How to Display Popular Posts by Views in WordPress without a Plugin

paste this below code into functions.php file

function getPostViews($postID){

    $count_key = 'post_views_count';

    $count = get_post_meta($postID, $count_key, true);

    if($count==''){

        delete_post_meta($postID, $count_key);

        add_post_meta($postID, $count_key, '1');

        return "1 জন পোষ্টটি দেখেছেন";

    }

    return $count.' জন পোষ্টটি দেখেছেন';

}

function setPostViews($postID) {

    $count_key = 'post_views_count';

    $count = get_post_meta($postID, $count_key, true);

    if($count==''){

        $count = 1;

        delete_post_meta($postID, $count_key);

        add_post_meta($postID, $count_key, '1');

    }else{

        $count++;

        update_post_meta($postID, $count_key, $count);

    }

}

Then add this where you want normally in post-sigle.php file 

<?php

          echo getPostViews(get_the_ID());

?>

and if you want to show the popular post list then add this where you want to show popular post list

<ul>
<?php
global $post;
$args = array( 'numberposts' => 5, 'offset'=> 1, 'category' => 1 );
$myposts = get_posts( $args );
foreach( $myposts as $post ) :  setup_postdata($post); ?>
<li><a href="<?php the_permalink(); ?>"><?php the_title(); ?></a></li>
    <li><?php setPostViews(get_the_ID()); echo getPostViews(get_the_ID());; ?></li>
<?php endforeach; ?>

Source: http://stackoverflow.com/questions/9472602/wordpress-popular-posts-without-using-plugins