editable column in gridview dynamically

      I have a two textboxes and one gridview. I retrieve related data from the database and add it the gridview.but i need to add the extra one column with editable after bind the data. for example ( when i select the class name and exam name then my gridview bind all the student details  with editable column for enter marks for that particular exam. I have done this task before in the windows application. but in web appication i cannnot able to do it. please help me to solve the problem.   

 Thank you