Day of the week
A company decides that whenever Xmas falls on a Sunday that they will give their workers all extra paid holidays so that, together with any public holidays, workers will not have to work the following week (between the 25th of December and the first of January).
You are encouraged to solve this task according to the task description, using any language you may know.
In what years between 2008 and 2099 will the 25th of December be a Sunday?
Using any standard date handling libraries of your programming language; compare the dates calculated with the output of other languages to discover any anomalies in the handling of dates which may be due to, for example, overflow in types used to represent dates/times similar to yp:Y2k#See_also y2k problems.
Java
<java>import java.util.Calendar; import java.util.Date; import java.util.GregorianCalendar;
public class Blah { public static void main(String[] args) { for(int i = 2008;i<=2099;i++){ GregorianCalendar cal = new GregorianCalendar(i, Calendar.DECEMBER, 25); if((cal.get(Calendar.DAY_OF_WEEK))==Calendar.SUNDAY){ System.out.println(new Date(cal.getTimeInMillis())); } } } }</java> Output:
Sun Dec 25 00:00:00 CST 2011 Sun Dec 25 00:00:00 CST 2016 Sun Dec 25 00:00:00 CST 2022 Sun Dec 25 00:00:00 CST 2033 Sun Dec 25 00:00:00 CST 2039 Sun Dec 25 00:00:00 CST 2044 Sun Dec 25 00:00:00 CST 2050 Sun Dec 25 00:00:00 CST 2061 Sun Dec 25 00:00:00 CST 2067 Sun Dec 25 00:00:00 CST 2072 Sun Dec 25 00:00:00 CST 2078 Sun Dec 25 00:00:00 CST 2089 Sun Dec 25 00:00:00 CST 2095
UNIX Shell
#! /bin/bash for((i=2009; i <= 2099; i++)) do date -d "$i-12-25" |grep Sun done exit 0
The first lines of output are
Sun Dec 25 00:00:00 CET 2011 Sun Dec 25 00:00:00 CET 2016 Sun Dec 25 00:00:00 CET 2022 Sun Dec 25 00:00:00 CET 2033 date: invalid date `2038-12-25'
I.e., starting from year 2038, the date command (which uses the glibc library, at least on GNU systems), is not able to recognise the date as a valid one!
Different machine/OS version #1
This is the same command run on RedHat Linux.
bash-3.00$ date --version date (coreutils) 5.2.1 Written by David MacKenzie. Copyright (C) 2004 Free Software Foundation, Inc. This is free software; see the source for copying conditions. There is NO warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. bash-3.00$ uname -a Linux brslln01 2.6.9-67.ELsmp #1 SMP Wed Nov 7 13:56:44 EST 2007 x86_64 x86_64 x86_64 GNU/Linux bash-3.00$ for((i=2009; i <= 2099; i++)); do date -d "$i-12-25" |egrep Sun; done Sun Dec 25 00:00:00 GMT 2011 Sun Dec 25 00:00:00 GMT 2016 Sun Dec 25 00:00:00 GMT 2022 Sun Dec 25 00:00:00 GMT 2033 Sun Dec 25 00:00:00 GMT 2039 Sun Dec 25 00:00:00 GMT 2044 Sun Dec 25 00:00:00 GMT 2050 Sun Dec 25 00:00:00 GMT 2061 Sun Dec 25 00:00:00 GMT 2067 Sun Dec 25 00:00:00 GMT 2072 Sun Dec 25 00:00:00 GMT 2078 Sun Dec 25 00:00:00 GMT 2089 Sun Dec 25 00:00:00 GMT 2095 bash-3.00$