How to add url parameter to the current url?

There is no way to write a relative URI that preserves the existing query string while adding additional parameters to it.

You have to:

topic.php?id=14&like=like

function currentUrl() {
    $protocol = strpos(strtolower($_SERVER['SERVER_PROTOCOL']),'https') === FALSE ? 'http' : 'https';
    $host     = $_SERVER['HTTP_HOST'];
    $script   = $_SERVER['SCRIPT_NAME'];
    $params   = $_SERVER['QUERY_STRING'];

    return $protocol . '://' . $host . $script . '?' . $params;
}

Then add your value with something like;

echo currentUrl().'&value=myVal';