致命错误: Uncaught :不支持操作数类型: string * string

Question

以下是完整的错误：

致命错误: Uncaught :不支持的操作数类型: C:\xampp\htdocs\HomemadeNepal\purchase.php:22堆栈跟踪中的string * string：#0 {main}抛出在第22行的C:\xampp\htdocs\HomemadeNepal\purchase.php中

以下是代码：

<?php
include('conn.php');
if (isset($_POST['productid'])) {

    $customer = $_POST['customer'];
    $number = $_POST['number'];
    $sql = "insert into purchase (customer,number, date_purchase) values ('$customer','$number', NOW())";
    $conn->query($sql);
    $pid = $conn->insert_id;

    $total = 0;

    foreach ($_POST['productid'] as $product) :
        $proinfo = explode("||", $product);
        $productid = $proinfo[0];
        $iterate = $proinfo[1];
        $sql = "select * from product where productid='$productid'";
        $query = $conn->query($sql);
        $row = $query->fetch_array();

        if (isset($_POST['quantity' . $iterate])) {
            $subt = $row['price'] * $_POST['quantity' . $iterate]; <!--THIS IS THE LINE 22 WITH THE ERROR)
            $total += $subt;

            $sql = "insert into purchase_detail (purchaseid, productid, quantity) values ('$pid', '$productid', '" . $_POST['quantity' . $iterate] . "')";
            $conn->query($sql);
        }
    endforeach;

    $sql = "update purchase set total='$total' where purchaseid='$pid'";
    $conn->query($sql);
    header('location:Thankyou.php');
} else {
?>
    <script>
        window.alert('Please select a product');
        window.location.href = 'order.php';
    </script>
<?php
}
?>

Answer 1

$row['price']和$_POST['quantity' . $iterate]返回不能乘以的字符串。因此，您必须将这两个值转换为int值：

$subt = (int)$row['price']* (int)$_POST['quantity' . $iterate]

Answer 2

您可以使用intval()函数

$subt = (intval)$row['price'] * (intval)$_POST['quantity' . $iterate]