Using categories with the wp loop the manual way

gistfile1.php

<?php get_header();
/*
Template Name: Cats Grid Page
*/
?>


<p>Show the cats grid</p>
<div class="well"><ul>
  <?php 
    $categories = get_categories();
    foreach ($categories as $category) {
     echo  '<li><a href="?c='.$category->slug.'">'.$category->slug.'</a></li>';
    }
  ?>
</ul></div>
<hr>


<?php

// get only the cats that you get the c from the url
if(isset($_GET['c'])){
  $category = $_GET['c'];
  $args = array(
    'post_type' => 'cat',
    'category_name' => $category
  );
}
// get all them cats
else {
  $args = array(
    'post_type' => 'cat',
  );
}

$cats = new wp_query($args);

 if ($cats->have_posts()) : while ($cats->have_posts()) : $cats->the_post(); ?>

  	<h1><?php the_title(); ?></h1>
 	<?php the_content(); ?>


  <?php endwhile; else: ?>
    <p>Sorry, no pages matched your criteria.</p>
<?php endif; ?>


<?php get_footer(); ?>