THIS CODE GOES IN THE TRANSACTION.VB MODULE ----------------------------------------------------------

Public Function CalcEffectOfTransactionOnMargin(targdate As Date) As Double
        ' The code (version 2) is provided to you as a link from the homework.
        ' Make sure that you understand the financial logic.
        ' This function calculates the effect of the current transaction on your overall margin

        Select Case type
            Case "Sell"
                '  Sell has no effect on margin because you can only sell what you have long
                Return 0 ' effect of transaction on margin

            Case "Buy"
                If currentPositionInAP >= 0 Then
                    Return 0
                Else
                    If qty >= Math.Abs(currentPositionInAP) Then
                        Return -currentPositionInAP * mtm
                        ' buying eliminates all margin for this symbol
                    Else
                        Return (qty * mtm)
                        ' buying reduces the margin
                    End If
                End If

            Case "SellShort"
                Return -qty * mtm
                ' Selling short is easy: it always increases the margin

            Case "CashDiv"
                Return 0

            Case "X-Call"
                ' Two effects on margin: the change in options and the change in stocks
                Dim OptionEffect As Double = 0
                underlierCurrentPositionInAP = GetCurrentPositionInAP(underlier)

                ' first the effect of exercising the call on the call position
                If currentPositionInAP < 0 Then
                    OptionEffect = qty * mtm
                    ' i.e., it reduces the margin
                Else
                    OptionEffect = 0
                End If

                ' next, the effect of the called stock
                ' two cases: long and short calls.
                If currentPositionInAP >= 0 Then      ' long call is like buying
                    If underlierCurrentPositionInAP >= 0 Then
                        Return OptionEffect
                    Else
                        If qty >= Math.Abs(underlierCurrentPositionInAP) Then
                            Return OptionEffect - (underlierCurrentPositionInAP * mtmUnderlier)
                            ' X-call eliminates all margin for this symbol
                        Else
                            Return OptionEffect + (qty * mtmUnderlier)
                            ' X-call reduces the margin
                        End If
                    End If

                Else      '  exercising short calls is like selling

                    If underlierCurrentPositionInAP <= 0 Then
                        Return OptionEffect - (qty * mtmUnderlier)
                    Else   ' underlier positive
                        If underlierCurrentPositionInAP >= qty Then
                            Return OptionEffect
                        Else
                            Return OptionEffect - ((qty - underlierCurrentPositionInAP) * (qty * mtmUnderlier))
                        End If
                    End If
                End If

            Case "X-Put"
                ' Two effects on margin: the change in options and the change in stocks
                Dim OptionEffect As Double = 0
                underlierCurrentPositionInAP = GetCurrentPositionInAP(underlier)

                ' first the effect of exercising the option on the put position
                If currentPositionInAP < 0 Then
                    OptionEffect = qty * mtm
                    ' and it reduces the margin
                Else
                    OptionEffect = 0
                End If

                ' next, the effect of the stock
                ' two cases: long and short puts
                If currentPositionInAP < 0 Then      ' short put is like buying

                    If underlierCurrentPositionInAP >= 0 Then
                        Return OptionEffect
                    Else
                        If qty >= Math.Abs(underlierCurrentPositionInAP) Then
                            Return OptionEffect - (underlierCurrentPositionInAP * mtmUnderlier)
                            ' X-put eliminates all margin for this symbol
                        Else
                            Return OptionEffect + (qty * mtmUnderlier)
                            ' X-put reduces the margin
                        End If
                    End If

                Else      ' long put is like selling

                    If underlierCurrentPositionInAP <= 0 Then
                        Return OptionEffect - (qty * mtmUnderlier)
                    Else   ' underlier positive
                        If underlierCurrentPositionInAP >= qty Then
                            Return OptionEffect
                        Else
                            Return OptionEffect - ((qty - underlierCurrentPositionInAP) * mtmUnderlier)
                        End If
                    End If
                End If
        End Select
        MessageBox.Show("Holy BatApples! I could not figure out the impact of " + symbol + " on margin.  I returned $0.")
        Return 0
    End Function


THIS CODE GOES IN THE CONTROLS.VB MODULE ----------------------------------------------------------

  Public Function IsAPEntryValid(sym As String, unit As String) As Boolean
        If sym = "" Or unit = "" Then
            Return False
        End If
        If Not IsNumeric(unit) Then
            Return False
        End If
        sym = sym.Trim()
        If Double.Parse(unit) = 0 And sym <> "CAccount" Then
            Return False
        End If
        If Not (IsAStock(sym) Or IsAnOption(sym) Or sym = "CAccount") Then
            MessageBox.Show("Holy Batpencil! I am afraid I cannot process " + sym + ", Dave.", "Error",
                            MessageBoxButtons.OK, MessageBoxIcon.Error)
            Return False
        End If
        Return True
    End Function