Get same nth day of the month in x number of months - vb.net

Question

I am needing some help converting a function from access vba to vb.net.
The script generates a new date, based on the date entered, and the number of months to be added.
“If today is the second Tuesday in March, what will be the second Tuesday in 4 months?”
Public Function NdNwk(dType As String, _
dtSpan As Integer, sDate As Date) As Variant
' This Function RETURNS the DAY of WHICH WEEK
' (e.g. Second Tuesday of the Month).
' FUNCTIONS to be passed to Variables:
' gtDoW: Day of the WEEK of the START DATE.
' (1 for Sunday, 2 for Monday, etc.)
' gtWoM: WEEK of the MONTH of the START DATE.
' (1 for First, 2 for Second, etc.)
' gtDSTdt: Desired DATE
' (generated by the [DateAdd] Function).
' CALL EXAMPLE: If TODAY is Tuesday, March 10, 2020,
‘ (second Tuesday of March), then using
' NdNwk(m, 2, #5/21/2020#)
' Would generate the DATE 5/12/2020,
' As the SECOND TUESDAY of MAY.
Dim gtDSTdt As Date, gtWoM As Integer, gtDoW As Integer
Dim iLoop As Integer, iPick As Integer, dstDTdom As Date
gtDoW = Weekday(sDate)
gtWoM = (Int((Day(sDate) - 1) / 7) + 1)
gtDSTdt = DateAdd(dType, dtSpan, sDate)
For iLoop = 1 To Day(DateSerial(Year(gtDSTdt), _
Month(gtDSTdt) + 1, 0))
dstDTdom = DateSerial(Year(gtDSTdt), _
Month(gtDSTdt), iLoop)
If Weekday(dstDTdom, 1) = gtDoW Then
iPick = iPick + 1
If iPick = gtWoM Then
NdNwk = dstDTdom
Exit Function
End If
End If
Next
End Function
Any and all help is appreciated here.

Answer 1

I used several of the properties and methods of the .net DateTime structure. https://learn.microsoft.com/en-us/dotnet/api/system.datetime?view=netcore-3.1
The arithmetic in the Function used the Mod operator which returns the remainder of the division. The integer division (the formard slash \) returns the integer portion of the division.
The only other thing that might be unfamiliar is the interpolated string, a string starting with $"". This allows you to directly embed variables in the string surround by { }.
Private Function NdNwk(InputDate As Date, MonthsAhead As Integer) As String
Dim newDate As Date
Dim DofWeek = InputDate.DayOfWeek
Dim Day = InputDate.Day
Dim OfInputMonth As Integer
If Day Mod 7 = 0 Then
OfInputMonth = Day \ 7
Else
OfInputMonth = (Day \ 7) + 1
End If
Dim TempDate = InputDate.AddMonths(MonthsAhead)
Dim NewMonth = TempDate.Month
Dim NewYear = TempDate.Year
Dim FirstWeek As Date
Dim NewDay As Integer
For d = 1 To 7
FirstWeek = New Date(TempDate.Year, TempDate.Month, d)
If FirstWeek.DayOfWeek = DofWeek Then
NewDay = d
Exit For
End If
Next
Dim DaysToAdd = (OfInputMonth - 1) * 7
newDate = New Date(NewYear, NewMonth, NewDay).AddDays(DaysToAdd)
Dim NewDateString = $"{newDate.ToString("MM/dd/yyyy")} is the {GetOrdinalString(OfInputMonth)} {DofWeek} of {TempDate.ToString("MMMM")}, {TempDate.Year}"
Return NewDateString
End Function
Private Function GetOrdinalString(input As Integer) As String
Dim output As String
Select Case input
Case 1
output = "1St"
Case 2
output = "2nd"
Case 3
output = "3rd"
Case 4
output = "4th"
Case 5
output = "5th"
Case Else
output = ""
End Select
Return output
End Function
Usage...
Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
Dim InputDate As Date
Dim MonthsToAdd As Integer
If Not Date.TryParse(TextBox1.Text, InputDate) Then
MessageBox.Show("Please enter a valid date in Date")
Return
End If
If Not Integer.TryParse(TextBox2.Text, MonthsToAdd) Then
MessageBox.Show("Please enter a valid number in Months To Add")
Return
End If
Dim d = NdNwk(InputDate, MonthsToAdd)
MessageBox.Show(d)
End Sub

Answer 2

First of all, thanks for all the feedback.
The solution that I was able to parse together is as follows:
A text box to show the number of months.
A text box to show the new date.
A button click action to run the following code:
Private Sub BtnMonth_Click(sender As Object, e As EventArgs) Handles BtnMonth.Click
Dim WrkDt As Date = Now
Dim QtyMnths As Integer = CType(TxtMntCount.Text, Int32)
Dim newFoM = New Date(WrkDt.Year, WrkDt.Month, 1).AddMonths(QtyMnths)
Dim DoWDt As Integer = WrkDt.DayOfWeek
Dim newMntdate = newFoM.AddDays(Enumerable.Range(0,
Date.DaysInMonth(newFoM.Year, newFoM.Month) - 1).Where(Function(i) newFoM.AddDays(i).DayOfWeek = DoWDt).Skip(1).First())
TxtNewDate.Text = Format(newMntdate, "MMMM dd, yyyy (ddd)")
End Sub
This works perfectly fine for me!
Mary's solution looks great, and I will give it a shot in the future when I need a modular input.
Thanks again for all the help!

Answer 3

I tested your solution, and it doesn’t produce the described results.
See test and correct solution at: https://dotnetfiddle.net/v5wGng
A couple of things from your original problem, you should prefer calculation to loops wherever possible, and you should use the required types wherever possible. If you have date in one format (string) and need it in another for your calculations, you should do the conversion and then call a function that does your calculations where all of the parameters are of the correct type.
Public Function GetSameWeekAndWeekDay(dt as date, months as integer) as Date
Dim newMonth =(new date(dt.year, dt.month, 1)).AddMonths(Months)
Dim week = getweek(dt)
Dim sameWeekDay = GetNthDayOfWeek(newMonth, week, dt.DayOfWeek)
Return SameWeekday
End Function
Public Function GetWeek(dt as date) as integer
Return(dt.day - 1) \ 7
End Function
Public Function GetNthDayOfWeek(dt as date, week as integer, weekDay as System.DayofWeek) as Date
Dim first = new Date(dt.year, dt.month, 1)
Dim baseDate = first.AddDays(-(first.DayOfWeek - system.dayofweek.Sunday))
Dim newDate = baseDate.AddDays((week * 7) + weekday)
If(newdate.DayOfWeek < first.DayOfWeek) then
newDate = newDate.AddDays(7)
End If
Return newdate
End Function