my %months = (		## Change $ to %  and { to (   --- no reason to use a reference here.
         'JAN'  => '31',
         'FEB'  => "$feb",
         'MAR'  => '31',
         'APR'  => '30',
         'MAY'  => '31',
         'JUN'  => '30',
         'JUL'  => '31',
         'AUG'  => '31',
         'SEP'  => '30',
         'OCT' => '31',
         'NOV' => '30',
         'DEC' => '31',
        );				## Changed {  to )
  my @month_keys = (keys %months);
  my $tot_days = $dd;
  for (my $i = 0; $month_keys[$i] ne $mon; $i++) { # Added my