POS / 408 MortgagePaymentCalculator

MortgagePaymentCalculator.vb

'
' File: MortgagePaymentCalculator.vb
' Author: Billy Coover
' Date: March 11, 2011
' 
' Change request 16 from SR-mf-003.  Create a VB.NET program that calculates and displays the monthly
' payment for a $200,000 loan at 5.75% interest for 30 years
' 
' Quality Control
' Version 0   | 03/11/2011 | Write the program in VB.Net (not Web based) using a loan amount of $200,000 with an interest rate of 5.75% and a 30 year term. Display the mortgage payment amount. Insert comments to document the program. There is No Requirement for the user to enter values.
' Version 0.1 | 03/11/2011 | Added a Mortgage object rather than just hard coding mortgage amounts.
' Version 0.2 | 03/11/2011 | Created and tested the calculation for the monthly mortgage amount.
' Version 1.0 | 03/18/2011 | Change to prompt for user input
' Version 1.1 | 03/18/2011 | Added amortization schedule to payment calc class
' Version 2.0 | 03/22/2011 | Added mortgage list and looped through the list to calculate the pauments for each mortgage
' Version 2.1 | 03/29/2011 | Added mortgage list and looped through the list to calculate the pauments for each mortgage
' Version 3.0 | 03/29/2011 | Added mortgage list and looped through the list to calculate the pauments for each mortgage and display amortization schedule
' Version 3.1 | 03/31/2011 | Fixed a bug in the payment calc
' Version 3.2 | 04/01/2011 | Fixed another bug in the payment calc

Imports System
Imports System.Diagnostics
Imports System.Threading
Imports System.Collections.Generic

Namespace pos408
    ''' <summary>
    ''' Mortgage payment calculator
    ''' </summary>
    Class MortgagePaymentCalculator

        'local variables
        Public Shared mortgages As List(Of Mortgage)
        Public Const principal As [Double] = 200000.0
        Public Shared paymentCalculator As PaymentCalculator

        ''' <summary>
        ''' Maint entry point of the program
        ''' </summary>
        ''' <param name="args">
        ''' null for this application
        ''' </param>
        Public Shared Sub Main(ByVal args As String())
            'Create a list of mortgages
            mortgages = New List(Of Mortgage)()
            mortgages.Add(New Mortgage() With { _
             .Principal = principal, _
             .InterestRate = 0.0535, _
             .Term = 7 _
            })
            mortgages.Add(New Mortgage() With { _
                .Principal = principal, _
                .InterestRate = 0.055, _
                .Term = 15 _
            })
            mortgages.Add(New Mortgage() With { _
                .Principal = principal, _
                .InterestRate = 0.0575, _
                .Term = 30 _
            '})

            'Iterate through the list of mortages and calculate the payment amount
            For i As Integer = 0 To mortgages.Count - 1
                Dim counter = i + 1
                paymentCalculator = New PaymentCalculator(mortgages(i))
                'Print the mortgage properties to screen
                Console.Write(
                    [String].Format(
                              "Mortgage {0} principal amount is: {1}",
                              counter,
                              mortgages(i).Principal) + Environment.NewLine)
                Console.Write(
                    [String].Format(
                        "Mortgage {0} term is: {1}",
                        counter,
                        mortgages(i).Term) + Environment.NewLine)
                Console.Write(
                    [String].Format(
                        "Mortgage {0} interest rate is: {1}",
                        counter,
                        mortgages(i).InterestRate) + Environment.NewLine)

                'Print the calculated mortgage amount in currency format
                Console.Write(
                    [String].Format(
                        "The monthly payment amount is for mortgage {0} is: {1} " & vbLf,
                        counter,
                        paymentCalculator.CalculatePayment().ToString("c")) + Environment.NewLine)
                'Print the amortization schedule
                paymentCalculator.PrintAmortizationSchedule()

            Next
        End Sub
    End Class

    ''' <summary>
    ''' A mortgage object to store properties of a mortgage
    ''' </summary>
    Class Mortgage

