LogginForm

<!DOCTYPE html>
<html>
<head>
    <title>Loggin</title>
    <link rel="stylesheet" type="text/css" href="style.css">
</head>
<body>
    <div class="loggin">

        <form method="POST">
            <label for="user">User Name:</label>
            <input type="text" name="userName" id="user">
            <br>
            <label for="pass">Password:</label>
            <input type="password" name="password" id="pass">
            <br>
            <a href="Profile.php"><input type="submit" name="submit" value="Submit" /></a>
        </form>
        <form method="POST" action="Registration.php">
            <input type="submit" name="register" value="Register" />
        </form>
    </div>
    <?php

        $userName = trim($_POST['userName']);
        $userPass = trim($_POST['password']);
        $string = file_get_contents('data.txt');
        $string = explode("\n", $string);
        $error = true;
        foreach ($string as $key => $value) {
            $value = explode("!", $value);
                if (($userName === $value[0]) && ($userPass === $value[1])) {
                $error = false;
                break;
            }
        }
        if (empty($_POST['userName']) || empty($_POST['password'])) {
            echo "<p>You have to fill all fields!</p>";
        }
        if ($error) {
            echo "<p>Invalid username or password!</p>";
        }


        ?>
</body>
</html>