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Groups > comp.lang.c > #383384
| From | Peter 'Shaggy' Haywood <phaywood@alphalink.com.au> |
|---|---|
| Newsgroups | comp.lang.c |
| Subject | Re: getFirstDayOfMonth() |
| Date | 2024-03-05 14:03 +1100 |
| Organization | A noiseless patient Spider |
| Message-ID | <cleibk-jk1.ln1@hendrix.foo> (permalink) |
| References | <urrj5l$124o9$1@dont-email.me> <urssrf$1vntr$1@news.xmission.com> <uru0k6$1hpdi$1@dont-email.me> |
Groovy hepcat jak was jivin' in comp.lang.c on Sat, 2 Mar 2024 12:49 pm.
It's a cool scene! Dig it.
> Kenny McCormack ha scritto:
>> In article <urrj5l$124o9$1@dont-email.me>,
>> Mike Sanders <porkchop@invalid.foo> wrote:
>>> Just sharing what I've learned, hope some of you can adapt
>>> it for your own use.
>>>
>>> Calculates the name of the weekday (Sun, Mon, etc) for the
>>> 1st day of a given month & year...
>>>
>>> https://busybox.neocities.org/notes/get-first-day-of-month.txt
>>
>> Here's the guts of my version of the Zeller algorithm:
>>
>> int day(d,m,y)
>> int d, m, y;
>> {
>> if (m < 3) {
>> m += 12;
>> y--;
>> }
>> return (d + (13*m-27)/5 + y + y/4 - y/100 + y/400) % 7;
>
> Hi,
> I am referring in particular to this part of the equation:
> y + y/4 - y/100 + y/400
> Shouldn't it be calculated in a floating point and then truncated only
> the final result? Because, for example, if the year is 2024, the
> floating point calculation is 2514 (2514.82) while executed between
> integer is 2515.
No. The "+ y/4 - y/100 + y/400" part is adding a day for each leap
year. You see, a leap year is divisible by 4, but is not divisible by
100, but is divisible by 400. So, it's adding the number of years
divisible by 4, subtracting those divisible by 100 and adding those
divisible by 400 to determine the number of leap days up to the given
date.
So often in the last week or two I've heard people (who ought to know
better) on news programs on telly say that a leap year comes every 4
years, and I want to beat them about the head with a humorous object of
some kind until they get this right! A leap year does NOT come EVERY 4
years.
--
----- Dig the NEW and IMPROVED news sig!! -----
-------------- Shaggy was here! ---------------
Ain't I'm a dawg!!
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getFirstDayOfMonth() porkchop@invalid.foo (Mike Sanders) - 2024-03-01 03:48 +0000
Re: getFirstDayOfMonth() gazelle@shell.xmission.com (Kenny McCormack) - 2024-03-01 15:39 +0000
Re: getFirstDayOfMonth() Janis Papanagnou <janis_papanagnou+ng@hotmail.com> - 2024-03-01 17:12 +0100
Re: getFirstDayOfMonth() Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2024-03-01 08:28 -0800
Re: getFirstDayOfMonth() Janis Papanagnou <janis_papanagnou+ng@hotmail.com> - 2024-03-01 17:33 +0100
Re: getFirstDayOfMonth() Janis Papanagnou <janis_papanagnou+ng@hotmail.com> - 2024-03-01 17:37 +0100
Re: getFirstDayOfMonth() Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2024-03-01 10:34 -0800
Re: getFirstDayOfMonth() Janis Papanagnou <janis_papanagnou+ng@hotmail.com> - 2024-03-01 22:03 +0100
Re: getFirstDayOfMonth() porkchop@invalid.foo (Mike Sanders) - 2024-03-01 17:20 +0000
Re: getFirstDayOfMonth() scott@slp53.sl.home (Scott Lurndal) - 2024-03-01 16:47 +0000
Re: getFirstDayOfMonth() Janis Papanagnou <janis_papanagnou+ng@hotmail.com> - 2024-03-01 17:56 +0100
Re: getFirstDayOfMonth() porkchop@invalid.foo (Mike Sanders) - 2024-03-01 17:18 +0000
Re: getFirstDayOfMonth() porkchop@invalid.foo (Mike Sanders) - 2024-03-01 20:47 +0000
