You can use something really basic like this:
<?php
echo 'Current PHP version: ' . phpversion()
?>
Just add it into the (for example) index file and you'll see the current version.
mysql_* functions have been removed in PHP 7+.
You probably have PHP 7 in XAMPP. You now have two alternatives: MySQLi and PDO.
Additionally, here is a nice wiki page about PDO.
Best regards
Esskimo