Re: Can I get the Day of the week?

I see some hard coded values in your formula.  2, 4, 13 and 5 to be exact,
not counting the 7 your are dividing by to get the day of the week.

Not that I've unraveled this code, but my assumption is it's somehow converting
a date to a different format, perhaps even number of days since jan 1, 0001.
Which is a sunday.  Which is your base date.

It's just a different way to get the same thing we are doing, before there were
date values.

Hmm... yes.  Year / 4 (Leap year)  Century / 4 (Leap Year)   I can almost
decipher this code.  It is actually just counting the days from Jan 1st, not
positive if it's Jan 1, 0001 or Jan 1, 0000 though.

Regards,

Jim Langston

Me transmitte sursum, Caledoni!


"Wills, Mike N. (TC)" wrote:
> 
> 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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