Keywords and identifiers

Keywords

Like every computer language, C has a set of reserved words often known as keywords that cannot be used as identifier. All keywords are basically a sequence of characters that have a fixed meaning.By convention all Keywords must be written in lowercase letters.

Keywords in C language

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

Identifiers

Identifiers, as the name suggests helps us to identify data and other objects in the program. Identifiers are basically the name given to program elements such as variables,arrays, and functions Identifiers may consist of an alphabet,digit or an underscore.

Rules for Forming identifier Names

Some rules have to be followed while forming identifiers names.

• It cannot include any special characters or punctuation marks(like #, $, ^, ?, ., etc)except the underscore'_'
• There cannot be two successive underscores.
• Keywords cannot be used as identifiers.
• The case of alphabet characters that form the identifier name is significant. For example "FIRST" is different from 'first' and 'First'.
• The identifier name must begin with an alphabet or an underscore. However,use of underscore as the first character must be avoided because several compiler-defined identifiers in the standard C library have underscore as their first character.
• Identifiers can be of any reasonable length. They should not contain more than 31 characters.It can actually be longer than 31, but the compiler looks at only the first 31 characters of the name.