i have 4 textbox in my application..if i did't fill any data in that 4 textbox i want to show error like ..please enter necessary fields..i dono how to check whether the field is filled or empty..and also i used 4 radio buttons in my program. out of 4 i want choose 2 radio buttons. if i did't choose any radio button i want to show error.. what is the code for above questions...