@thismonth = qw( $jandays $febdays $mardays $aprdays ...

# you obviously meant:
@thismonth = ($jandays,$febdays,$mardays,$aprdays, ...

##</code><code>##

my %days_in_month = (
   jan => 31,
   feb => 28,     # maybe?
   mar => 31,
   apr => 30,
   may => 31,
   etc ...
);