PDO for循环问题

Question

I have a function that should calculate prices based on quantity.
The function should loop through every order and calculate every product price based on quantity, then should return order total price.
What i'm doing wrong?

public function getSumaComanda($cos) {
    $suma = $this->_db->query(sprintf("SELECT (@pretredus:=`pretredus`) AS `pretredus`,(CASE @pretredus WHEN 0 THEN `prettotal` ELSE `pretredus` END) AS `prettotal` , cantitate  FROM comenzi WHERE cos = '%d'", $cos));
    $suma->execute();
    $data_array = $suma->fetchAll(PDO::FETCH_ASSOC);

    $count = $this->_db->query(sprintf("SELECT COUNT(*) FROM cosuri WHERE id='%d'", $cos));
    $num = $count->fetchColumn();


    for ($x = 0; $x < $num; $x++) {
        $price = $data_array['cantitate'][$x] * $data_array['prettotal'][$x];
        $pret = $pret + $price;
        $pret = number_format($pret, 2, ".", "");

    }

    $rez = $pret;
    return $rez . ' Lei';
}

Answer 1

You should learn how to basically debug your variables. With using var_dump($data_array); you can see, what's in there.

You have to use the numerical index first:

$price = $data_array[$x]['cantitate'] * $data_array[$x]['prettotal'];

Nevertheless, your second query is useless. You don't have to count the results and can use instead a while-loop:

public function getSumaComanda($cos) {
    $suma = $this->_db->query(sprintf("SELECT (@pretredus:=`pretredus`) AS `pretredus`,(CASE @pretredus WHEN 0 THEN `prettotal` ELSE `pretredus` END) AS `prettotal` , cantitate  FROM comenzi WHERE cos = '%d'", $cos));
    $suma->execute();

    while ($data_array = $suma->fetch(PDO::FETCH_ASSOC)) {
        $pret += $data_array['cantitate'] * $data_array['prettotal'];
    }

    return number_format($pret, 2, ".", "") . ' Lei';
}