Next / previous node links in Drupal 7

custom-case-2.php

    switch($n_node->type) {	
      case 'your-custom-content-type-machine-name-here': 
        $html = l('"'.$n_node->title .'"', 'node/'.$n_node->nid, array('html' => TRUE, 'attributes' => array('class' => array('prev-next'), 'title' => $n_node->title)));
      return $html; 
    }

custom-case.php

    switch($n_node->type) {	
      case 'your-custom-content-type-machine-name-here': 
        $html = l('"'.$n_node->title .'"', 'node/'.$n_node->nid); 
      return $html; 
    }

node--2.tpl.php

<?php 
$nextPost = pn_node($node, 'n'); 	
$prevPost = pn_node($node, 'p'); 	

if ($nextPost != NULL) { ?>
  <?php print $nextPost; ?>
<?php } ?>

<?php if ($prevPost != NULL) { ?>
  <?php print $prevPost; ?>
<?php } ?>

node.tpl.php

<ul>
  <li><?php print pn_node($node, 'n'); ?></li>
  <li><?php print pn_node($node, 'p'); ?></li>	
</ul>

template-2.php

function pn_node($node, $mode = 'n') {
  if (!function_exists('prev_next_nid')) {
    return NULL;
  }

  switch($mode) {
    case 'p':
      $n_nid = prev_next_nid($node->nid, 'prev');
        $link_text = 'previous';
      break;
  	
    case 'n':
      $n_nid = prev_next_nid($node->nid, 'next');
      $link_text = 'next';
    break;
		
    default:
    return NULL;
  }

  if ($n_nid) {
    $n_node = node_load($n_nid);
		
    switch($n_node->type) {	
      case 'article': 
        $options = array('absolute' => TRUE);
        $nid = $n_node->nid;
        $url = url('node/' . $nid, $options);
        $html = '<a class="button" href="'. $url .'" />' . $n_node->title . '</a>'; 
      return $html; 
    }
  }
}

template.php

function pn_node($node, $mode = 'n') {
  if (!function_exists('prev_next_nid')) {
    return NULL;
  }

  switch($mode) {
    case 'p':
      $n_nid = prev_next_nid($node->nid, 'prev');
        $link_text = 'previous';
      break;
		
    case 'n':
      $n_nid = prev_next_nid($node->nid, 'next');
      $link_text = 'next';
    break;
		
    default:
    return NULL;
  }

  if ($n_nid) {
    $n_node = node_load($n_nid);
		
    switch($n_node->type) {	
      case 'article': 
        $html = l('"'.$n_node->title .'"', 'node/'.$n_node->nid); 
      return $html; 
    }
  }
}