How to automatically generate primary key in textbox.

Question

Dear All,
           I have designed one form as client in this form i take ADD, UPDATE etc button to insert , update databse. In client database table client id is primary key and in my user interface i have take one textbox for client id to enter the primary key value.  
          But my question is i want to generate the value of the primary key or client id is automatically generated i dont want that user enter the primary key value when i click ADD button.
          Hope that you get my question.  Thanks for your time and consideration. I look forward to receive reply. 

Thanks & Regards

 Farukh