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Re: Determining the dayname for the last day of any given month

by Skeeve (Vicar)
on Jun 19, 2006 at 21:23 UTC ( #556298=note: print w/replies, xml ) Need Help??

in reply to Determining the dayname for the last day of any given month

Another solution without using any module:
#!/usr/bin/perl -w use strict; while (1) { print "Enter year (yyyy) and month (mm), separated by a space:"; chomp(my $input = <STDIN>); last if !$input; my ($year, $month) = split / /, $input; my $m= $month % 12 + 1; my $y= $year+int($month/12); if ( $m<3) { $m+=12; --$y; } ++$m; my $dayname = (qw(Sat Sun Mon Tue Wed Thu Fri))[(int($m * 30.6) + +int($y * 365.25)-int($y / 100)+int($y / 400)) % 7]; print "The last day of $month/$year will be a $dayname\n"; }
The formular used here works like this:
  1. if the month is January or february (1 or 2) shift it to the end of the preceeding year (month 13 and 14)
  2. add 1 to the month
  3. sum up the integer result of:
    1. month * 30.6
      30.6 gives it the correct toggle between 30 and 31. February is the last month, so no problem with 28/29
    2. year * 365.25
      this takes into account the leap years
    3. year / -100
      this subtracts the non-leap years
    4. year / 400
      this re-adds the non-non-leap years
  4. the day should then be added
the reminder of 7 is the weekday starting with Sat==0


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