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5.3 Whitespace

Whitespace means characters that exist in a file but appear blank in a printed listing of a file (or traditionally did appear blank, several decades ago). The C language requires whitespace in order to separate two consecutive identifiers, or to separate an identifier from a numeric constant. Other than that, and a few special situations described later, whitespace is optional; you can put it in when you wish, to make the code easier to read.

Space and tab in C code are treated as whitespace characters. So are line breaks. You can represent a line break with the newline character (also called linefeed or LF), CR (carriage return), or the CRLF sequence (two characters: carriage return followed by a newline character).

The formfeed character, Control-L, was traditionally used to divide a file into pages. It is still used this way in source code, and the tools that generate nice printouts of source code still start a new page after each “formfeed” character. Dividing code into pages separated by formfeed characters is a good way to break it up into comprehensible pieces and show other programmers where they start and end.

The vertical tab character, Control-K, was traditionally used to make printing advance down to the next section of a page. We know of no particular reason to use it in source code, but it is still accepted as whitespace in C.

Comments are also syntactically equivalent to whitespace.