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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??

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
4. the day should then be added
the reminder of 7 is the weekday starting with Sat==0

s\$\$([},&%#}/&/]+}%&{})*;#\$&&s&&\$^X.(\$'^"%]=\&(|?*{%
+.+=%;.#_}\&"^"-+%*).}%:##%}={~=~:.")&e&&s""`\$''`"e

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