How to type control characters into a file using Vi

Its simple.. For example if you need to write ^@ in a file in unix
1. Open the file in insert mode using vi
2. Use the keys in the order they have been listed
(ctrl+v) + (ctrl+@)
All it means is keep the ctrl key pressed and use v & @ in close succession

Vi quick hack to get the arrow keys working normally

:set nocompatible