Simple Zeller's congruence to get day of week

[TDarcos]

I have fixed the program. The error about $SET MILITARYTIME=1 if you want to use that, was already in the program, and listed here, we were both wrong! I referred to it as $SET MILITARY=1 but you referred to it as $SET MILITARYTIM=1. I'm not nitpicking, I do appreciate how you found my error. Oh hell, I probably am nitpicking.

Speaking of nitpicking, I discovered a minor error. On line 42 of my original program, and line 39 of Steffan-68's corrected version (he drops some blank lines I used, that's a styling opinion), there should be a comma and space following the day, not just a space. That is also fixed, on line 47 of the revised version.

I also forgot to mention another feature of the program, which I'll mention after the listing.

Code: (Select All)

' Show-Date_and_Time.bas - Day of week computed using Zeller's congruence

' by Paul Robinson <paul@paul-robinson.us>

' September 15, 2024

' Dedicated to the Public Domain



' I'd like to thank user Steffan-68 from the QB64 Phoenix Edition Forums

' for his catching some errors I made

' September 16, 2024



Option _Explicit

Const Program_Version = "1.1" '  In case I have to fix it again...

Dim As String WeekDays(6), Months(12)

WeekDays(0) = "Saturday"

WeekDays(1) = "Sunday"

WeekDays(2) = "Monday"

WeekDays(3) = "Tuesday"

WeekDays(4) = "Wednesday"

WeekDays(5) = "Thursday"

WeekDays(6) = "Friday"

Months(1) = "January"

Months(2) = "February"

Months(3) = "March"

Months(4) = "April"

Months(5) = "May"

Months(6) = "June"

Months(7) = "July"

Months(8) = "August"

Months(9) = "September"

Months(10) = "October"

Months(11) = "November"

Months(12) = "December"



Dim As String CheckDate, CheckTime, AmPm

Dim As Integer Month, Day, Year, Hour, Minute, Second, WD

CheckDate = Date$

CheckTime = Time$

If CheckDate <> Date$ Then ' Midnight rolled over

    CheckDate = Date$

    CheckTime = Time$

End If

Month = Val(Left$(CheckDate, 2)): Day = Val(Mid$(CheckDate, 4, 2)): Year = Val(Right$(CheckDate, 4)):

Hour = Val(Left$(CheckTime, 2)): Minute = Val(Mid$(CheckTime, 4, 2)): Second = Val(Right$(CheckTime, 2))

WD = DayOfWeek(Month, Day, Year)



' Display date and time, formatted

Print "It is "; WeekDays(WD); ", "; Months(Month); Str$(Day); ","; Year; " at";

$If MILITARYTIME Then

    print checktime

$Else

    AmPm = " AM"

    If Hour > 12 Then

        AmPm = " PM"

        Hour = Hour - 12

    End If

    Print Str$(Hour); ":"; Right$("0" + LTrim$(Str$(Minute)), 2); ":"; Right$("0" + LTrim$(Str$(Second)), 2); AmPm

$End If



End





' Returns 0=Saturday, etc.

Function DayOfWeek% (Month%, Day%, Year%)

    Dim As Integer I, J, K, D, M, Y

    D = Day%: M = Month%: Y = Year%

    If M < 3 Then

        M = M + 12

        Y = Y - 1

    End If

    K = Y Mod 100

    J = Y / 100

    DayOfWeek = (D + 13 * (M + 1) / 5 + K + K / 4 + J / 4 + 5 * J) Mod 7

End Function

Now the one feature I forgot to mention is on lines 31-36 of my original, lines 29-34 of Stefan-68's correction, and on lines 36-41 of the revised version, you'll notice I reference DATE$ three times. The check of the date string against the current date, and then getting the date and time again if it changed, is a safety feature in the extremely rare, improbable case that it was exactly midnight when the time was captured, and the date just happened to change immediately after. I make sure I protect against any foreseeable error, 'improbable' is not the same as 'impossible,' and I always assume the universe will go after me or my creations at any chance it can get, and this eliminates that chance. 

I know, I calculated the speed of a date/time collection, about 30 years ago, and on a typical 4.77 mhz PC running interpreted Basic, it could collect over 2000 pairs in one second and a compiled Turbo Pascal program could do about 6,000, so statistically the probability is about once in 16 years. Today, with PCs over 800 times faster, the chance it could happen is extremely improbable. But again, improbable does not mean impossible.

If a program is using the Windows GetLocalTime function, however, it is atomic, both are collected simultaneously, so in that case it is impossible for the scenario to happen.