Automatically Set the Featured Image in WordPress

post.php

<?php 
function wpforce_featured() {
          global $post;
          $already_has_thumb = has_post_thumbnail($post->ID);
              if (!$already_has_thumb)  {
              $attached_image = get_children( "post_parent=$post->ID&post_type=attachment&post_mime_type=image&numberposts=1" );
                          if ($attached_image) {
                                foreach ($attached_image as $attachment_id => $attachment) {
                                set_post_thumbnail($post->ID, $attachment_id);
                                }
                           }
                        }
      }  //end function
add_action('the_post', 'wpforce_featured');
add_action('save_post', 'wpforce_featured');
add_action('draft_to_publish', 'wpforce_featured');
add_action('new_to_publish', 'wpforce_featured');
add_action('pending_to_publish', 'wpforce_featured');
add_action('future_to_publish', 'wpforce_featured');
?>
<?php

function wpforce_featured() {
          global $post;
          $already_has_thumb = has_post_thumbnail($post->ID);
              if (!$already_has_thumb)  {
              $attached_image = get_children( "post_parent=$post->ID&post_type=attachment&post_mime_type=image&numberposts=1" );
                          if ($attached_image) {
                                foreach ($attached_image as $attachment_id => $attachment) {
                                set_post_thumbnail($post->ID, $attachment_id);
                                }
                           } else {
                                set_post_thumbnail($post->ID, '414');
                           }
                        }
      }  //end function
add_action('the_post', 'wpforce_featured');
add_action('save_post', 'wpforce_featured');
add_action('draft_to_publish', 'wpforce_featured');
add_action('new_to_publish', 'wpforce_featured');
add_action('pending_to_publish', 'wpforce_featured');
add_action('future_to_publish', 'wpforce_featured'); 
?>
<?php 
preg_match_all( '/<img .*?(?=src)src=\"([^\"]+)\"/si', get_the_content(), $allpics );
foreach($allpics[1] as $pics){
      echo $pics;
}

$post_details=get_post($post->ID);
preg_match_all( '/<img .*?(?=src)src=\"([^\"]+)\"/si', $post_details->post_content, $allpics );
foreach($allpics[1] as $pics){
    echo $pics;
}?>