my @months = (undef, qw/Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec/);

##</code><code>##

    sub get_days {
        my ($mon) = @_;
        ...;
    }

##</code><code>##

    my @months = (
        undef,
        [ Jan => 31 ],
        [ Feb => 28 ],
        [ Mar => 31 ],
        [ Apr => 30 ],
        [ May => 31 ],
        [ Jun => 30 ],
        [ Jul => 31 ],
        [ Aug => 31 ],
        [ Sep => 30 ],
        [ Oct => 31 ],
        [ Nov => 30 ],
        [ Dec => 31 ],
    );