<?php
    
    error_reporting(-1);

    $data = array('foo' => '42', 'bar');
    echo $data['spinach'];
    echo $data[1];

    print_r($data);

Notice: Undefined index:  spinach in /t.php on line 6

Notice: Undefined offset:  1 in /t.php on line 7
Array
(
    [foo] => 42
    [0] => bar
)