Use this function to fix the missing protocol part from an URL

check_fix_url.php

<?php
function check_url($url) {
	if (substr($url, 0, 4) != 'http') {
		$url = 'http://'.$url;
	}
	$response = get_headers($url);
	if ($response[0] == 'HTTP/1.1 200 OK') {
		return $url;
	} elseif (in_array(substr($response[0], 9, 3), array(302, 301))) {
		foreach ($response as $r) {
			if (substr($r, 0, 8) == 'Location') {
				return str_replace('Location: ', '', $r);
				break;
			}
		}
	} elseif (substr($response[0], 9, 3) >= 400) {
		return '';
	}
}
echo check_url('www.finalwebsites.com');

I have customers or user which enter a website address without the protocol (http:// or https://).
Sure you can use some URL validation, but this function can fix it too.