Simple Zeller's congruence to get day of week

[TDarcos]

*** SPECIAL NOTICE *** I am editing this post on 9/16 to warn people reading this later that the Zeller's congruence formula I use below has an error. Whether that is because the formula was posted incorrectly or I copied it wrong, some dates it gets wrong, e.g. 12/31/2029, the program returns Tuesday, when the correct date is Monday. In any case, I accept sole responsibility for this error. Which means I did not change anything below, as owning one's mistakes means you don't hide them either.



I think this one is easier to understand than some of the others

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



Option _Explicit

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$(CheckDate, 2)): Minute = Val(Mid$(CheckDate, 4, 2)): Second = Val(Right$(CheckDate, 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

A copy is attached to this message.

Some points

1. Line 5 indicates I waive copyright on this file.
   
2. Line 43 allows you to select military time format by having a line earlier in the program with "$LET MILITARY=-1". or drop the $IF block and keep the one you want (or make it a regular IF statement if the user gets to choose).
   
3. The string functions around day and hour/minute/second are to make sure that day and hour don't have a trailing space, and so that minute and second have no leading or trailing spaces, but do have leading 0 if <10.