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 is
usually ^Z under Windows) and that ^C is the interrupt
character. In most contexts, the term
terminated by a full stop (.) can be typed instead of the EOF