PHP | mysqli_close() Function

<?php
$servername = "localhost";
$username = "username";
$password = "password";

// Creating connection
$conn = mysqli_connect($servername, $username, $password);

// Checking connection
if (!$conn) {
    die("Connection failed: " . mysqli_connect_error());
}

// Creating a database named newDB
$sql = "CREATE DATABASE newDB";
if (mysqli_query($conn, $sql)) {
    echo "Database created successfully with the name newDB";
} else {
    echo "Error creating database: " . mysqli_error($conn);
}

// closing connection
mysqli_close($conn);

?>

<?php
$servername = "localhost";
$username = "username";
$password = "password";
$dbname = "newDB";

// checking connection
$conn = new mysqli($servername, $username, $password, $dbname);

// Check connection
if ($conn->connect_error) {
    die("Connection failed: " . $conn->connect_error);
}
//Close the connection
$conn->close();
?>

<?php
$servername = "localhost";
$username = "username";
$password = "password";

try {
    $conn = new PDO("mysql:host=$servername;dbname=newDB", 
                     $username, $password);

    // setting the PDO error mode to exception
    $conn->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);

    $sql = "CREATE DATABASE newDB";

    // using exec() because no results are returned
    $conn->exec($sql);

    echo "Database created successfully with the name newDB";
    }
catch(PDOException $e)
    {
    echo $sql . "
" . $e->getMessage();
    }
$conn = null;
?>