http://kor.i2p/books/The%20C%20Programming%20Language%20by%20K&R/chapter2.html
So we might write #define VTAB '\013' /* ASCII vertical tab */
#define BELL '\007' /* ASCII bell character */ or, in hexadecimal, #define VTAB '\xb' /* ASCII vertical tab */
#define BELL '\x7' /* ASCII bell character */ The complete set of escape sequences is \a alert (bell) character \\ backslash \b backspace \? question mark \f formfeed \' single quote \n newline \" double quote \r carriage return \ ooo octal number \t horizontal tab \x hh hexadecimal number \v vertical tab...