PHP Multiple Checkboxes

Summary: in this tutorial, you will learn how to handle a form with multiple checkboxes in PHP.

How to handle multiple checkboxes on a form

A form may contain multiple checkboxes with the same name. When you submit the form, you’ll receive multiple values on the server under one name.

To get all the values from the checked checkboxes, you need to add the square brackets ([]) after the name of the checkboxes.

When PHP sees the square brackets ([]) in the field name, it’ll create an associative array of values where the key is the checkbox’s name and the values are the selected values.

The following example shows a form that consists of three checkboxes with the same name (colors[]) with different values "red", "green", and "blue".

<form action="index.php" method="post">
	<input type="checkbox" name="colors[]" value="red" id="color_red" />
	<label for="color_red">Red</label>

	<input type="checkbox" name="colors[]" value="green" id="color_green" />
	<label for="color_red">Green</label>

	<input type="checkbox" name="colors[]" value="blue" id="color_blue" />
	<label for="color_red">Blue</label>
        <input type="submit" value="Submit">
</form>Code language: HTML, XML (xml)

When you check three checkboxes and submit the form, the $_POST['colors'] will contain an array of three selected values:

array(3) 
{ 
    [0]=> string(3) "red" 
    [1]=> string(5) "green" 
    [2]=> string(4) "blue" 
}
Code language: plaintext (plaintext)

If you don’t check any checkboxes and submit the form, the $_POST array won’t have the colors key. And you can use the isset() function to check if the $_POST['colors'] is set:

isset($_POST['colors'])Code language: PHP (php)

Alternatively, you can use the filter_has_var() function:

filter_has_var(INPUT_POST, 'colors')Code language: PHP (php)

PHP multiple checkboxes example

We’ll create a simple app that allows users to order pizza toppings.

First, create the following file and directory structure:

.
├── css
│   └── style.css
├── img
│   └── pizza.svg
├── inc
│   ├── .htaccess
│   ├── footer.php
│   ├── functions.php
│   ├── get.php
│   ├── header.php
│   └── post.php
└── index.phpCode language: plaintext (plaintext)

File	Directory	Description
index.php	.	Contain the main logic that loads get.php or post.php depending on the HTTP request method
get.php	inc	Contain the code for showing a form with a checkbox when the HTTP request is GET.
post.php	inc	Contain the code for handling POST request
header.php	inc	Contain the code for the header
footer.php	inc	Contain the code for the footer
functions.php	inc	Contain the common functions
.htaccess	inc	Prevent direct access to the files in the inc directory
style.css	css	Contain the CSS code
pizza.svg	img	The pizza image that shows on the form

Second, add the following code to the header.php:

<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <link rel="preconnect" href="https://fonts.gstatic.com">
    <link href="https://fonts.googleapis.com/css2?family=Nanum+Gothic+Coding:wght@400;700&display=swap" rel="stylesheet">
    <link rel="stylesheet" href="css/style.css">
    <title>PHP Multiple Checkboxes - Pizza Toppings</title>
</head>

<body class="center">
    <main>
        <p><img src="img/pizza.svg" height="72" width="72" title="Pizza Toppings"></p>Code language: HTML, XML (xml)

Note that the page uses the Nanum Gothic Coding font. The header.php links to the style.css file. At the beginning of the body, it shows the pizza.svg image.

Third, add the following code to the footer.php:

</main>
</body>
</html>Code language: HTML, XML (xml)

The footer.php file contains the closing tags corresponding to the opening tags in the header.php file.

Fourth, define a function checked in the functions.php file:

<?php

function checked($needle, $haystack)
{
	if ($haystack) {
		return in_array($needle, $haystack) ? 'checked' : '';
	}

	return '';
}
Code language: PHP (php)

The checked() function returns the string 'checked' if the $need exists in the array $haystack or an empty string otherwise.

We’ll use this checked() function to refill the selected checkboxes on the form.

Fifth, add the following code to the index.php:

<?php

session_start();

require 'inc/header.php';

require 'inc/functions.php';

$pizza_toppings = [
	'pepperoni' => 0.5,
	'mushrooms' => 1,
	'onions' => 1.5,
	'sausage' => 2.5,
	'bacon' => 1.0,
];

$request_method = $_SERVER['REQUEST_METHOD'];

if ($request_method === 'GET') {
	require 'inc/get.php';
} elseif ($request_method === 'POST') {
	require 'inc/post.php';
}

require 'inc/footer.php';
Code language: PHP (php)

How the index.php works.

