Problem using a VB6 OCX with a C#

Ah, so the IIf() function was evaluating all its arguments even when I equalled H which caused the X and Y arrays to exceed their bounds by one.

I'd always thought IIf() was a pseudo-function like C#'s ternary operator (?:) but it appears that (in VB6 at least) it works like a normal function. 

Anyway, makes perfect sense now, Rod :)

You are right Alan. The error was coming from the VB6 function. I modified it and everything worked like a charm. Your first suggestion worked well and so with the 2nd one. Thanks again. I appreciate it much. :)

The modified VB6 function:

Public Function AreaByCoords(ByRef X() As Double, ByRef Y() As Double) As Double
    Dim L As Long
    Dim H As Long
    Dim I As Integer
    Dim A As Double
   
    L = LBound(X)
    H = UBound(X)
    '
    If (H - L) < 3 Then Exit Function
    '
    A = 0
    For I = L To H
         If I = H Then
            A = A + Y(I) * X(L) - X(I) * Y(L)
         Else
             A = A + Y(I) * X(I + 1) - X(I) * Y(I + 1)
         End If
    Next I
    AreaByCoords = A / 2
End Function

That error is, presumably, bubbling up from the VB6 function though as both arrays have lengths of 4, it's difficult to see why :-/

My only other suggestion is to try making the two arrays entirely late-bound:

        Array C = Array.CreateInstance(typeof(double), 4);

        C.SetValue(1.542, 0);

        C.SetValue(2.285, 1);

        C.SetValue(-2.234, 2);

        C.SetValue(-2.521, 3);

      
        Array D = Array.CreateInstance(typeof(double), 4);

        D.SetValue(1.642, 0);

        D.SetValue(-2.585, 1);

        D.SetValue(-2.234, 2);

        D.SetValue(2.826, 3);

        V = axP1029.AreaByCoords (ref  C, ref D);
     

Hi Alan! Thank you for your suggestion. I tried it but I got a different error this time.

System.IndexOutOfRangeException {"Subscript out of range"}

How do I correct this? Thanks in advance.