C - Reserved Keywords

The following names are reserved by the C language. Their meaning is already defined, and they cannot be re-defined to mean anything else.

auto	else	long	switch
break	enum	register	typedef
case	extern	return	union
char	float	short	unsigned
const	for	signed	void
continue	goto	sizeof	volatile
default	if	static	while
do	int	struct	_Packed
double

While naming your functions and variables, other than these names, you can choose any names of reasonable length for variables, functions etc.