validation for lenght of the textbox

required and then you'll need a custom

[aspx]

<asp:TextBox ID="txtCred" runat="server" MaxLength="16" />
      <asp:RequiredFieldValidator
         ID="RequiredFieldValidator1" ControlToValidate="txtCred" runat="server" ErrorMessage="Must enter Credit Card number!"></asp:RequiredFieldValidator>
       <asp:CustomValidator ControlToValidate="txtCred" ID="CustomValidator1"
           runat="server" ErrorMessage="Must be 16 characters long!"
           onservervalidate="CustomValidator1_ServerValidate"></asp:CustomValidator>
[C#]

protected void CustomValidator1_ServerValidate(object source, ServerValidateEventArgs args) {
      args.IsValid = args.Value.Length == 16;
   }

You can use a custom validator or you can do it manually with textbox.text.length

is there anyway to not user code behind? or have to for that?

why don't you want to use the code behind??

you can do it inline...

<script language="C#" runat="server">
      protected void CustomValidator1_ServerValidate(object source, ServerValidateEventArgs args) {
      args.IsValid = args.Value.Length == 16;
   }
    </script>

Many people write code this way. You will need the extra .cs file.

what is actually differrent between writing protected void in Javascript and codebehind. which one is better? also do I need to add anthing in CompareValidator1 ?

Thank you!