When I try to run the program to calculate payment and total intrest I get \"Con

Question

When I try to run the program to calculate payment and total intrest I get "Conversion from string "" to type 'Double' is not valid."

What am I doing wrong?

Dim P As Double
Dim R As Double
Dim N As Double
Dim Payment As Double
Dim totalInterest As Double

Private Sub btnAnalyze_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnAnalyze.Click

P = CDbl(txtAmount.Text)
N = CDbl(txtDuration.Text)
R = CDbl(txtInterestRate.Text)

Payment = (P * R) / (1 - (1 + R) ^ (-N))
totalInterest = (N * Payment) - P

Payment = CDbl(txtPayment.Text)
totalInterest = CDbl(txtInterest.Text)

If P < 0 Then
MessageBox.Show("Please enter in loan amount")

End If

If R <= 0 Then
MessageBox.Show("Please enter in loan amount")

End If

If N <= 0 Then
MessageBox.Show("Please enter in loan amount")

End If


End Sub
End Class

Explanation / Answer

Conversion from string "" to type 'Double' is not valid." It's complaining about when string is empty,so add if statements to take care of that. ____________________________________________ Dim P As Double Dim R As Double Dim N As Double Dim Payment As Double Dim totalInterest As Double Private Sub btnAnalyze_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnAnalyze.Click If txtAmount.Text="" Then txtAmount.Text=0 End If If txtDuration.Text="" Then txtDuration.Text=0 End If If txtInterestRate.Text="" Then txtInterestRate.Text=0 End If P = CDbl(txtAmount.Text) N = CDbl(txtDuration.Text) R = CDbl(txtInterestRate.Text) Payment = (P * R) / (1 - (1 + R) ^ (-N)) totalInterest = (N * Payment) - P Payment = CDbl(txtPayment.Text) totalInterest = CDbl(txtInterest.Text) If P < 0 Then MessageBox.Show("Please enter in loan amount") End If If R

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