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Subtracting numbers from two text boxes

I dynamically populate rows of data. I need to get the amount due for a line item.

Items from DB:
OriginalAmount = Dollar amount owed
totalPayment = How much has been paid so far.

Input items:
txtAmtPatientPaid = input box
txtAmtPaid = input box

The user fills out the form and I use Javascript to update the AmtDueTemp field which works correctly. When the user hits the 'Save' button the validation is run on the .aspx.vb page. If there is an error I want all populated fields to remain populated on postback.

If I only subtract the amount from the DB it works but now I need to subtract the two input box fields. How can I do the calculation below? I believe I need to change the field type to a number but I don't know how.

Any suggestions?

dblAmtDueTemp = FormatNumber(rd("OriginalAmount") - rd("totalPayment") - Request.Form("txtAmtPatientPaid" & i) - Request.Form("txtAmtPaid" & i), 2)

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kaufmed

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Jacque Scott

ASKER

I still get the same error:

Input string was not in a correct format

Jacque Scott

ASKER

I did not use the 'Try' or 'Catch'. Would that make a difference?

I also used convert.ToDouble and got the same error.

Jacque Scott

ASKER

Once I added the 'Try' and 'Catch' it worked.

What does that do?

kaufmed

It shouldn't make a difference--you just will have an unhandled exception if the values passed to Convert.ToDecimal (or ToDouble) do not represent valid numbers.

See if this works better:

Try
    dblAmtDueTemp = Convert.ToDouble(rd("OriginalAmount")) - Convert.ToDouble(rd("totalPayment")) - Convert.ToDouble(Request.Form("txtAmtPatientPaid" & i)) - Convert.ToDouble(Request.Form("txtAmtPaid" & i))
Catch ex As System.FormatException
    ' Conversion failed
End Try

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Jacque Scott

ASKER

I thought it worked but it doesn't. Because of the 'Try' and 'Catch' it gives a number and not an error but it doesn't calculate correctly and then all the rows get the same number.

kaufmed

With which version?

Jacque Scott

ASKER

Both.

I ended up doing the below:

If Request.Form("txtAmtPatientPaid" & i) = "" Then
                                                dblAmtPatientPaidtemp = 0
                                            Else
                                                dblAmtPatientPaidtemp = Request.Form("txtAmtPatientPaid" & i)
                                            End If
                                            If Request.Form("txtAmountPaid" & i) = "" Then
                                                dblAmtPaidtemp = 0
                                            Else
                                                dblAmtPaidtemp = Request.Form("txtAmountPaid" & i)
                                            End If
                                            dblAmtDueTemp = FormatNumber(rd("OriginalAmount") - rd("totalPayment") - (dblAmtPatientPaidtemp + dblAmtPaidtemp), 2)

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