VBA: loop losing variable value - vba

Question

I've got a strange problem with a loop in VBA, as it seems to be losing the value of my variable. Any ideas why? If i delete the loop, debug.print shows "test", otherwise it's empty (unless I print the value of "dupa" inside the loop)... Seems very strange.
Function carbon_copy(indeks As String) As String
Dim emails(1 To 3) As String
Dim i As Integer
Dim dupa As String
emails(1) = "abc#wp.pl"
emails(2) = "pabc#wp.pl"
emails(3) = "rabc#wp.pl"
i = 1
dupa = "test"
Do While emails(i) <> ""
If i = indeks Then
GoTo NextIteration
End If
dupa = dupa & ";" & emails(i)
NextIteration:
i = i + 1
Loop
Debug.Print dupa
carbon_copy = dupa
End Function

Answer 1

You should get a runtime error 9 since you index i will be 4 after you looped through your emails String array. As soon as it tries to compare the value of emails(4) with "" it should produce the "index out of range" since you have defined your Array to be only 3 elements long.
For a little clarification try this example code, it should produce the same error:
Function littleTest()
Dim teststr(1 To 3) As String
Dim i As Integer
teststr(1) = "abc"
teststr(2) = "def"
teststr(3) = "ghi"
i = 1
Do While teststr(i) <> ""
Debug.Print "i do it for the " & i & " time!"
i = i + 1
Loop
End Function
You have already found the solution yourself since UBound() is returning the actual length of your array which is in your case three so it will never search beyond the array.

Answer 2

You're indexing out of the array bounds. The condition Do While emails(i) <> "" is always true given your array, so the this fails on emails(4). Just test the array bounds and loop over that:
For i = LBound(emails) To UBound(emails)
If emails(i) <> "" And i = indeks Then
dupa = dupa & ";" & emails(i)
End If
Next

Answer 3

Actually, I've already solved the problem by using other loop type (For i = 1 To UBound(emails), Next i), but why the previous loop did not work is still quite mysterious to me... If anyone can explain, I'd appreciate it, as I prefer to understand things rather thank just do them correctly.
W.

Answer 4

this should work (explanations in comments):
Function carbon_copy(indeks As Long) As String
Dim emails(1 To 3) As String
Dim i As Long
Dim dupa As String
emails(1) = "abc#wp.pl"
emails(2) = "pabc#wp.pl"
emails(3) = "rabc#wp.pl"
i = 1
Do While emails(i) <> ""
If i <> indeks Then dupa = dupa & ";" & emails(i) ' update 'dupa' if current index doesn't natch passed 'indeks'
i = i + 1
If i > UBound(emails, 1) Then Exit Do ' be sure to exit upon exceeding 'emails()' array size
Loop
carbon_copy = dupa
End Function