Check if String is Number or not using C# and VB.Net

Hi Hafifiw,

 Please refer below sample.

HTML

<asp:TextBox runat="server" ID="txtNumber" />
<asp:Button ID="btnSubmit" runat="server" Text="Submit" OnClick="OnSubmit" />

Code

C#

protected void OnSubmit(object sender, EventArgs e)
{
    string number = txtNumber.Text;
    for (int i = 0; i < number.Split(',').Length; i++)
    {
        bool isNumber = IsNumeric(number.Split(',')[i]);
        if (!isNumber)
        {
            ClientScript.RegisterStartupScript(this.GetType(), "alert", "alert('" + number.Split(',')[i] + " is not a number.');", true);
            break;
        }
    }
}

public bool IsNumeric(string value)
{
    return value.All(char.IsNumber);
}

VB.Net

Protected Sub OnSubmit(ByVal sender As Object, ByVal e As EventArgs)
    Dim number As String = txtNumber.Text
    For i As Integer = 0 To number.Split(","c).Length - 1
        Dim isNumber As Boolean = IsNumeric(number.Split(","c)(i))
        If Not isNumber Then
            ClientScript.RegisterStartupScript(Me.GetType(), "alert", "alert('" & number.Split(","c)(i) & " is not a number.');", True)
            Exit For
        End If
    Next
End Sub

Public Function IsNumeric(ByVal value As String) As Boolean
    Return value.All(AddressOf Char.IsNumber)
End Function

Screenshot