Check TextBox value for NAN (Not A Number) in ASP.Net using C# and VB.Net

Hi lingers,

Check this example. Now please take its reference and correct your code.

HTML

Enter Number:
<asp:TextBox ID="TextBox1" runat="server"></asp:TextBox>
<asp:Button ID="Button1" runat="server" Text="Submit" OnClick="Button1_Click" />
<br />
<asp:Label ID="Label50" runat="server"></asp:Label>

Code

C#

protected void Button1_Click(object sender, EventArgs e)
{
    Label50.Text = IsDoubleNaN(TextBox1.Text);
}

public string IsDoubleNaN(string text)
{
    if (string.IsNullOrEmpty(text))
    {
        return "it's not a number";
    }
    Double num = 0;
    bool isDouble = Double.TryParse(text, out num);

    return isDouble ? "it's a number" : "it's not a number";
}

VB.Net

Protected Sub Button1_Click(ByVal sender As Object, ByVal e As EventArgs)
    Label50.Text = IsDoubleNaN(TextBox1.Text)
End Sub

Public Function IsDoubleNaN(ByVal text As String) As String
    If String.IsNullOrEmpty(text) Then
        Return "it's not a number"
    End If
    Dim num As Double = 0
    Dim isDouble As Boolean = Double.TryParse(text, num)

    Return If(isDouble, "it's a number", "it's not a number")
End Function

Screenshot