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Even the formula and the algorithm that you posted has to have a reference
date to determine what a Sunday is (ie 0 = Sunday). There is a basic
argument in this thread, if you are looking for a day of the week there
must be somewhere in the course of calculation a starting point, the fact
that you can't see it doesn't mean it doesn't exist.
MarK A McCarty
AS/400 Programmer/Developer
Navy Exchange Service Command
quote for the day:
"Any person engaged in small business in America would be amazed looking at
this. Their jaws would drop at the money farmers receive."
- KEITH COLLINS, Agriculture Department economist, on government subsidies.
"Wills, Mike N.
(TC)" To: "'RPG400-L@midrange.com'"
<RPG400-L@midrange.com>
<MNWills@taylorco cc:
rp.com> Fax to:
Sent by: Subject: RE: Can I get the Day
of the week?
owner-rpg400-l@mi
drange.com
05/16/2001 10:41
AM
Please respond to
RPG400-L
There is a mathematical formula for getting the day of the week:
D = Day
M = Month
Y = the last two digits of the year
C = Century
((d + y) - (2 * c) + (y / 4) + (c / 4) + ((13 * m - 1) / 5)) % 7 = Day
For the Day: 0 = Sunday, 1 = Monday, etc.
For some reason my program is a day off right now but I am positive I had
it
working before. I haven't taken the time to debug it yet. This was done in
C++ on a PC. I need to double check my formula.
But with this formula it doesn't depend on a known date. I don't know if it
could cause problems, I just remember people keep on saying to NOT
hard-code
anything in if possible (although I am sure many of us do anyway). This is
a
formula that my instructor gave me and I have seen it on the web. Then, if
you (for some weird reason) need a day from the 1600's you can get it.
-----Original Message-----
From: DeLong, Eric [mailto:EDeLong@Sallybeauty.com]
Sent: Wednesday, May 16, 2001 8:51 AM
To: 'RPG400-L@midrange.com'
Subject: RE: Can I get the Day of the week?
No. I can't see that that's a problem. Personally, I can't see how one
could
determine the DOW without some sort of known date. These DOW functions are
both simple and effective. What's the problem?
Eric DeLong
-----Original Message-----
From: Wills, Mike N. (TC) [mailto:MNWills@taylorcorp.com]
Sent: Wednesday, May 16, 2001 8:30 AM
To: 'RPG400-L@midrange.com'
Subject: RE: Can I get the Day of the week?
The one problem I have with most of these suggestions is that the date is
then dependant upon a known date. Doesn't other people see something wrong
with this?
Mike
-----Original Message-----
From: boldt@ca.ibm.com [mailto:boldt@ca.ibm.com]
Sent: Wednesday, May 16, 2001 7:12 AM
To: rpg400-l@midrange.com
Subject: Re: Can I get the Day of the week?
From: "Christopher J. Devous" <cdevous@antigua.com>
Subject: RE: Can I get the Day of the week?
Christopher wrote:
>Try this, it's based on the famous "Doomsday" algorithm by JH Conway:
>
> 100
**************************************************************************
> 200 ***
> 300 *** Program Name -- DOWK
> 400 *** Description -- Calculate Day of Week from
Gregorian
> 500 *** Date
> 600 *** Author -- Christopher J. Devous
As much as I respect John Horton Conway, RPG programmers can't do
day of week computation much shorter than with this procedure:
//\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\//
// Procedure: DayOfWeek //
// Purpose: Determine the day of week for a particular date //
// Parameters: //
// I: dt -- date //
// Returns: //
// 0..6 -- 0=Sunday, 1=Monday, 2=Tuesday, etc. //
// Notes: //
// January 5, 1800 is a Sunday. This procedure only works for //
// dates later than 1800-01-05. //
//\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\//
P DayOfWeek b
D DayOfWeek pi 10i 0
D dt d value datfmt(*iso)
/free
return %rem (%diff (dt: d'1800-01-05': *days): 7);
/end-free
P DayOfWeek e
Hans Boldt, ILE RPG Development, IBM Toronto Lab, boldt@ca.ibm.com
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