PHP problem using database

$DB_HOST = "localhost";

$DB_USER = "root";

$DB_PASSWORD = "";

$DB_NAME = "practice";

$conn = new mysqli($DB_HOST,$DB_USER,$DB_PASSWORD,$DB_NAME);

if ($conn->connect_errno) {

printf("Connect failed: %s\n", $conn->connect_error);

exit();

}else{

//printf("connected!!!");

}

function NewUser() {

$fullname = $_POST['name'];

$userName = $_POST['user'];

$email = $_POST['email'];

$password = $_POST['pass'];

$query = "INSERT INTO websiteusers (fullname,userName,email,pass) VALUES ('$fullname','$userName','$email','$password')";

$data = $conn->query($query);

if($data) { <br>
    echo "YOUR REGISTRATION IS COMPLETED..."; <br>
}else{<br>
    echo "something wrong!!!";<br>
}<br>

}

function SignUp() {

if(!empty($_POST['user'])){

    $query1 = "SELECT userName,email";
    $data1 = $conn->query($query1);
    if($data1) { 
        NewUser(); 
        } else { 
            echo "SORRY...YOU ARE ALREADY REGISTERED USER..."; 
        } 
    } 

}

if(!isset($_POST['submit'])) {

$result = $conn->query("SELECT * FROM websiteusers");
while ($row = $result->fetch_assoc()) {
    printf ("%s (%s)\n", $row["userName"], $row["email"]);
}<br>
//SignUp(); 

}else{

SignUp();

}

?>

This is my PHP code for register but whenever i tried to register give me this error:

Notice: Undefined variable: conn in F:\Software\xampp\htdocs\LAB3\connectivity-sign-up.php on line 44

Fatal error: Call to a member function query() on null in

F:\Software\xampp\htdocs\LAB3\connectivity-sign-up.php on line 44 How to solve this problem? anyone please.