The index.php calls the session_start() function to start (or resume) a session. It loads the code from the header.php, functions.php, and footer.php.

The $pizza_toppings array stores the pizza toppings and prices. In a real application, you may get it from a database or an API.

If the HTTP method is GET, the index.php loads the form from the get.php file. In case the HTTP method is POST, it loads the code from the post.php file.

Sixth, create a form in the get.php file:

<form action="<?php echo htmlspecialchars($_SERVER['PHP_SELF']) ?>" method="post">

    <h1>Please select your pizza toppings:</h1>
    <ul>
        <?php foreach ($pizza_toppings as $topping => $price) : ?>
            <li>
                <div>
                    <input type="checkbox" name="pizza_toppings[]" value="<?php echo $topping ?>" id="pizza_topping_<?php echo $topping ?>" <?php echo checked($topping, $_SESSION['selected_toppings'] ?? []) ?> />
                    <label for="pizza_topping_<?php echo $topping ?>"><?php echo ucfirst($topping) ?></label>
                </div>
                <span><?php echo '$' . $price ?></span>
            </li>
        <?php endforeach ?>
    </ul>

    <button type="submit">Order Now</button>
</form>Code language: JavaScript (javascript)

The get.php file uses the $pizza_toppings array to dynamically generate checkboxes. The checked() function checks the checkbox if the value exists in the $_SESSION['selected_toppings'] variable.

When the page loads for the first time, the $_SESSION['selected_toppings'] is always empty. Later, we’ll add the selected values to it in the post.php.

Finally, place the code to handle form submission in the post.php file:

<?php

// sanitize the inputs
$selected_toppings = filter_input(
    INPUT_POST,
    'pizza_toppings',
    FILTER_SANITIZE_STRING,
    FILTER_REQUIRE_ARRAY
) ?? [];

// select the topping names
$toppings = array_keys($pizza_toppings);

$_SESSION['selected_toppings'] = []; // for storing selected toppings
$total = 0; // for storing total

// check data against the original values
if ($selected_toppings) {
    foreach ($selected_toppings as $topping) {
        if (in_array($topping, $toppings)) {
            $_SESSION['selected_toppings'][] = $topping;
            $total += $pizza_toppings[$topping];
        }
    }
} ?>
<?php if ($_SESSION['selected_toppings']) : ?>
    <h1>Order Summary</h1>
    <ul>
        <?php foreach ($_SESSION['selected_toppings'] as $topping) : ?>
            <li>
                <span><?php echo ucfirst($topping) ?></span>
                <span><?php echo '$' . $pizza_toppings[$topping] ?></span>
            </li>
        <?php endforeach ?>

        <li class="total"><span>Total</span><span><?php echo '$' . $total ?></span></li>
    </ul>
<?php else : ?>
    <p>You didn't select any pizza toppings.</p>
<?php endif ?>
<menu>
    <a class="btn" href="<?php htmlentities($_SERVER['PHP_SELF']) ?>" title="Back to the form">Change Toppings</a>
</menu>Code language: HTML, XML (xml)

The post.php file sanitizes the form input using the filter_input() function:

// sanitize the inputs
$selected_toppings = filter_input(
	INPUT_POST,
	'pizza_toppings',
	FILTER_SANITIZE_STRING,
	FILTER_REQUIRE_ARRAY
) ?? [];Code language: PHP (php)

It checks selected pizza toppings against the original values in the $pizza_toppings array and adds the selected values to the $_SESSION['selected_toppings'] variable. Also, it calculates the total price based on the selected pizza toppings.

$toppings = array_keys($pizza_toppings);

$_SESSION['selected_toppings'] = []; // for storing selected toppings
$total = 0; // for storing total

// check data against the original values
if ($selected_toppings) {
	foreach ($selected_toppings as $topping) {
		if (in_array($topping, $toppings)) {
			$_SESSION['selected_toppings'][] = $topping;
			$total += $pizza_toppings[$topping];
		}
	}
}Code language: PHP (php)

The markup part shows the order summary if one or more pizza toppings are selected.

Summary

Add square brackets ([]) at the end of the checkbox name when a form has multiple checkboxes with the same name.
PHP creates an associative array to stored values of the selected checkboxes if checkboxes have the same name that ends with [].

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