Visual Basic

Public Class Form1 'The main form in the .EXE application
    ...
    Public obj As New iolibrary.LocalIO
    Declare Auto Function GetDataFromFile Lib "iolibrary.dll" (ByVal filename As String) As Array
    Declare Auto Function WriteDataToFile Lib "iolibrary.dll" (ByVal arraydata As Array, ByVal filename As String) As Integer

    [other functions/subs/events as required...]

    Private Sub cmdGetData_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles cmdGetData.Click
        'This sub makes a call to a function stored in a DLL (GetDataFromFile()) that
        'opens a predefined file (sFileName), gets data from it, stores that data in an
        'array, then returns the array for further processing.
        [data processing...]
        arInData = obj.GetDataFromFile(sInFileName)
        [data processing...]
    End Sub

    Private Sub cmdVendorToLocal_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles cmdVendorToLocal.Click
        'This function takes data stored in an array (arOutData), and passes it, along
        'with a predefined file name (sOutFileName) into a function stored in a DLL
        'which writes the data out to that file. It then returns the number of rows
        'written.
        [data processing...]
        iRecsWritten = obj.WriteDataToFile(arOutData, sOutFileName)
        [data processing...]
    End Sub
End Class

Public Class LocalIO
    Public Function GetDataFromFile(ByVal sFileName As String)
        [data processing...]
        Return arInData
    End Function

    Public Function WriteDataToFile(ByRef arData As Array, ByRef sOutFileName As String)
        [data processing...]
        Return iNumRecsWritten
    End Function
End Class