Untitled

<?php
include ('login.php');

if (isset($_SESSION['login_user'])) {
header("location: index.php");
}
?>
<!DOCTYPE html>
<html>
   <head>
       <title>SV STAMA</title>
       <meta charset="UTF-8"/>

    <style type="text/css">
        //my stylesheet
    </style>
</head>
<body>
    <div class="login-page">
        <div class="form">
            <form class="register-form">
                <input type="text" placeholder="Voller Name" id="nameR" name="nameR"/>
                <input type="text" placeholder="Benutzername" id="usernameR" name="usernameR"/>
                <input type="text" placeholder="E-Mail" id="mailR" name="mailR"/>
                <input type="password" placeholder="Passwort" id="passwordR" name="passwordR"/>
                <input type="password" placeholder="Passwort wiederholen" id="passwordV" name="passwordV"/>
                <input type="number" placeholder="Klasse" min="5" max="13" step="1" id="classR" name="classR"/>
                <button name="register">Erstellen</button>
                <p class="message">
                    Bereits registriert? <a href="#">Einloggen</a>
                </p>
            </form>
            <form class="login-form" action="" method="post">
                <input type="text" placeholder="Benutzername" id="name" name="username"/>
                <input type="password" placeholder="Passwort" id="password" name="password"/>
                <button name="submit">Login</button>
                <p class="message">
                    Noch nicht registiert? <a href="#">Erstelle einen Account</a>
                </p>
            </form>
        </div>
    </div>
    <script type="text/javascript" src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.1.0/jquery.min.js"></script>
    <script src="script.js"></script>
</body>

<?php
session_start();
$error = '';
if (isset($_POST['submit'])) {
if (empty($_POST['username']) || empty($_POST['password'])) {
    $error = "Alle Felder ausfüllen!";
} else {
    $username = $_POST['username'];
    $password = $_POST['password'];
    $connection = mysql_connect("localhost", "***", "***") or die('Fehler: ' . mysql_error());
    $username = stripslashes($username);
    $password = stripslashes($password);
    $username = mysql_real_escape_string($username);
    $password = mysql_real_escape_string($password);
    $db = mysql_select_db("***") or die('Fehler: ' . mysql_error());
    $query = mysql_query("SELECT * FROM Benutzer WHERE username='$username'", $connection) or die('Fehler: ' . mysql_error());
    $rows = mysql_num_rows($query);
    $row = mysql_fetch_row($query);

    $pass = $row[4];

    if ($rows == 1) {
        if (password_verify($password, $pass)) {
            $_SESSION['login_user'] = $username;
            header("location: index.php");
        }
    } else {
        $error = "Username or Password is invalid";
    }
    mysql_close($connection);
}
}else if (isset($_POST['register'])) {
if (empty($_POST['nameR']) || empty($_POST['usernameR']) || empty($_POST['mailR']) || empty($_POST['passwordR']) || empty($_POST['passwordV']) || empty($_POST['classR'])) {
    $error = "Alle Felder ausfüllen!";
} else {
    $nameR = $_POST['nameR'];
    $usernameR = $_POST['usernameR'];
    $mailR = $_POST['mailR'];
    $passwordR = $_POST['passwordR'];
    $passwordV = $_POST['passwordV'];
    $classR = $_POST['classR'];

    if ($passwordV == $passwordR) {
        $connection = mysql_connect("localhost", "***", "***") or die('Fehler: ' . mysql_error());
        $db = mysql_select_db("***") or die('Fehler: ' . mysql_error());
        $query = mysql_query("SELECT * FROM Benutzer WHERE username='$usernameR'", $connection) or die('Fehler: ' . mysql_error());
        $rows = mysql_num_rows($query);

        if ($rows < 1) {
            $error = "Benutzername bereits vergeben!";
        } else {
            $insert_query = mysql_query("INSERT INTO Benutzer (username, name, klasse, password, e_mail) VALUES ('$usernameR','$nameR','$classR','$passwordR','$mailR')") or die('Fehler: ' . mysql_error());
            header("location:index.php");
        }
    } else {
        $error = "Passwörter stimmen nicht überein!";
    }
}
}
?>