Related Posts

// add to footer.php
<div class="recent-posts">
   <?php require_once( trailingslashit( get_template_directory() ). 'footer-posts.php' ); ?>
</div>

// create template part footer-posts.php

<?php if (is_page(4)) { ?> // show different title per page
  <img src="<?php bloginfo('template_directory'); ?>/images/recent-posts.png" alt="Recent Posts">
<?php } else { ?>
   <img src="<?php bloginfo('template_directory'); ?>/images/related-posts.png" alt="Related Posts">
<?php } ?>
<?php //wp_nav_menu( array('menu' => 'footer-main' )); ?>

<ul>
<?php $ID = get_the_ID(); //get the current page ID
      //single page per category
      //x => y
      //category ID => page ID
      $pages = array( 
         "17" => "105", //botox
         "8" => "67", //breastaug
         "20" => "69", //breastlift
         "16" => "91", //buttlift
         "9" => "55", //cosmeticsurgery
         "11" => "89", //tummytuck
         "15" => "58", //recovery
         "13" => "113", //facialplasticsurgery
         "10" => "53", //plasticsurgery
         "21" => "93", //postbariatric
         "14" => "132", //skincare
      );
      //multiple pages per category
      $bs = array("99","79","77","87","95","97","103" ); //bodysurgery
      $cs = array("55","126","128","130","708","111"); //cosmeticsurgery
      $fps = array("113","115","117","124","122","126","128","130"); //facialplasticsurgery
      $sc = array("176","607","107","109","621","141","605","132"); //skincare
      $mps = array("180","75","73"); //maleplasticsurgery
      $fit = array("143","172","17"); //fitness
      
      //if the ID is in the single page array
      if (in_array($ID, $pages)) {
         //search for the ID in the single page array, return the key (category ID)
         $cat = array_search($ID,$pages);
         
         if ($cat != false) {
            if (is_page(4)) {
               //show recent posts on homepage
               $the_query = new WP_Query( 'posts_per_page=3' );
            } else {
               //show posts by selected category
               $the_query = new WP_Query( 'posts_per_page=3&cat=' . $cat );
            }
         }
      //if the ID is in multi page array
      } else if (in_array($ID, $bs)) {
         //bodysurgery category
         $cat = "18";
         $the_query = new WP_Query( 'posts_per_page=3&cat=' . $cat );

      } else if (in_array($ID, $cs)) {
         //cosmeticsurgery category
         $cat = "9";
         $the_query = new WP_Query( 'posts_per_page=3&cat=' . $cat );

      } else if (in_array($ID, $fps)) {
         //facialplasticsurgery category
         $cat = "13";
         $the_query = new WP_Query( 'posts_per_page=3&cat=' . $cat );

      } else if (in_array($ID, $sc)) {
         //skincare category
         $cat = "14";
         $the_query = new WP_Query( 'posts_per_page=3&cat=' . $cat );

      } else if (in_array($ID, $mps)) {
         //maleplasticsurgery category
         $cat = "12";
         $the_query = new WP_Query( 'posts_per_page=3&cat=' . $cat );

      } else if (in_array($ID, $fit)) {
         //fitness category
         $cat = "19";
         $the_query = new WP_Query( 'posts_per_page=3&cat=' . $cat );

      } else {
         //no category, recent posts only
         $the_query = new WP_Query( 'posts_per_page=3' );
      }

      $cat_name = get_cat_name( $cat ); //get cat name by category ID
      $cat_name = preg_replace('/\s+/', '', $cat_name); //remove spaces from category name

      while ($the_query -> have_posts()) : $the_query -> the_post(); ?>

      <li class="<?php echo $cat_name ?>"><a href="<?php the_permalink() ?>"><?php the_title(); ?></a><br><?php the_excerpt(__('(more…)')); ?></li>

<?php 
endwhile;
wp_reset_postdata();
?>
</ul>