece of code and it works:

<?php get_header(); ?>
<div id="job-listings">
<?php
            $category = get_the_category();
            $theName = $category[0]->name;
            $theChild = $category[0]->cat_ID;
$subcats = get_categories('child_of=" . $theChild);
    foreach($subcats as $subcat) {
    echo "<h3>' . $subcat->cat_name . '</h3>';
    echo '<ul>';
    $subcat_posts = get_posts('cat=" . $subcat->cat_ID);
    foreach($subcat_posts as $subcat_post) {
        $postID = $subcat_post->ID;
    echo "<li>';
    echo '<a href="' . get_permalink($postID) . '">';
    echo get_the_title($postID);
    echo '</a></li>';
    }
    echo '</ul>';
    } ?>
 </div>
 <?php get_footer(); ?>