* CPP

CPP symbols:
	syntax
	conditional code inclusion
	a table of symbols -> value (can be undef or "0"!)
	header definitions
	
gcc -v tells you symbols

	#define
	#undef
	#ifdef
	#ifndef
	#else
	#if CPP EXPR

#if EXPR
	evalues an expression!  if EXPR symbol is #define'd, may not have a
	value or some default value that may not evaluate to '1'!