How to check first character is numeric in TextBox in ASP.Net

Dear Band.Atul,

<div>
        <asp:TextBox ID="txtValue" runat="server" />
        <asp:Button Text="Submit" runat="server" OnClick="Submit" />
        <asp:Label ID="lblErrorMessage" Style="color:Red" runat="server" />
</div>

On Coding side i validate on button click see below code.

protected void Submit(object sender, EventArgs e)
        {
            string value = txtValue.Text;
            char val  = value.First();
            if (val < 48 || val > 57)
            {
                lblErrorMessage.Text = "Valid";
            }
            else
            {
                lblErrorMessage.Text = "Invalid";
            }
            
        }

For any issue revert, so we can help you more. Regards Sajid Dhukka