When referring to keyboard characters, printing characters are written thus: a, while control characters are written like this: ^A. Thus ^C is the character you get by holding down the <CTL> key while you type c. Finally, the special control characters carriage-return, line-feed and space are often abbreviated to <RET>, <LFD> and <SPC> respectively.
Throughout, we will assume that ^D is the EOF character (it's
usually ^Z under Windows) and that ^C is the interrupt character.
In most contexts, the term end_of_file terminated by a full stop
(.) can be typed instead of the EOF character.