How to implement a custom shortcode?

I’m trying to implement the shortcode found here. But when I put it into the functions.php of my theme it shows an error.

This is the coding for the shortcode:

function get_url($atts) {
 $pageURL = 'http';
 if ($_SERVER["HTTPS"] == "on") {$pageURL .= "s";}
 $pageURL .= "://";
 if ($_SERVER["SERVER_PORT"] != "80") {
  $pageURL .= $_SERVER["SERVER_NAME"].":".$_SERVER["SERVER_PORT"].$_SERVER["REQUEST_URI"];
 } else {
  $pageURL .= $_SERVER["SERVER_NAME"].$_SERVER["REQUEST_URI"];
 }
 return $pageURL;
}

function get_parenturl($atts) {
 $url = rtrim(get_url($atts),"/");
 $url = substr($url, 0, strrpos($url,"/"));
 if(strlen($url)>strlen("https://" + $_SERVER["SERVER_NAME"].":".$_SERVER["SERVER_PORT"]))
  return $url;
 else
  return "https://" + $_SERVER["SERVER_NAME"].":".$_SERVER["SERVER_PORT"];
}

add_shortcode('url', 'get_url');
add_shortcode('parentUrl', 'get_parenturl');

I’m also using the Frontier theme, if it matters.