VBA Runtime Error 9 (Excel 2007)

Question

i have got the following problem. I am creating an excel worksheet with active x elements to calculate several values (for a class in university). And in the following code i sometimes (not everytime) get the runtime error 9 that the index is out of range (hopefully i translated it correctly into english). I am new to vba. I know that there are several similar problems already asked but i have a huge problem to adapt the solutions to my code as i don't really understand either the problem in my code as also the solutions of their problems.

I marked the line for which the error occurs with stars.

I would be really thankful if anybody could explain, why this problem occurs in my code sometimes and how to solve it properly. Thank you in advance.

Here's the code:

Sub calcinull()
Dim ione(4), itwo(4), ii, ints(4), cs(4), io, it As Double
Dim a, b, c As Double

ione(0) = 0
ione(1) = 10
ione(2) = 20
ione(3) = 30
ione(4) = 40

itwo(0) = 100
itwo(1) = 90
itwo(2) = 80
itwo(3) = 70
itwo(4) = 60


For b = 0 To 4
    ii = ione(b) + (((itwo(b) - ione(b)) * (NPV(ione(b))) / (NPV(ione(b)) - NPV(itwo(b)))))
    ints(b) = ii
    cs(b) = NPV(ii)
Next b

Dim AbsInt(4), AbsCs(4) As Double

For a = 0 To 4
    AbsInt(a) = VBA.Abs(ints(a))
    AbsCs(a) = VBA.Abs(cs(a))
Next a

Dim pos As Integer

pos = Application.Match(Application.Min(AbsCs), AbsCs, 0)

*ii = ints(pos)*

If NPV(ii) > 0 Then
    io = ii
    If pos > 0 Then
        it = itwo(pos - 1)
    Else
        it = itwo(0)
    End If
ElseIf NPV(ii) < 0 Then
    it = ii
    If pos > 0 Then
        io = ione(pos - 1)
    Else
        io = ione(0)
    End If
ElseIf NPV(ii) = 0 Then
    inull = ii
End If

For c = 1 To 30
    Do Until (NPV(io) - NPV(it)) <> 0
        io = io - 0.1
        it = it + 0.1
    Loop
        ii = io + (((it - io) * (NPV(io)) / (NPV(io) - NPV(it))))
        If NPV(ii) > 0 Then
            io = ii
            If it > (io + 0.5) Then
                it = it - 0.5
            End If
        ElseIf NPV(ii) < 0 Then
            it = ii
            If io < (it - 0.5) Then
                io = io + 0.5
            End If
        ElseIf NPV(ii) = 0 Then
            inull = ii
            Exit For
        End If
Next c
inull = ii

End Sub

Answer 1

As ints is an array with 5 elements (0..4), probably pos is > 4 when this error occurs.

If you can't tell why, maybe put something like this behind the Match -Statement and set a breakpoint to the print while testing.

if pos < 0 or pos > 4 then
    debug.print pos & " is off"
end if

Answer 2

Alright guys, i solved it. The problem was, that the arrays uses indices from 0 to x, whereas the position gives the nth position of the array, which means, that my "pos"-variable is always one integer above the array-index.

Thank you all for your help!