Option Strict On

Public Class DiffForm

    Private Sub lblLoad_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles lblLoad.Click
        Dim filename1 As String = txtFileName1.Text
        Dim filename2 As String = txtFilename2.Text
        Dim listA() As String = loadArrayData(filename1)
        Dim listB() As String = loadArrayData(filename2)
        DisplayItemsNotInB(listA, listB)
        DisplayItemsNotInA(listA, listB)
    End Sub
    Sub DisplayItemsNotInB(ByVal a() As String, ByVal b() As String)
        Dim diff() As String = itemDiff(a, b)
        lstInANotB.Items.Clear()
        For i As Integer = 0 To diff.GetUpperBound(0)
            lstInANotB.Items.Add(diff(i))
        Next
    End Sub
    Sub DisplayItemsNotInA(ByVal a() As String, ByVal b() As String)
        Dim diff() As String = itemDiff(b, a)
        lstInBNotA.Items.Clear()
        For i As Integer = 0 To diff.GetUpperBound(0)
            lstInBNotA.Items.Add(diff(i))
        Next
    End Sub
    Function itemDiff(ByVal listA() As String, ByVal listB() As String) As String()
        Dim diff() As String = {"No Differences"}
        ' **** YOU NEED TO WRITE THIS FUNCTION 
        Return diff
    End Function
    Function loadArrayData(ByVal fname As String) As String()
        ' initialize the array where we will load the data into
        Dim myData(0) As String
        ' open the file

        Dim fh As IO.StreamReader
        Try
            fh = IO.File.OpenText(fname)
        Catch e As IO.FileNotFoundException
            Return mydata
        End Try
        ' keep track of the line number we are on (starting at 0)
        Dim line_num As Integer = 0
        ' loop until we hit the end of the file
        Do While fh.Peek <> -1
            ' make the array big enough
            ReDim Preserve myData(line_num)
            ' read a line from the data file and convert it to double and place in array
            myData(line_num) = fh.ReadLine
            ' increment the line number
            line_num += 1
        Loop
        fh.Close()
        ' return the newly constructed array
        Return myData
    End Function
End Class