InputBox data validation and end loop - excel

Question

I have some code to enter dates via InputBox (see below). The problem is that the Else doesn't work (ie. if the user enters something other than the format mm/dd/yy it doesn't stop). How do I make it so that the user has to enter it in the format presented?
Also, I want to end the loop with the endDate. Right now, if you enter 01/10/20 as the start date and 12/31/20 as the end date, it will stop at January 1, 2021. How do I make it stop at December 31, 2020?
Dim startDate As Date
Dim endDate As Date
startDate = InputBox("Enter project start date in format mm/dd/yy", "User date", Format(Now(), "dd/mm/yy"))
endDate = InputBox("Enter project end date in format mm/dd/yy", "User date", Format(Now(), "dd/mm/yy"))
If IsDate(startDate) Then
startDate = Format(CDate(startDate), "mmm d, yyyy")
Else
MsgBox "Wrong date format"
End If
If IsDate(endDate) Then
endDate = Format(CDate(endDate), "mmm d, yyyy")
Else
MsgBox "Wrong date format"
End If
Range("A2").Value = startDate
Dim i As Long
Dim j As Long
Dim x As Integer
i = startDate
j = endDate
x = 3
Do Until i >= j
Cells(x, 1).Value = i + 7
i = i + 7
x = x + 1
Loop
End Sub```

Answer 1

When the date is incorrect it is displaying the message box but there is nothing to stop it from continuing through the code after the message box is closed. There are several ways you can fix this.
The first is to simply add the line
Exit Sub
after the msgbox is displayed.
However, I'm assuming you don't want the program to just give up after an incorrect input. Instead you likely want it to inform the user it was incorrect and ask for another input until they provide a valid format.
The way I typically do this is with a Do Until loop. Try this:
startDate = InputBox("Enter project start date in format mm/dd/yy", "User date",
Format(Now(), "dd/mm/yy"))
Do Until IsDate(startDate)
MsgBox "Wrong date format."
startDate = InputBox("Enter project start date in format mm/dd/yy", "User date",
Loop
endDate = InputBox("Enter project end date in format mm/dd/yy", "User date",
Format(Now(), "dd/mm/yy"))
Do Until IsDate(endDate)
MsgBox "Wrong date format."
startDate = InputBox("Enter project start date in format mm/dd/yy", "User date",
Loop
The second problem is because you are checking i's value before you add 7 to it. Plus, the endDate only gets printed if it happens to be a multiple of 7 away from the startDate. If you always want the end date to print you'll have to make some changes.
Try this instead:
i = startDate + 7
j = endDate
x = 3
Do Until i > j
Cells(x, 1).Value = i
i = i + 7
x = x + 1
Loop
Cells(x, 1).Value = endDate