Trying to figure out how to delete item from cart in PHP - php

Question

I am trying to make an e-commerce website and I can't quite figure out how to get the cart to function. I am able to add amounts to the cart before purchase but I want it to delete the item from the cart when the quantity is set to 0.
if (isset($_POST['update'])) {
for ($i = 0; $i < sizeof($_SESSION['quantity']); $i++) {
$postID = 'qty' . $i;
$_SESSION['quantity'][$i] = $_POST[$postID];
if ($_SESSION['quantity'][$i] == 0) {
unset($_SESSION['shoppingcart'][$i]);
unset($_SESSION['quantity'][$i]);
unset($_SESSION['name'][$i]);
unset($_SESSION['price'][$i]);
}
}
}
Here is the cart variable that creates a table of all the products added
<form method="post">
<?php
if (!empty($_SESSION['shoppingcart'])) {
for ($i = 0; $i < sizeof($_SESSION['shoppingcart']); $i++) {
$cart .= '<tr>';
$cart .= '<td>' . $_SESSION['name'][$i] . '</td>';
$cart .= '<td><input type="text" id="quantity"name="qty' . $i . '"value="' . $_SESSION['quantity'][$i] . '" onkeyup="checkInput()"></td>';
$cart .= '<td>$' . $_SESSION['price'][$i] . '</td';
$cart .= '<td>$' . $_SESSION['quantity'][$i] * $_SESSION['price'][$i] . '</td>';
$cart .= '</tr>';
$total += ($_SESSION['quantity'][$i] * $_SESSION['price'][$i]);
$totalDiscounted += ($_SESSION['quantity'][$i] * $_SESSION['price'][$i]) / 100 * 30;
}
</form>
This works when I delete things going from the last piece in the array, going to the first thing added in the array in that order, but when I try to delete the first element or anything out of order first, it gives me an error. "Warning: Undefined array key 0". What am I doing wrong?

Answer 1

The undefined index come from the use of unset(). The indexes of the array will not be re-ordered after unset() call.
Exemple:
$array = [1, 2, 3];
unset($array[1]);
print_r($array); // indexes : 0 and 2.
You could:
use array_values() to re-index arrays.
unset($_SESSION['shoppingcart'][$i]);
$_SESSION['shoppingcart'] = array_values($_SESSION['shoppingcart']);
or, check the presence of the data in the loop :
for ($i = 0; $i < sizeof($_SESSION['shoppingcart']); $i++) {
if (!isset($_SESSION['name'][$i])) {
continue;
}
$cart .= '<tr>';
//...
}
Another way is to use a data structure for the order:
// add
$_SESSION['shoppingcart'][] = [
'quantity' => 1,
'name' => 'item',
'price' => 1.00,
];
// to update an index
$_SESSION['shoppingcart'][$index]['quantity'] = 2;
// to remove an index
unset($_SESSION['shoppingcart'][$index]);
then, use a foreach() to list
foreach ($_SESSION['shoppingcart'] => $data) {
// display item
}