VBA Scheduling Algorithm in MS ACCESS - vba

Question

I want to calculate some schedules on the basis of given dates. Like I have
Start Date
End Date
Weekdays, for example, Monday, Wednesday as a frequency
and I need to calculate
weekly
biweekly
triweekly
monthly
quarterly
dates from the start and end date and also by matching the given weekdays.
For an example
Date start = 05/07/2018
Date End = 15/07/2018
Frequency days = Saturday
and I need weekly Saturday dates and then biweekly Saturday dates until it reaches to the end date.
I have tried DAYOFWEEK in MS ACCESS VBA which is helping a bit but I need to know the complete solution so I can calculate schedules.
Your help is appreciated.
Thanks

Answer 1

The DateAdd Function can do all that.
Air code:
d = StartDate
Do While d <= EndDate
Debug.Print d ' <-- Output date
Select Case Interval
Case "biweekly": d = DateAdd("ww", 2, d)
Case "monthly" : d = DateAdd("m", 1, d)
' etc.
End Select
Loop

Answer 2

For months, you should always add to the original startdate as this could be one of the last days of a month, thus is would offset the dates for months following a month having fewer days. So:
Dim StartDate As Date
Dim EndDate As Date
Dim NextDate As Date
Dim Interval As Long
StartDate = #1/31/2018#
EndDate = #6/30/2018#
Do
NextDate = DateAdd("m", Interval, StartDate)
Interval = Interval + 1
Debug.Print NextDate
Loop Until NextDate >= EndDate
will return:
2018-01-31
2018-02-28
2018-03-31
2018-04-30
2018-05-31
2018-06-30
For starting on a specific weekday, find the first of this, then add intervals as above:
Public Function DateNextWeekday( _
ByVal datDate As Date, _
Optional ByVal bytWeekday As Byte = vbMonday) _
As Date
' Returns the date of the next weekday, as spelled in vbXxxxday, following datDate.
' 2000-09-06. Cactus Data ApS.
' No special error handling.
On Error Resume Next
DateNextWeekday = DateAdd("d", 7 - (Weekday(datDate, bytWeekday) - 1), datDate)
End Function

Answer 3

This should work too - I have included input boxes so you can enter start date, finish date, day of the week and frequency because I don't know how you want that input; also this will store the values in a Table2 Which has a field/column called Dates and then you can retrieve them (I don't know either how do you want to retrieve the dates, if you want to store them etc.)...I hope this helps!:
Sub test()
'clear the table2:
CurrentDb.Execute "DELETE * FROM Table2"
Dim DBTest As String
Dim RSTest As DAO.Recordset
Dim i As Long
Dim selectorInitDate, selectorEndDate, DBDate As Date
'Enter Start Date
selectorInitDate = Format(InputBox("Initial Date"), "mm/dd/yyyy")
'Enter Finish Date
selectorEndDate = Format(InputBox("End Date"), "mm/dd/yyyy")
'Enter Day of the Week (example: Saturday)
selectorWeekDay = InputBox("Week Day")
'Enter Frecuency (example: weekly, biweekly, etc)
selectorFreqDays = InputBox("Frecuency Days")
If selectorWeekDay = "Sunday" Then WeekDaySelected = 1
If selectorWeekDay = "Monday" Then WeekDaySelected = 2
If selectorWeekDay = "Tuesday" Then WeekDaySelected = 3
If selectorWeekDay = "Wednesday" Then WeekDaySelected = 4
If selectorWeekDay = "Thursday" Then WeekDaySelected = 5
If selectorWeekDay = "Friday" Then WeekDaySelected = 6
If selectorWeekDay = "Saturday" Then WeekDaySelected = 7
If selectorFreqDays = "weekly" Then Freq = 7
If selectorFreqDays = "biweekly" Then Freq = 14
If selectorFreqDays = "triweekly" Then Freq = 21
If selectorFreqDays = "monthly" Then Freq = 30
If selectorFreqDays = "quarterly" Then Freq = 90
DBDate = Format(selectorInitDate, "mm/dd/yyyy")
Count = 0
Do While DBDate <= selectorEndDate
If Weekday(DBDate) = WeekDaySelected Then
DBTest = "INSERT INTO Table2 ([Dates]) " & _
" VALUES (" & _
"'" & DBDate & "');"
CurrentDb.Execute DBTest
DBDate = DBDate + Freq - 1
Count = Count + 1
End If
DBDate = DBDate + 1
Loop
'this retrieves in a msgbox the saturdays found between the two dates you specify:
DBTest = "SELECT * FROM Table2"
Set RSTest = CurrentDb.OpenRecordset(DBTest)
If Not RSTest.BOF And Not RSTest.EOF Then
RSTest.MoveFirst
Do While (Not RSTest.EOF)
If Format(RSTest.Fields("Dates").Value, "mm/dd/yyyy") >= selectorInitDate And _
Format(RSTest.Fields("Dates").Value, "mm/dd/yyyy") <= selectorEndDate Then
mthString = mthString & RSTest.Fields("Dates") & ", "
End If
RSTest.MoveNext
Loop
End If
' (remove last comma)
mthString = Left(mthString, Len(mthString) - 2)
MsgBox Count & " " & selectorWeekDay & "(s) Added" & Chr(43) & mthString
'clear the table2:
CurrentDb.Execute "DELETE * FROM Table2"
End Sub
Following your example this should give you how many saturdays you have between two dates in a weekly basis, and which are those dates.
Note: you need to have selected on your reference the "Microsoft DAO 3.6 Object Library"

Answer 4

If you just wanted the bi-weekly dates grouped in 14 day increments beginning with some starting date (first week of the year for example) indate could be the current date or some date you choose or you could just you today().
Function biweeklyDate(indate as date) as Date
biweeklyDate = (DateSerial(2021,1,4)-indate) Mod 14 + inDate
End function