get_comments_number

 * @since 1.5.0
 *
 * @param int|WP_Post $post_id Optional. Post ID or WP_Post object. Default is the global `$post`.
 * @return string|int If the post exists, a numeric string representing the number of comments
 *                    the post has, otherwise 0.
 */
function get_comments_number( $post_id = 0 ) {
	$post = get_post( $post_id );

	if ( ! $post ) {
		$count = 0;
	} else {
		$count   = $post->comment_count;
		$post_id = $post->ID;
	}

	/**
	 * Filters the returned comment count for a post.
	 *
	 * @since 1.5.0