        Public Property Principal() As Double
            Get
                Return m_Principal
            End Get
            Set(ByVal value As Double)
                m_Principal = Value
            End Set
        End Property
        Private m_Principal As Double
        Public Property InterestRate() As Double
            Get
                Return m_InterestRate
            End Get
            Set(ByVal value As Double)
                m_InterestRate = Value
            End Set
        End Property
        Private m_InterestRate As Double
        Public Property Term() As Integer
            Get
                Return m_Term
            End Get
            Set(ByVal value As Integer)
                m_Term = Value
            End Set
        End Property
        Private m_Term As Integer

        Public ReadOnly Property MonthlyInterestRate() As Double
            Get
                Return InterestRate / 12
            End Get
        End Property

        Public ReadOnly Property TermInMonths() As Double
            Get
                Return Term * 12
            End Get
        End Property
    End Class

    ''' <summary>
    ''' A payment calculator object that accepts a mortgage object and calculates a monthly payment amount
    ''' </summary>
    Class PaymentCalculator

        Public mortgage As Mortgage

        Public Sub New(ByVal mortgage As Mortgage)
            Me.mortgage = mortgage
        End Sub

        ' Calculates the monthly mortgage payment
        Public Function CalculatePayment() As Double
            Return (
                (Me.mortgage.Principal *
                (Me.mortgage.InterestRate / 12)) /
                 (1 - Math.Pow(1 + (Me.mortgage.InterestRate / 12), -Me.mortgage.TermInMonths)))
        End Function

        ' Prints the amortization schedule to screen
        Public Sub PrintAmortizationSchedule()
            'Initial variables
            Dim paymentNumber As Integer = 0
            Dim loopIteration As Integer = 0
            Dim principalBalance As Double = Me.mortgage.Principal
            Dim monthlyInterestRate As Double = Me.mortgage.MonthlyInterestRate
            Dim monthlyPayment As Double = Me.CalculatePayment()
            Dim currentMonthlyInterest As Double
            Dim currentMonthlyPrincipal As Double
            Dim rollingInterest As Double = 0
            Dim rollingPrincipal As Double = 0

            'basic while loop that goes until the balance is zero or less
            While principalBalance > 1

                'Cycle the payment number for display
                paymentNumber += 1

                'Calculate current monthly interest
                currentMonthlyInterest = principalBalance * monthlyInterestRate

                'Calculate this month's Principal payment
                currentMonthlyPrincipal = monthlyPayment - currentMonthlyInterest

                'Calculate the new principal balance of the loan after last payment        
                principalBalance = principalBalance - currentMonthlyPrincipal

                'add rolling balances
                rollingInterest = rollingInterest + currentMonthlyInterest
                rollingPrincipal = rollingPrincipal + currentMonthlyPrincipal

                'print payment #, interest paid, and loan balance
                Console.WriteLine(
                    "Payment # " + paymentNumber.ToString() + ": Interest paid: " _
                    + currentMonthlyInterest.ToString("c") + " Loan balance: " _
                    + principalBalance.ToString("c"))

                'Cycle the loop counter
                loopIteration += 1

                'Print n times, then hesitate if there is still a remaining balance
                If principalBalance > 0 AndAlso loopIteration >= 10 Then
                    loopIteration = 0
                    Console.WriteLine(vbLf & " Calculating next group of payments... " & vbLf)
                    Try
                        'sleep for 1000 ms
                        System.Threading.Thread.Sleep(200)
                        'Supress the error for now
                    Catch
                    End Try
                End If
            End While
            Console.WriteLine(vbLf & " Amortization schedule complete." & vbLf)
            Console.WriteLine("Total cost of taking the loan to term: " + (rollingInterest + rollingPrincipal).ToString("c") & vbLf)
            Try
                'sleep for 1000 ms
                System.Threading.Thread.Sleep(3000)
                'Supress the error for now
            Catch
            End Try
        End Sub

    End Class

End Namespace