How many days are in this month?

1. Given a function called day_of_month() that takes
   a UTC time value as input and returns a number from
   1 to 31 which represents the day of the month of the
   UTC passed in.

2. Given a variable called t in which the UTC value (number
   of seconds since January, 1, 1970, GMT) is stored
   for any date/time that falls within this month.

3. Given the fact that there are 86400 seconds in a day.

Days in this month =
32 - day_of_month((32 - day_of_month(t)) * 86400 + t)
                   ^------------------^
                             \____________ Number of days to add to
			                   the current day number to
					   ensure crossing over to
					   next month and always land
					   on the "32nd day" of this month.

PERL example:

#!/usr/bin/perl
$utc = time();

print "There are ".dim($utc)." days in this month.\n";

sub dom {
   my ($utc) = @_;
   my (@tp);
   @tp = localtime($utc);
   return $tp[3];
}

sub dim {
   my ($utc) = @_;
   return 32-dom((32-dom($utc))*86400+$utc);
}