How do I declare a two dimensional array?

You can also create an associative array, or a "hash-table" like array, by specifying the index of the array.

$array = array(
    0 => array(
        'name' => 'John Doe',
        'email' => '[email protected]'
    ),
    1 => array(
        'name' => 'Jane Doe',
        'email' => '[email protected]'
    ),
);

Which is equivalent to

$array = array();

$array[0] = array();
$array[0]['name'] = 'John Doe';
$array[0]['email'] = '[email protected]';

$array[1] = array();
$array[1]['name'] = 'Jane Doe';
$array[1]['email'] = '[email protected]';

The following are equivalent and result in a two dimensional array:

$array = array(
    array(0, 1, 2),
    array(3, 4, 5),
);

or

$array = array();

$array[] = array(0, 1, 2);
$array[] = array(3, 4, 5);

Just declare? You don't have to. Just make sure variable exists:

$d = array();

Arrays are resized dynamically, and attempt to write anything to non-exsistant element creates it (and creates entire array if needed)

$d[1][2] = 3;

This is valid for any number of dimensions without prior declarations.

Firstly, PHP doesn't have multi-dimensional arrays, it has arrays of arrays.

Secondly, you can write a function that will do it:

function declare($m, $n, $value = 0) {
  return array_fill(0, $m, array_fill(0, $n, $value));
}