Department of Engineering

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Keywords

You can't use the following reserved words for variable names, etc.

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

A few of these haven't yet been described.

auto

:- This is the default Storage Class for variables so it's not explicitly used. static, which you've already met, is an alternative class.

const

:- If a variable isn't meant to change you can define it as const. E.g., If you create an integer using `const int i = 6;' then a later `i = 7;' will be illegal. However, if you create a pointer to i and use this to change the value, you'll probably get away with it. The main purpose of const is to help optimisers. volatile is the opposite of const.

enum

:- C has enumerated types, like pascal. E.g.

enum color {Red, Green, Blue};

They're not as useful as in pascal because C doesn't check if you set an enumerated type to a valid value.

register

:- You can suggest to the compiler that a variable should be kept in a register for faster access. E.g. `register int i' might help if i is a much-used indexing variable. An optimising compiler should use registers efficienty anyway. Note that you can't use the `&' operator on a register variable.