Add x number of days to a date with vba in excel - date

Question

I am tring to add x number of days to a Long date with a pop up box.
Public Function AskForDeadlinePlus4() As String
Dim strUserResponse As String
strUserResponse = InputBox("Enter Validuntil Date: Add # of Days To Survey end date")
strUserResponse = FormatDateTime(strUserResponse + I2, vbLongDate)
ActiveSheet.Cells(2, 10).Value = strUserResponse 'the 2, 10 is the cell reference for J2 - row 2, column 10.
End Function
Where Survey end date in cell I2.
When I run this I get (Googling how to do this I am tiring)
4 + I2 (where I2 = Friday, April 05, 2013) >> Wednesday, January 03, 1900
of course I need Tuesday, April 09, 2013
Thanks

Answer 1

Have you used the DateAdd function?
Sub DateExample()
Dim strUserResponse As String '## capture the user input'
Dim myDate As Date '## the date you want to add to'
Dim numDays As Double '## The number of days you want to add'
strUserResponse = InputBox("Enter Validuntil Date: Add # of Days To Survey end date")
numDays = InputBox("How many days to add?")
myDate = CDate(strUserResponse)
MsgBox DateAdd("d", numDays, myDate)
End Sub

Answer 2

I think this code is what your after using the DateAdd(<base e.g. Day = "D">, <number>, <date>) function:
Public Function AskForDeadlinePlus4() As String
Dim strUserResponse As Date, iNumber As Long, rResponse As Variant
AskForDeadlinePlus4 = "" 'set default value
iNumber = CLng([I2])
rResponse = InputBox("Enter Validuntil Date: Add " & iNumber & " Day(s) To Survey end date")
If rResponse = False Then
'no value entered
Exit Function
ElseIf Not IsDate(rResponse) Then
'no date entered
Exit Function
Else
'valid date entered
strUserResponse = DateAdd("D", iNumber, CDate(rResponse))
End If
AskForDeadlinePlus4 = FormatDateTime(strUserResponse, vbLongDate)
End Function
Just a few points though:
The input function will return the Boolean FALSE if no input is entered.
The test you used above is a function and will return a value when used
If you want to use in in another VBA code, i = AskForDeadlinePlus4 is its usage;
But you can also use it in a cell but only when necessary as with every calculation this will prompt an input and for every cell its in, =AskForDeadlinePlus4; and
Plus I've added a check to see if a date was entered as the user may not enter a valid one.
If you want to use in VBA:
Sub GetInfo()
'the 2, 10 is the cell reference for J2 - row 2, column 10.
ActiveSheet.Cells(2, 10).Value = AskForDeadlinePlus4
End Sub

Answer 3

Instead of using DateAdd, which requires more typing, you could also use DateValue. Following would do it.
DateValue(strUserResponse )+I2
Another solution would be using the conversion function, CDate.
CDate(strUserResponse )+I2