Note that ; $matrix[4][4]; only fills out the first level with five elements and populates the last with an array reference. This is because the last subscript doesn't do anything. Just like 

if ($foo[100000] == 1) {
    ...
}

[download]
doesn't extend @foo to be 100001 elements. This is also why it gives a "useless use of array element in void context" warning.

The first level is extended though, but only filled with undefs except for the fifth element which becomes an array reference, which will be empty because of the reason above, looking like 

[
    undef,
    undef,
    undef,
    undef,
    [ undef, undef, undef, undef , undef ],
]

[download]
Using the element in some way, not just using the value, like 
$matrix[4][4] = undef

[download]
would fill out the array reference at index four in the first level, but the other levels would still be untouched, so you'd have a "half-expanded" 2D array, looking like 
[
    undef,
    undef,
    undef,
    undef,
    [ undef, undef, undef, undef , undef ],
]

[download]
This is why Cody Pendant uses the for loop.

ihb

See perltoc if you don't know which perldoc to read!

In reply to Re^3: Initializing multidimensional arrays by ihb
in thread Initializing multidimensional arrays by pearle

Title:
Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post, it's "PerlMonks-approved HTML":


  • Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!
  • Titles consisting of a single word are discouraged, and in most cases are disallowed outright.
  • Read Where should I post X? if you're not absolutely sure you're posting in the right place.
  • Please read these before you post! —
  • Posts may use any of the Perl Monks Approved HTML tags:
    a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, details, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, summary, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr
  • You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)
            For:     Use:
    & &amp;
    < &lt;
    > &gt;
    [ &#91;
    ] &#93;
  • Link using PerlMonks shortcuts! What shortcuts can I use for linking?
  • See Writeup Formatting Tips and other pages linked from there for more info.