Nguyễn Đình Đại

You could join an online tutorials for learn how to programming. Ex tutorialspoint

can you try this: int price = 0; try { price = Integer.parseInt(request.getParameter("price")); } catch(NumberFormatException e) { // log the error or ignore it // Ex: price = -1; }

I think this link will help you: http://stackoverflow.com/questions/3069416/difference-between-string-and-stringbuilder-in-c-sharp

you should be using mvc design pattern for you project!