I'm having problems with if statements
present value (PV) should be no larger than $10000
interest rate is not higher than 10 and no less than 2
and number of years at least 3

I've tried the if statements with error messageboxs but I was getting confused with all the if's and the messagebox didn't show up right. The following code is my code before entering the if's. Any insight would be very helpful, thank you.

Public Class Form1

    Public Function FV(ByVal PV As Object, ByVal i As Object, ByVal n As Object) As Object
        'Formula to calculate Future Value(FV)
        'PV denotes Present Value
        FV = PV * (1 + i / 100) ^ n

    End Function

    Private Sub compute_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles compute.Click
        'This procedure will calculate Future Value
        Dim FutureVal As Decimal
        Dim PresentVal As Decimal
        Dim interest As Object
        Dim period As Object

        PresentVal = PV.Text
        interest = rate.Text
        period = years.Text
        FutureVal = FV(PresentVal, interest, period)
        lblFV.Text = FormatCurrency(FutureVal)

    End Sub


    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
        Me.Close()
    End Sub


End Class

I'm assuming you want to check the values before making the call to the FV function. If that's the case, you could accomplish what you're trying to do with three simple if statements. Something like the following would probably work just fine:

Private Sub compute_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles compute.Click
'This procedure will calculate Future Value
Dim FutureVal As Decimal
Dim PresentVal As Decimal
Dim interest As Object
Dim period As Object
PresentVal = PV.Text
interest = rate.Text
period = years.Text

If CDbl(PresentVal) > 10000.00 Then
MessageBox.Show("Present Value must not be larger than 10000")
End Sub
End If
If CDbl(interest) < 2 Or CDbl(interest) > 10 Then
MessageBox.Show("Interest Rate must be between 2 and 10")
End Sub
End If
If CInt(period) < 3 Then
MessageBox.Show("The Period must be at least 3 years")
End Sub
End If

FutureVal = FV(PresentVal, interest, period)
lblFV.Text = FormatCurrency(FutureVal)
End Sub

If you just need something simple, this should work. You may want to change the conversions depending on what you're assuming will be input from the text fields, and you would obviously want to use some kind of exception handling anytime you're converting the text from user input into various data types.

Comments
A GREAT HELP THANK YOU !!

The way I should implement is : using the LostFocus event for the textboxes. After the lostfocus you can warn a user corresponding the maximum or minimum values needed. Second is creating yourself a class in which you calculate the FV.

code below:

Public Class Class1
    Private _FutureValue As Decimal
    Private _PresentVal As Decimal
    Private _Interest As Double
    Private _Period As Integer
   'just for remembering the formula (for me :=) )
    Private Const CN_Formula As String = "FV = PV * (1 + i / 100) ^ n"

    Public Property FutureValue() As Decimal
        Get
            Return _FutureValue
        End Get
        Set(ByVal value As Decimal)
            _FutureValue = value
        End Set
    End Property
    Public Property PresentVal() As Decimal
        Get
            Return _PresentVal
        End Get
        Set(ByVal value As Decimal)
            _PresentVal = value
        End Set
    End Property
    Public Property Interest() As Double
        Get
            Return _Interest
        End Get
        Set(ByVal value As Double)
            _Interest = value
        End Set
    End Property
    Public Property Period() As Integer
        Get
            Return _Period
        End Get
        Set(ByVal value As Integer)
            _Period = value
        End Set
    End Property
    Public Function Calculate() As Decimal
        Try
            Return Me.PresentVal * (1 + Me.Interest / 100) ^ Me.Period
        Catch ex As Exception
            Throw New ArgumentException("For some reason no calculation could be done!")
        End Try

    End Function

    Public Sub New()
        MyBase.New()
    End Sub
End Class

formcode:

Public Class Form1
    Private myCalc As Class1 = New Class1
    Private Sub TextBox1_TextChanged(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles TextBox1.TextChanged
        Try
            myCalc.PresentVal = CType(DirectCast(sender, TextBox).Text, Decimal)
        Catch ex As Exception
            MsgBox(ex.Message)
        End Try
    End Sub


    Private Sub TextBox2_TextChanged(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles TextBox2.TextChanged
        Try
            myCalc.Period = CType(DirectCast(sender, TextBox).Text, Double)
        Catch ex As Exception
            MsgBox(ex.Message)
        End Try
    End Sub

    Private Sub TextBox3_TextChanged(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles TextBox3.TextChanged
        Try
            myCalc.Interest = CType(DirectCast(sender, TextBox).Text, Integer)
        Catch ex As Exception
            MsgBox(ex.Message)
        End Try
    End Sub

    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
        Try
            Me.TextBox4.Text = myCalc.Calculate
        Catch ex As Exception
            MsgBox(ex.Message)
        End Try

    End Sub
End Class
This question has already been answered. Start a new discussion instead.