#include <stdio.h>	includes contents of stdio.h
#error text	display text as compile time error
#warning text	display text as compile time warning
#pragma	compiler specific options
#define M	define M
#undef M	undefine M
#if (condition)	conditional compiling
#ifdef M	compiled if M is defined
#ifndef M	compiled if M is not defined
#elif (condition)	conditional compiling
#else	conditional compiling
#endif	end conditional section
defined()	is macro defined.
!defined()	is macro not defined
M ## D	combines M and D into MD
#M	treat M as string "M"