<?php

$host = "localhost";
$db = "dev";
$user = "dev";
$pass = "dev";
$dsn = "mysql:host=$host;dbname=$db;";

try
{
    $pdo = new PDO($dsn, $user, $pass);
} catch (PDOException $ex) {
    echo 'Connection failed: ' . $ex->getMessage();
    die();
}

?>

<?php

include_once('pdo.inc.php');

class Customers
{
    function GetCustomerName($pdo, $customer_id)
    {
        $query = "SELECT first_name FROM Customers WHERE customer_id = :customer_id LIMIT 1";
        $stmt = $pdo->prepare($query);
        $stmt->bindParam(':customer_id', $customer_id);
        $stmt->execute();
        return $stmt->fetchColumn();
    }
}

?>

<?php

include_once('customers.class.php');

$a = new Customers();

echo $a->GetCustomerName($pdo, 1);

?>

function GetCustomerName(PDO $pdo, int $customer_id) {