Can the first day of a century fall on a Sunday?

[Gösta H. Lovgren-2]

A programming challenge:

Answer here - http://www.straightdope.com/columns/...ll-on-a-sunday (No Peeking)

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"The follies which a man regrets the most in his life
are those which he didn't commit
when he had the opportunity."
-- Helen Rowland
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[Mel Bishop]

Running this Q-n-D program bears this out. Sunday along with Tuesday and Thursday. Interesting.

REM ********************************************************************
REM * AstroDay code function lifted from:                              *
REM * It finds the day of week the 1st of the month falls on           *
REM * http://www.powerbasic.com/support/forums/Forum4/HTML/003463.html *
REM * Author: Semen Matusovski                                         *
REM ********************************************************************
    DECLARE FUNCTION AstroDay(year AS LONG, _           '
                             month AS LONG, _           '
                             day   AS LONG) _           '
                                   AS LONG              '
                                                        '
FUNCTION PBMAIN                                         '
    LOCAL day, month, year AS LONG
    LOCAL t, col AS LONG
    LOCAL c0, c1, c2, c3, c4, c5, c6 AS LONG
                                                        '
    CONSOLE SCREEN 40,85                                '
    COLOR 14,1
    CLS

    LOCATE  3, 5 : PRINT;"   Sunday:";
    LOCATE  5, 5 : PRINT;"   Mondsy:";
    LOCATE  7, 5 : PRINT;"  Tuesday:";
    LOCATE  9, 5 : PRINT;"Wednesday:";
    LOCATE 11, 5 : PRINT;" Thursday:";
    LOCATE 13, 5 : PRINT;"   Friday:";
    LOCATE 15, 5 : PRINT;" Saturday:";

    f$ = "##,###"
    col = 16
    month = 1
    day = 1
    year = 0
    DO
    IF INKEY$ = CHR$(27) THEN EXIT LOOP
    year = year + 100
    LOCATE 1,5 : PRINT;year

    t = astroday(year, month, day) MOD 7
    IF t = 0 THEN INCR c0
    IF t = 1 THEN INCR c1
    IF t = 2 THEN INCR c2
    IF t = 3 THEN INCR c3
    IF t = 4 THEN INCR c4
    IF t = 5 THEN INCR c5
    IF t = 6 THEN INCR c6

    LOCATE  3,col : PRINT;c0
    LOCATE  5,col : PRINT;c1
    LOCATE  7,col : PRINT;c2
    LOCATE  9,col : PRINT;c3
    LOCATE 11,col : PRINT;c4
    LOCATE 13,col : PRINT;c5
    LOCATE 15,col : PRINT;c6

    LOOP
    WAITKEY$

                                                        '
    END FUNCTION                                        '
                                                        '
REM *****************************                       '
REM * What day of the week does *                       '
REM * the 1st fall on?          *                       '
REM *****************************                       '
                                                        '
FUNCTION AstroDay(year AS LONG, _                       '
                 month AS LONG, _                       '
                 day   AS LONG) AS LONG                 '
    DIM y AS DOUBLE                                     '
    y = year + (month - 2.85) / 12                      '
    AstroDay = INT(INT(INT(367 * y) - 1.75 * _          '
               INT(y) + day) -0.75 * _                  '
               INT(0.01 * y)) + 1721116                 '
    END FUNCTION                                        '

[Michael Mattias]

 LOCAL ST as SYSTEMTIME , FT AS FILETIME

  FOR YYYY =  1101 TO 9901  STEP 100  ' probably out of range
        ST.wYear = YYYY 
        ST.wMOnth  = 1
        ST.wDay     = 1 
        SystemTimeToFileTime  st, ft 
        FiletimeToSystemTime   ft, st    ' will return ST with day of week filled in 
        IF st.wDayOfWeek =  0 THEN    ' Sunday 
            ItCanHappen  = %TRUE 
            EXIT FOR
       END IF 
 NEXT

 If ISTRUE ItcanHappen THEN 
   ....

MCM

[Cliff Nichols]

Not sure the point unless prepping to prevent a Y3K problem?


Had to razz...but got the point

[Gösta H. Lovgren-2]

Well done Mel. Extra points for speed of reply (1 hour).

If ISTRUE ItcanHappen THEN ..MCM

Bravo. Cleverly done, Bro. (Points deducted for non-compileable untested code though)

PS, Had you peeked, the solution (MUCH more complicated/convoluted/longer/... than yours or Mel's) used 00's as first days of the centuries, not 01's. Wouldn't affect your solution though.

PSS, wouldn't the first century (AD) start at 0, not 1101, as well? (alas and alack ... more point deductions)

===================================
"The secret of (political) success
is honesty and fair dealing.
If you can fake those,
you've got it made."
Groucho Marx
===================================

[Mel Bishop]

PSS, wouldn't the first century (AD) start at 0, not 1101

No. Our current calendar jumped from 1 BC to 1 AD. There is no year zero.

Something I forgot when I wrote the program. However, like you noted, it doesn't matter. Same results calculating Sunday whether the starting year is zero or one.

[Michael Mattias]

I do "Big Ideas". Details are left to staff.

BTW, the snippet may be non-compileable, but it is NOT an untested technique. I do this all the time.

[Gösta H. Lovgren-2]

I do "Big Ideas". Details are left to staff.

BTW, the snippet may be non-compileable, but it is NOT an untested technique. I do this all the time.

Not to be "snippy", Mr. Big Head, but if it can't be run, it's untested, unless you are stating you have tested it and gotten results under conditions given. (As Mel did.) In which case I believe you.

[Paul Dixon]

Mel,
are you sure your code works? Leave it running for a minute and it appears that the first day of the year stops falling on any of the 7 weekdays!

Paul.

[Mel Bishop]

...are you sure your code works...

Well, after calculating several hundred thousand millenia into the future, it probably does fall short after a while.

[Gösta H. Lovgren-2]

Well, after calculating several hundred thousand millenia into the future, it probably does fall short after a while.

Maybe won't have weekdays in the future. And Mel just proved that.

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"While we are postponing,
life speeds by."
Seneca (3BC
65AD)
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