Re: getFirstDayOfMonth() scott@slp53.sl.home (Scott Lurndal) - 2024-03-01 21:38 +0000
Re: getFirstDayOfMonth() porkchop@invalid.foo (Mike Sanders) - 2024-03-01 21:50 +0000
Re: getFirstDayOfMonth() Tim Rentsch <tr.17687@z991.linuxsc.com> - 2024-03-03 09:52 -0800
Re: getFirstDayOfMonth() porkchop@invalid.foo (Mike Sanders) - 2024-03-02 00:00 +0000
Re: getFirstDayOfMonth() scott@slp53.sl.home (Scott Lurndal) - 2024-03-02 14:46 +0000
Re: getFirstDayOfMonth() Janis Papanagnou <janis_papanagnou+ng@hotmail.com> - 2024-03-02 16:41 +0100
Re: getFirstDayOfMonth() porkchop@invalid.foo (Mike Sanders) - 2024-03-02 19:59 +0000
Re: getFirstDayOfMonth() Janis Papanagnou <janis_papanagnou+ng@hotmail.com> - 2024-03-02 22:14 +0100
Re: getFirstDayOfMonth() porkchop@invalid.foo (Mike Sanders) - 2024-03-04 18:08 +0000
Re: getFirstDayOfMonth() Janis Papanagnou <janis_papanagnou+ng@hotmail.com> - 2024-03-05 03:03 +0100
Re: getFirstDayOfMonth() Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2024-03-02 14:22 -0800
Re: getFirstDayOfMonth() Janis Papanagnou <janis_papanagnou+ng@hotmail.com> - 2024-03-03 15:43 +0100
Re: getFirstDayOfMonth() David Brown <david.brown@hesbynett.no> - 2024-03-03 18:45 +0100
Re: getFirstDayOfMonth() Kaz Kylheku <433-929-6894@kylheku.com> - 2024-03-03 18:42 +0000
Re: getFirstDayOfMonth() David Brown <david.brown@hesbynett.no> - 2024-03-04 09:49 +0100
Re: getFirstDayOfMonth() Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2024-03-04 11:31 +0000
Re: getFirstDayOfMonth() Richard Harnden <richard.nospam@gmail.invalid> - 2024-03-04 14:23 +0000
Re: getFirstDayOfMonth() Janis Papanagnou <janis_papanagnou+ng@hotmail.com> - 2024-03-04 17:27 +0100
Re: getFirstDayOfMonth() porkchop@invalid.foo (Mike Sanders) - 2024-03-04 17:34 +0000
Re: getFirstDayOfMonth() scott@slp53.sl.home (Scott Lurndal) - 2024-03-04 17:40 +0000
Re: getFirstDayOfMonth() porkchop@invalid.foo (Mike Sanders) - 2024-03-04 18:11 +0000
Re: getFirstDayOfMonth() scott@slp53.sl.home (Scott Lurndal) - 2024-03-04 18:26 +0000
Re: getFirstDayOfMonth() Kaz Kylheku <433-929-6894@kylheku.com> - 2024-03-04 18:30 +0000
Re: getFirstDayOfMonth() scott@slp53.sl.home (Scott Lurndal) - 2024-03-04 19:01 +0000
Re: getFirstDayOfMonth() Janis Papanagnou <janis_papanagnou+ng@hotmail.com> - 2024-03-05 03:09 +0100
Re: getFirstDayOfMonth() scott@slp53.sl.home (Scott Lurndal) - 2024-03-05 15:06 +0000
Re: getFirstDayOfMonth() Janis Papanagnou <janis_papanagnou+ng@hotmail.com> - 2024-03-05 02:56 +0100
Re: getFirstDayOfMonth() porkchop@invalid.foo (Mike Sanders) - 2024-03-05 02:49 +0000
Re: getFirstDayOfMonth() Mark Bourne <nntp.mbourne@spamgourmet.com> - 2024-03-06 20:40 +0000
Re: getFirstDayOfMonth() scott@slp53.sl.home (Scott Lurndal) - 2024-03-06 20:54 +0000
Re: getFirstDayOfMonth() porkchop@invalid.foo (Mike Sanders) - 2024-03-04 17:26 +0000
Re: getFirstDayOfMonth() scott@slp53.sl.home (Scott Lurndal) - 2024-03-04 17:34 +0000
Re: getFirstDayOfMonth() Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2024-03-04 10:07 -0800
Re: getFirstDayOfMonth() porkchop@invalid.foo (Mike Sanders) - 2024-03-04 23:47 +0000
Re: getFirstDayOfMonth() Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2024-03-04 16:10 -0800
Re: getFirstDayOfMonth() porkchop@invalid.foo (Mike Sanders) - 2024-03-05 00:12 +0000
[OT] Re: getFirstDayOfMonth() Janis Papanagnou <janis_papanagnou+ng@hotmail.com> - 2024-03-05 03:18 +0100
Re: [OT] Re: getFirstDayOfMonth() porkchop@invalid.foo (Mike Sanders) - 2024-03-05 02:55 +0000
Re: getFirstDayOfMonth() scott@slp53.sl.home (Scott Lurndal) - 2024-03-05 15:03 +0000
