<?php

class DB_Functions {

    private $db;

    function __construct() {

        require_once 'db_connect.php';

        $this->db = new DB_Connect();
        $this->db->connect();
    }

    public function getUser($uid, $password) {
        $result = mysql_query("SELECT * FROM users WHERE id = '$uid' AND pswd = '$password'") or die(mysql_error());

        $no_of_rows = mysql_num_rows($result);
        if ($no_of_rows > 0) {

            $result = mysql_fetch_array($result);
            return $result;

        } else {

            return false;
        }
    }

}

?>

<?php

class DB_Functions {

    private $db;

    function __construct() {

        require_once 'db_connect.php';

        $this->db = new DB_Connect();
        $this->db->connect();
    }

    public function getUser($uid, $password) {
        $stmt = $db->prepare("SELECT * FROM users WHERE id=? AND pswd=?");
        $stmt->execute(array($uid, $password));
        return $stmt->fetch();
    }

}

?>

require_once 'include/db_functions.php';
$db = new DB_Functions();


if ($tag == 'login') {

    $uid =mysql_real_escape_string($_POST['id']);
    $password =mysql_real_escape_string($_POST['pswd']);

    // check for user
    $user = $db->getUser($uid, $password);

    if ($user != false) {

        $response["success"] = 1;
        $response["user"]["id"] = $user["id"];

        echo json_encode($response);
    } else {

        $response["error"] = 1;
        $response["error_msg"] = "Incorrect email or password!";
        echo json_encode($response);
    }

if ($tag == 'login') {

    // check for user
    $user = $db->getUser( $_POST['id'], $_POST['pswd']);

    ... etc