Hulp voor login script

Hallo allemaal ik ben nieuw hier en ook met PHP redelijk noob.

Hier heb ik een script ik heb het gevonden op het internet maar ik heb het aangepast op my database gegevens en toch geeft het een fout. Ik wil graag weten wat ik fout doe of wat er fout aan is.

Fatal error: Call to undefined function mysql_select_database() in C:\xampp\htdocs\phplogin\register-exec.php on line 21

Dit is de fout melding en hieronder vind je de script

<?php
//Start session
session_start();

//Include database connection details
require_once('config.php');

//Array to store validation errors
$errmsg_arr = array();

//Validation error flag
$errflag = false;

//Connect to mysql server
$link = mysql_connect("localhost","root","");
if(!$link) {
die('Failed to connect to server: ' . mysql_error());
}

//Select database
mysql_select_database("loginsystem",$link);

//Function to sanitize values received from the form. Prevents SQL injection
function clean($str) {
$str = @trim($str);
if(get_magic_quotes_gpc()) {
$str = stripslashes($str);
}
return mysql_real_escape_string($str);
}

//Sanitize the POST values
$fname = clean($_POST['fname']);
$lname = clean($_POST['lname']);
$login = clean($_POST['login']);
$password = clean($_POST['password']);
$cpassword = clean($_POST['cpassword']);

//Input Validations
if($fname == '') {
$errmsg_arr[] = 'First name missing';
$errflag = true;
}
if($lname == '') {
$errmsg_arr[] = 'Last name missing';
$errflag = true;
}
if($login == '') {
$errmsg_arr[] = 'Login ID missing';
$errflag = true;
}
if($password == '') {
$errmsg_arr[] = 'Password missing';
$errflag = true;
}
if($cpassword == '') {
$errmsg_arr[] = 'Confirm password missing';
$errflag = true;
}
if( strcmp($password, $cpassword) != 0 ) {
$errmsg_arr[] = 'Passwords do not match';
$errflag = true;
}

//Check for duplicate login ID
if($login != '') {
$qry = "SELECT * FROM members WHERE login='$login'";
$result = mysql_query($qry);
if($result) {
if(mysql_num_rows($result) > 0) {
$errmsg_arr[] = 'Login ID already in use';
$errflag = true;
}
@mysql_free_result($result);
}
else {
die("Query failed");
}
}

//If there are input validations, redirect back to the registration form
if($errflag) {
$_SESSION['ERRMSG_ARR'] = $errmsg_arr;
session_write_close();
header("location: register-form.php");
exit();
}

//Create INSERT query
$qry = "INSERT INTO members(firstname, lastname, login, passwd) VALUES('$fname','$lname','$login','".md5($_POST['password'])."')";
$result = @mysql_query($qry);

//Check whether the query was successful or not
if($result) {
header("location: register-success.php");
exit();
}else {
die("Query failed");
}
?>

Ik heb geen flauw idee hoe ik het moet oplossen.

Mijn database naam is loginsystem

En dit is ook iets maar misschien kunnen jullie me uitleggen wat het doet ?

<?php
define('DB_HOST', 'localhost');
define('DB_USER', 'root');
define('DB_PASSWORD', '');
define('DB_DATABASE', 'test');
?>