Неподдерживаемые типы операндов

Я работаю над функцией корзины для веб-сайта и наткнулся на эту ошибку:

Неустранимая ошибка: неподдерживаемые типы операндов в … в строке 77

Я думаю, это может быть потому, что я выполняю некоторую математику между переменной и значением внутри массива. Я не уверен в том, как выполнять математику по значению внутри массива:

($line_cost = $price * $quantity). 

Может ли кто-нибудь дать мне какое-либо руководство по этому поводу? Я буду очень благодарен! Вот мой код –

 <?php session_start(); ?> <?php $product_id = $_GET['id']; //the product id from the URL $action = $_GET['action']; //the action from the URL //if there is an product_id and that product_id doesn't exist display an error message if($product_id && !productExists($product_id)) { die("Error. Product Doesn't Exist"); } switch($action) { //decide what to do case "add": $_SESSION['cart'][$product_id]++; //add one to the quantity of the product with id $product_id break; case "remove": $_SESSION['cart'][$product_id]--; //remove one from the quantity of the product with id $product_id if($_SESSION['cart'][$product_id] == 0) unset($_SESSION['cart'][$product_id]); //if the quantity is zero, remove it completely (using the 'unset' function) - otherwise is will show zero, then -1, -2 etc when the user keeps removing items. break; case "empty": unset($_SESSION['cart']); //unset the whole cart, ie empty the cart. break; } ?> <?php if($_SESSION['cart']) { //if the cart isn't empty //show the cart echo "<table border=\"1\" padding=\"3\" width=\"40%\">"; //format the cart using a HTML table //iterate through the cart, the $product_id is the key and $quantity is the value foreach($_SESSION['cart'] as $product_id => $quantity) { //get the name, description and price from the database - this will depend on your database implementation. //use sprintf to make sure that $product_id is inserted into the query as a number - to prevent SQL injection $sql = sprintf("SELECT name, description, price FROM php_shop_products WHERE id = %d;", $product_id); $result = mysql_query($sql); //Only display the row if there is a product (though there should always be as we have already checked) if(mysql_num_rows($result) > 0) { list($name, $description, $price) = mysql_fetch_row($result); echo "$price"; var_dump($quantity); $line_cost = $price * $quantity; //work out the line cost $total = $total + $line_cost; //add to the total cost echo "<tr>"; //show this information in table cells echo "<td align=\"center\">$name</td>"; //along with a 'remove' link next to the quantity - which links to this page, but with an action of remove, and the id of the current product echo "<td align=\"center\">$quantity <a href=\"$_SERVER[PHP_SELF]?action=remove&id=$product_id\">X</a></td>"; echo "<td align=\"center\">$line_cost</td>"; echo "</tr>"; } } //show the total echo "<tr>"; echo "<td colspan=\"2\" align=\"right\">Total</td>"; echo "<td align=\"right\">$total</td>"; echo "</tr>"; //show the empty cart link - which links to this page, but with an action of empty. A simple bit of javascript in the onlick event of the link asks the user for confirmation echo "<tr>"; echo "<td colspan=\"3\" align=\"right\"><a href=\"$_SERVER[PHP_SELF]?action=empty\" onclick=\"return confirm('Are you sure?');\">Empty Cart</a></td>"; echo "</tr>"; echo "</table>"; }else{ //otherwise tell the user they have no items in their cart echo "You have no items in your shopping cart."; } //function to check if a product exists function productExists($product_id) { //use sprintf to make sure that $product_id is inserted into the query as a number - to prevent SQL injection $sql = sprintf("SELECT * FROM php_shop_products WHERE id = %d;", $product_id); return mysql_num_rows(mysql_query($sql)) > 0; } ?> <a href="products.php">Continue Shopping</a> <?php /* products table: CREATE TABLE `products` ( `id` INT NOT NULL AUTO_INCREMENT , `name` VARCHAR( 255 ) NOT NULL , `description` TEXT, `price` DOUBLE DEFAULT '0.00' NOT NULL , PRIMARY KEY ( `id` ) ); */ ?> </body> </html> с <?php session_start(); ?> <?php $product_id = $_GET['id']; //the product id from the URL $action = $_GET['action']; //the action from the URL //if there is an product_id and that product_id doesn't exist display an error message if($product_id && !productExists($product_id)) { die("Error. Product Doesn't Exist"); } switch($action) { //decide what to do case "add": $_SESSION['cart'][$product_id]++; //add one to the quantity of the product with id $product_id break; case "remove": $_SESSION['cart'][$product_id]--; //remove one from the quantity of the product with id $product_id if($_SESSION['cart'][$product_id] == 0) unset($_SESSION['cart'][$product_id]); //if the quantity is zero, remove it completely (using the 'unset' function) - otherwise is will show zero, then -1, -2 etc when the user keeps removing items. break; case "empty": unset($_SESSION['cart']); //unset the whole cart, ie empty the cart. break; } ?> <?php if($_SESSION['cart']) { //if the cart isn't empty //show the cart echo "<table border=\"1\" padding=\"3\" width=\"40%\">"; //format the cart using a HTML table //iterate through the cart, the $product_id is the key and $quantity is the value foreach($_SESSION['cart'] as $product_id => $quantity) { //get the name, description and price from the database - this will depend on your database implementation. //use sprintf to make sure that $product_id is inserted into the query as a number - to prevent SQL injection $sql = sprintf("SELECT name, description, price FROM php_shop_products WHERE id = %d;", $product_id); $result = mysql_query($sql); //Only display the row if there is a product (though there should always be as we have already checked) if(mysql_num_rows($result) > 0) { list($name, $description, $price) = mysql_fetch_row($result); echo "$price"; var_dump($quantity); $line_cost = $price * $quantity; //work out the line cost $total = $total + $line_cost; //add to the total cost echo "<tr>"; //show this information in table cells echo "<td align=\"center\">$name</td>"; //along with a 'remove' link next to the quantity - which links to this page, but with an action of remove, and the id of the current product echo "<td align=\"center\">$quantity <a href=\"$_SERVER[PHP_SELF]?action=remove&id=$product_id\">X</a></td>"; echo "<td align=\"center\">$line_cost</td>"; echo "</tr>"; } } //show the total echo "<tr>"; echo "<td colspan=\"2\" align=\"right\">Total</td>"; echo "<td align=\"right\">$total</td>"; echo "</tr>"; //show the empty cart link - which links to this page, but with an action of empty. A simple bit of javascript in the onlick event of the link asks the user for confirmation echo "<tr>"; echo "<td colspan=\"3\" align=\"right\"><a href=\"$_SERVER[PHP_SELF]?action=empty\" onclick=\"return confirm('Are you sure?');\">Empty Cart</a></td>"; echo "</tr>"; echo "</table>"; }else{ //otherwise tell the user they have no items in their cart echo "You have no items in your shopping cart."; } //function to check if a product exists function productExists($product_id) { //use sprintf to make sure that $product_id is inserted into the query as a number - to prevent SQL injection $sql = sprintf("SELECT * FROM php_shop_products WHERE id = %d;", $product_id); return mysql_num_rows(mysql_query($sql)) > 0; } ?> <a href="products.php">Continue Shopping</a> <?php /* products table: CREATE TABLE `products` ( `id` INT NOT NULL AUTO_INCREMENT , `name` VARCHAR( 255 ) NOT NULL , `description` TEXT, `price` DOUBLE DEFAULT '0.00' NOT NULL , PRIMARY KEY ( `id` ) ); */ ?> </body> </html> 

 $line_cost =(int)$price * (int)$quantity['key'];