http://kor.i2p/books/The%20C%20Programming%20Language%20by%20K&R/chapter2.html
Such expressions may be evaluated at during compilation rather than run-time,
and accordingly may be used in any place that a constant can occur, as in #define MAXLINE 1000
char line[MAXLINE+1]; or #define LEAP 1 /* in leap years */
int days[31+28+LEAP+31+30+31+30+31+31+30+31+30+31]; A string constant , or string literal , is a sequence of zero
or more characters surrounded by double quotes, as in "I am a string" or "" /* the empty string */ The quotes are not part of the string,...