I want to add a specific class to an input if an error is genereted by the input.

For example, if input is empty and has required validator it shouls look like this:

<dd id="login-element">
    <input type="text" name="login" id="login" value="" class="input-text error" />
    <ul class="errors">
        <li>Value is required and can't be empty</li>
    </ul>
</dd>

class="input-text error"

Please tell me how to do that.