%months = (
   Jan => [1,  '31'], Feb => [2,  ''  ], Mar => [3,  '31'],
   Apr => [4,  '30'], May => [5,  '31'], Jun => [6,  '30'],
   Jul => [7,  '31'], Aug => [8,  '31'], Sep => [9,  '30'],
   Oct => [10, '31'], Nov => [11, '30'], Dec => [12, '31']
);

# Get number of days in Jan
$days = $months{Jan}->[1];
   

##</code><code>##

# in numerical order
for ( sort { $a->[0] <=> $b->[0] } keys %months ) {

# or reversed
for ( sort { $b->[0] <=> $a->[0] } keys %months ) {