How to Replace NaN with zero or a message?

I tried anything like in if statement but I dont know what should i type in order to replace NaN with a zero or a message like "empty"


please help me guys im just new to Ms Visual Studio 2010

thanks in advance





Private Sub btnCompute_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnCompute.Click
If txtA.Text = Nothing Then
MessageBox.Show("textbox A value is Missing! please input a value", Me.Text, MessageBoxButtons.OK, MessageBoxIcon.Error)
txtA.Focus()
Exit Sub
End If
If txtB.Text = Nothing Then
MessageBox.Show("textbox B value is Missing! please input a value", Me.Text, MessageBoxButtons.OK, MessageBoxIcon.Error)
txtB.Focus()
Exit Sub
End If
If txtC.Text = Nothing Then
MessageBox.Show("textbox C value is Missing! please input a value", Me.Text, MessageBoxButtons.OK, MessageBoxIcon.Error)
txtC.Focus()
Exit Sub
End If


Dim a, b, c, x1, x2 As Double


a = Val(txtA.Text)
b = Val(txtB.Text)
c = Val(txtC.Text)

x1 = Format(Val(-b + Math.Sqrt(b ^ 2 - 4 * a * c)) / (2 * a), "#,###.00")

x2 = Format(Val(-b - Math.Sqrt(b ^ 2 - 4 * a * c)) / (2 * a), "#,###.00")

lblOutput2.Text = "{" & x1 & " , " & x2 & "}"

If txtA.Text = Nothing Then
lblOutput2.Text = "no value computed!"
ElseIf txtB.Text = Nothing Then
lblOutput2.Text = "no Value Computed!"
ElseIf txtC.Text = Nothing Then
lblOutput2.Text = "no value Computed!"
ElseIf txtA.Text = 0 Then
MessageBox.Show("Invalid Divisor!, put a valid numeric VALUE!", Me.Text, MessageBoxButtons.OK, MessageBoxIcon.Error)
lblOutput2.Text = "Invalid"
ElseIf lblOutput2.Text = is Then
lblOutput2.Text = "ERROR!"
End If

End Sub

Actually, rather than replacing NAN, you should perform a check before the function to ensure that the result is never NAN. This will require a couple steps.

For one thing, Val is risky. It would be better to use Double.TryParse, but that won't truly solve the problem. After all, no matter what you do, if a=0, the equations will result in NAN. The risk of Val is that if the user enters a comma, you will get a number, but not the number you expected, and so forth. However, if you check that a <> 0, then you can avoid performing the equation for cases when a = 0, and NAN will never occur. You can scold the user if you wish, at that point.

By the way, txtA.Text will never be Nothing, and that isn't the way to test for Nothing anyways. It would look like:

If txtA.Text Is Nothing Then

However, since it will never be nothing, that isn't really worth doing. Check for this:

If txtA.Text = String.Empty Then

or else

If txtA.Text = "" Then

Additionally, in VS 2010, there is a new string function String.IsNullOrWhiteSpace(txtA.text) which checks if the textbox is empty, equals Nothing (which in the case of the textbox is never the case), or is just filled with white space.