Adding values in an array

This works fine for me as well also:
Dim array1(0 To 100) As Double
Dim array2(0 To 100) As Double
Dim array3(0 To 100) As Double

array1(0) = 2
array1(1) = 5

array2(0) = 1
array2(1) = 6

array3(0) = array1(0) + array2(0)
array3(1) = array1(1) + array2(1)

Debug.Print array3(0) & vbCrLf & array3(1)

I will give this a try tomorrow...  
Thanks,
Ron

If upper bound for first array differs from the second:

Private Sub Command11_Click()
    Dim array1() As Double
    Dim array2() As Double
    Dim array3() As Double
   
    ReDim array1(3)
    ReDim array2(5)
    ReDim array3(5)
   
    Dim i As Integer
    For i = 0 To UBound(array1)
        array1(i) = i
        Debug.Print i
    Next
    For i = 0 To UBound(array2)
        array2(i) = i
        Debug.Print i
    Next
    If UBound(array1) >= UBound(array2) Then
        For i = 0 To UBound(array1)
            array3(i) = array1(i)
        Next
        For i = 0 To UBound(array2)
            array3(i) = array1(i) + array2(i)
        Next
    Else
        For i = 0 To UBound(array2)
            array3(i) = array2(i)
        Next

        For i = 0 To UBound(array1)
            array3(i) = array1(i) + array2(i)
        Next
    End If
    For i = 0 To UBound(array3)
        Debug.Print array3(i)
    Next
End Sub

Yeah...I put absolutely no error checking in my snippet; just assumed that all arrays were the same size and had the same lower/upper/bounds.

And now you run into the age old problem of storing derivable data.  There you are with a1, a2, and a3.  Someone changes a value in a1 or a2, but does not update a3 which is the sum - now what?  You have to make sure every time you view the contents of a3, it is in fact re-created.

Thank you very very much, particularly for the additional comments.