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Help Figuring Out Calculating Payment with VB

Posted on 2013-05-10
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Last Modified: 2013-05-13
I am trying to program a mortgage type calculator with Visual Basic and can't quite figure out the code.
    Private Sub calcbutton_Click(sender As System.Object, e As System.EventArgs) Handles calcbutton.Click
        'The car price should appear in terms of dollars and cents.
        Dim carprice As Double
        'The APR needs two percentage points
        Dim interestrate As Double
        'Money down should be dollars and cents
        Dim moneydown As Double
        'Dim loan term As Double
        Dim loanterm As Double
        'Dim Payment as Double
        Dim payment As Double
        Dim monthlyinterest As Double
        Dim months As Double
        Dim loanamount As Double

        'Declare where the values are coming from
        carprice = Val(Carpricetext.Text)
        interestrate = Val(IRTextbox.Text)
        moneydown = Val(Dwnpymnttext.Text)
        loanterm = Val(LnTrmList.SelectedValue)
        loanamount = (carprice - moneydown)






        Do While loanterm <= 5
            monthlyinterest = (interestrate / 100) / 12
            months = 12 * loanterm

            'calculate payments - rate * month = monthly payments
            payment = _
                Pmt(monthlyinterest, months, -loanamount)


            'displays results
            paymenttxt.Text = payment


        Loop
    End Sub

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When I debug this:
            payment = _
                Pmt(monthlyinterest, months, -loanamount)
This tells me Argument 'NPer' is not a valid value.

Any ideas on what I need to do?
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Question by:aclaus225
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4 Comments
 
LVL 12

Expert Comment

by:funwithdotnet
ID: 39156508
It looks like somewhere along the line, months ends up = 0.
Just in case, you might try:
loanterm = CDbl(LnTrmList.SelectedValue)

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You can also break on line 34, look at the values of the arguments and backtrack from there.
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LVL 22

Expert Comment

by:mcsween
ID: 39156525
NPer is the second argument in the Pmt function.  It's complaining it doesn't like the value for month.  

Add the following line after months = 12 * loanterm to see what is actually being set for months.  You may have to use the CInt function to cast it to an integer.
MsgBox(months)

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Author Comment

by:aclaus225
ID: 39156602
mcsween,

The message box popped up "0" so would that indicate the the program is not reading what is in the list box LnTrmList.SelectedValue?
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Accepted Solution

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Mike Tomlinson earned 2000 total points
ID: 39162189
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