private $dbhost='localhost:3306';
private $dbuser='WebDes';
private $dbpass='1111';
private $dbname='db_lb4_32_2019';
private $mysqli_con;

private $pdo_con;
private $pdo_host='localhost';
private $pdo_port='3306';

/*подключение mysqli*/
public function connect() {
     $this->mysqli_con = new mysqli($this->dbhost, $this->dbuser, $this->dbpass, $this->dbname);
     $this->mysqli_con->query("SET CHARACTER SET 'utf8'");
}

/*подключение PDO
пример:
$dsn = "mysql:host=localhost;port=3306;dbname=solar_system;charset=utf8";
$options = [
      PDO::ATTR_ERRMODE => PDO::ERRMODE_EXCEPTION,
      PDO::ATTR_DEFAULT_FETCH_MODE => PDO::FETCH_ASSOC
    ];
$pdo = new PDO($dsn, 'testuser', 'testpassword', $options);
$pdo->query("SELECT * FROM dogovor");
*/
public function pdo_connect() {
    try {
        //точка "." в php это конкатенация(объединение) строк, если что
      $this->pdo_con = new PDO('mysql:host='.$this->pdo_host.';port='.$this->pdo_port.';dbname='.$this->dbname.'; charset=utf8', $this->dbuser, $this->dbpass, array(PDO::ATTR_ERRMODE => PDO::ERRMODE_EXCEPTION));
    } catch (PDOException $e) {
      echo 'unable to connect';
    }
}

/*пример запроса для mysqli*/
public function mysqli_query() {
    return $this->mysqli_com->query("SELECT * FROM dogovor");
}

/*пример запроса для PDO*/
public function pdo_query() {
    return $this->pdo_con->query("SELECT * FROM dogovor");
}