Standard C Keywords
break     
case      
char      
const     
continue
default
do
else
for
goto
if
return
switch
void
while

C Preprocessor directives
#define
#error
#include
#pragma

Questionable C Keywords
enum
extern
register
signed
sizeof
struct
typedef
union
unsigned
volatile

Unused Standard C Keywords
auto      n/a
double    n/a
float     n/a
int       n/a  
long      n/a
short     n/a
static    n/a

Unused Preprocessor Directives
#if
#ifdef
#ifndef
#undef
# line