Example Application: Simple Interest II

	Example Application: Simple Interest II

The date picker control is a derivative of the date/time picker control. Like the month calendar control, it allows you to select a date from a calendar. It makes it possible to reduce, even eliminate, the likelihood of mistakes emanating from selecting a date. In this application, we use two date picker controls to let the user select a range of dates. We use that range to calculate the number of days that have elapsed and can be used to evaluate the age (number of days) of a loan.

Practical Learning: Creating the Application

Start a new Window Application named SimpleInterest2
In the Solution Explorer, right-click Form1.vb and click Rename
Type SimpleInterest.vb and press Enter

Design the form as follows:

Control	Text	Name	TextAlign
GroupBox	Loan Preparation
Label	Principal
TextBox	0.00	txtPrincipal	Right
Label	Interest Rate:
TextBox	0.00	txtInterestRate	Right
Label	%
Label	Loan Start Date:
DateTimePicker		dtpStartDate
Label	Loan End Date:
DateTimePicker		dtpLoandEndDate
Label	Periods:
TextBox	1	txtPeriods	Right
Label	days
Button	Calculate	btnCalculate
GroupBox	Results
Label	Interest Earned:
TextBox	0.00	txtInterestEarned	Right
Label	Future Value:
TextBox	0.00	txtFutureValue	Right
Button	Close	btnClose

Right-click the form and click View Code
In the form Class Name combo box, select dtpEndDate

In the Method Name combo box, select CloseUp and implement the event as follows:

Private Sub dtpEndDateCloseUp(ByVal sender As Object, 
                                   ByVal e As System.EventArgs) 
                                   Handles dtpEndDate.CloseUp
        Dim Principal As Double
        Dim InterestRate As Double
        Dim Periods As Double
        Dim InterestEarned As Double
        Dim FutureValue
        Dim StartDate As DateTime
        Dim EndDate As DateTime
        Dim spnPeriods As TimeSpan

        ' Get the value of the principal
        Try
            Principal = CDbl(txtPrincipal.Text)
        Catch
            MsgBox("Invalid Principal Value")
        End Try

        ' Get the interest rate
        Try
            InterestRate = CDbl(txtInterestRate.Text) / 100
        Catch
            MsgBox("Invalid Interest Rate")
        End Try

        ' Get the start and end dates
        StartDate = dtpStartDate.Value
        EndDate = dtpEndDate.Value

        ' Make sure the end date doesn't occur before the start date
        If EndDate < StartDate Then
            MsgBox("Invalid Date Sequence: " & 
                            "the end date must occur after the start date")
            dtpEndDate.Value = DateTime.Today
            Return
        End If

        ' Get the difference in days
        ' The will be the periods
        spnPeriods = EndDate.Subtract(StartDate)
        Dim days As Integer = spnPeriods.Days
        txtPeriods.Text = CStr(days)

        Dim p As Double

        ' Because we will allow the user to directly specify 
        ' the number of days, let's get the period from its text box
        Try
            p = CDbl(txtPeriods.Text)
        Catch ex As Exception
            MsgBox("Invalid number of days")
        End Try

        ' The actual period is gotten as follows
        Periods = p / 365
        ' Now we can perform the calculations
        InterestEarned = Principal * InterestRate * Periods
        FutureValue = Principal + InterestEarned

        ' Display the values
        txtInterestEarned.Text = FormatCurrency(InterestEarned)
        txtFutureValue.Text = FormatCurrency(FutureValue)
End Sub

In the form Class Name combo box, select txtPeriods

In the Method Name combo box, select Leave and implement the event as follows:

Private Sub txtPeriodsLeave(ByVal sender As Object, 
                                 ByVal e As System.EventArgs) 
                                 Handles txtPeriods.Leave
        ' If the user directly enters the number of days
        ' in the Periods text box and press Tab,
        ' we can perform the caltulation
        dtpEndDateCloseUp(sender, e)
End Sub

In the form Class Name combo box, select btnCalculate

In the Method Name combo box, select Click and implement the event as follows:

Private Sub btnCalculateClick(ByVal sender As Object, 
                                   ByVal e As System.EventArgs) 
                                   Handles btnCalculate.Click
        ' If the user directly enters the number of days
        ' in the Periods text box and clicks the Calculate
        ' button, we can perform the caltulation
        dtpEndDateCloseUp(sender, e)
End Sub

In the Class Name combo box, select btnClose

In the Method Name combo box, select Click and implement the event as follows:

Private Sub btnCloseClick(ByVal sender As Object, 
                               ByVal e As System.EventArgs) 
                               Handles btnClose.Click
        End
End Sub

Return to the form
In the Properties window, click the Properties button
On the form, click the top date picker control
In the Properties window, change the following values:
CalendarForeColor: Blue
CalendarMonthBackground: SkyBlue
CalendarTitleBackColor: Navy
CalendarTitleForeColor: Gold
CalendarTrailingForeColor: DodgeBlue
On the form, click the top date picker control
In the Properties window, change the following values:
CalendarForeColor: Maroon
CalendarMonthBackground: Orange
CalendarTitleBackColor: Sienna
CalendarTitleForeColor: Khaki
CalendarTrailingForeColor: White
Execute the application and test the application
Close the form and return to your programming environment

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