这个代码如何在PHP中访问HTML中创建数组？

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.

Answer 1

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.

See also: HTML input arrays