How does this code to create an array in HTML accessed by PHP?

Question

I was going through Head First PHP and came by this piece of code.

<?php
    $dbc = mysqli_connect('localhost', 'root', 'atlantis2016', 'elvis_store')
        or die('Error connecting to MySQL server.');
    if(isset($_POST['submit']))
    {
      foreach ($_POST['todelete'] as $delete_id) 
      {
        $query = "DELETE FROM email_list WHERE id = $delete_id";
        mysqli_query($dbc, $query);
      }
      echo 'Customer removed. <br />';
    }

    $query = "SELECT * FROM email_list";
    $result = mysqli_query($dbc, $query);
    while ($row = mysqli_fetch_array($result)) 
    {
      echo '<input type="checkbox" value="' . $row['id'] . '" name="todelete[]" />';
      echo $row['first_name'];
      echo ' ' . $row['last_name'];
      echo ' ' . $row['email'];
      echo '<br />';
    }

    mysqli_close($dbc);
?>

I fully understand how we go through all the ids present in the array todelete by using the foreach loop.

What I don't get is how the array itself is created? Are there even arrays in HTML? IF not, how are we creating a PHP array using pure HTML in the following line?

echo '<input type="checkbox" value="' . $row['id'] . '" name="todelete[]" />';

Additionally, what I also find mysterious is how only those id's for which the checkboxes have been ticked end up in the array todelete while the others are ignored?

Basically, explain the origin and functioning of the todelete array for me, please.

This is an FAQ on the PHP site :) Check out: http://php.net/manual/en/faq.html.php#faq.html.arrays Let us know if you need clarifications. — ymas, Jul 13 '16 at 10:50
@ymas So let me get this right.. while todelete[] itself is not an array in HTML,but by the virtue of the `[]` after the name, the php script acting on it convert and creates an array called todelete. Is that correct? Also, why only certain values which are the ones of the checkboxes that have been ticked make its way into the todelete array? — Somenath Sinha, Jul 13 '16 at 10:56
Checkboxes aren't submitted as part of the request if they aren't checked, so only the ones that have been selected end up in the PHP array. And yes, you're correct on the first part. — iainn, Jul 13 '16 at 11:00

score 1 · Accepted Answer · edited May 23 '17 at 10:28

By defining the input name as todelete[], we are saying that this input variable todelete will send any selected checkboxes upon form submission to a PHP script by POST or GET.

The PHP script defined in the parent form 'action' attribute will be able to access values under $_REQUEST['todelete'] which will be an array structure.

This syntax is useful if we want to send multiple values associated to a variable name.

How does this code to create an array in HTML accessed by PHP?

2 Answers2