Re: getFirstDayOfMonth() Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2024-03-05 13:25 -0800
Re: getFirstDayOfMonth() Lew Pitcher <lew.pitcher@digitalfreehold.ca> - 2024-03-04 21:21 +0000
Re: getFirstDayOfMonth() Michael S <already5chosen@yahoo.com> - 2024-03-05 00:37 +0200
Re: getFirstDayOfMonth() Michael S <already5chosen@yahoo.com> - 2024-03-05 11:41 +0200
Re: getFirstDayOfMonth() Tim Rentsch <tr.17687@z991.linuxsc.com> - 2024-03-14 15:57 -0700
Re: getFirstDayOfMonth() porkchop@invalid.foo (Mike Sanders) - 2024-03-04 23:35 +0000
Re: getFirstDayOfMonth() Janis Papanagnou <janis_papanagnou+ng@hotmail.com> - 2024-03-05 03:20 +0100
Re: getFirstDayOfMonth() James Kuyper <jameskuyper@alumni.caltech.edu> - 2024-03-03 04:06 -0500
Re: getFirstDayOfMonth() porkchop@invalid.foo (Mike Sanders) - 2024-03-04 18:21 +0000
Re: getFirstDayOfMonth() James Kuyper <jameskuyper@alumni.caltech.edu> - 2024-03-04 14:42 -0500
Re: getFirstDayOfMonth() Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2024-03-04 14:50 -0800
Re: getFirstDayOfMonth() porkchop@invalid.foo (Mike Sanders) - 2024-03-05 00:40 +0000
Re: getFirstDayOfMonth() Kaz Kylheku <433-929-6894@kylheku.com> - 2024-03-05 01:27 +0000
Re: getFirstDayOfMonth() porkchop@invalid.foo (Mike Sanders) - 2024-03-05 02:40 +0000
Re: getFirstDayOfMonth() scott@slp53.sl.home (Scott Lurndal) - 2024-03-05 15:05 +0000
Re: getFirstDayOfMonth() Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2024-03-04 17:39 -0800
Re: getFirstDayOfMonth() porkchop@invalid.foo (Mike Sanders) - 2024-03-05 02:43 +0000
Re: getFirstDayOfMonth() Michael S <already5chosen@yahoo.com> - 2024-03-05 01:08 +0200
Re: getFirstDayOfMonth() porkchop@invalid.foo (Mike Sanders) - 2024-03-05 00:18 +0000
Re: getFirstDayOfMonth() Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2024-03-04 16:33 -0800
Re: getFirstDayOfMonth() scott@slp53.sl.home (Scott Lurndal) - 2024-03-03 15:24 +0000
Re: getFirstDayOfMonth() Michael S <already5chosen@yahoo.com> - 2024-03-03 20:20 +0200
Re: getFirstDayOfMonth() scott@slp53.sl.home (Scott Lurndal) - 2024-03-03 18:56 +0000
Re: getFirstDayOfMonth() Mark Bourne <nntp.mbourne@spamgourmet.com> - 2024-03-03 13:17 +0000
Re: getFirstDayOfMonth() jak <nospam@please.ty> - 2024-03-02 02:49 +0100
Re: getFirstDayOfMonth() Tim Rentsch <tr.17687@z991.linuxsc.com> - 2024-03-03 09:47 -0800
Re: getFirstDayOfMonth() jak <nospam@please.ty> - 2024-03-04 02:26 +0100
Re: getFirstDayOfMonth() Peter 'Shaggy' Haywood <phaywood@alphalink.com.au> - 2024-03-05 14:03 +1100
Re: getFirstDayOfMonth() bart <bc@freeuk.com> - 2024-03-05 13:19 +0000
Re: getFirstDayOfMonth() jak <nospam@please.ty> - 2024-03-13 05:40 +0100
Re: getFirstDayOfMonth() jak <nospam@please.ty> - 2024-03-13 06:01 +0100
Re: getFirstDayOfMonth() Spiros Bousbouras <spibou@gmail.com> - 2024-03-13 13:38 +0000
Re: getFirstDayOfMonth() Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2024-03-13 08:47 -0700
Re: getFirstDayOfMonth() Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2024-03-13 09:11 -0700
Re: getFirstDayOfMonth() Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2024-03-13 07:36 -0700
Re: getFirstDayOfMonth() Tim Rentsch <tr.17687@z991.linuxsc.com> - 2024-03-14 19:56 -0700
Re: getFirstDayOfMonth() Kaz Kylheku <433-929-6894@kylheku.com> - 2024-03-02 03:44 +0000
Re: getFirstDayOfMonth() Peter 'Shaggy' Haywood <phaywood@alphalink.com.au> - 2024-03-05 14:07 +1100
Re: getFirstDayOfMonth() gazelle@shell.xmission.com (Kenny McCormack) - 2024-03-05 13:30 +0000
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