Why does the date returns “31-12-1899” when 1 is passed to it?

Question

I am using windows 10 OS excel 13 so in the below code 1 should return 1/1/1900 right ? below it doesn\'t why.

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Answer 1

Integers and dates map differently in VBA than in the worksheet. For example:

Sub marine()
    Dim i As Integer, d As Date
    Dim mgs As String

    msg = ""
    For i = -10 To 10
        d = CDate(i)
        msg = msg & i & vbTab & Format(d, "mm/dd/yyyy") & vbCrLf
    Next i

    MsgBox msg
End Sub

Produces:

Note you can get dates prior to 1/1/1900

EDIT#1:

This may help to understand the difference. I put some integers in column A.

In B1, I put =A1 and copy down. I format column B to display in date format.

I use this UDF():

Public Function VBA_Date(i As Long) As String
    VBA_Date = Format(CDate(i), "mm/dd/yyyy")
End Function

To fill column C:

Note the transition between rows #19 and #20