Week 4 FYP2 :

The error always appear when the data should be send to "localhost/mysql" by using XAMPP.  

Fatal error: Uncaught Error: Call to undefined function mysql_query() in C:\xampp\htdocs\Register\Login_code.php:10 Stack trace: #0 {main} thrown in C:\xampp\htdocs\Register\Login_code.php on line 10

$result = mysql_query($conn, $sql);

if(mysqli_num_rows($result) > 0)

The problem is mixing the mysql and mysqli in database we should choose either mysql extension or mysqli extension

I (improved)

because we are apply our database Application Programming Interface (API) the feature are allow in mysqli