Keyword and Identifier

                                                              Keywords:    

Keywords are the reserved words used in programming. Each keywords has fixed meaning and that cannot be changed  by user.

For example:

Int x;

Here , int is a keyword that indicates, ‘x’ is of type integer.

As, C programming is case sensitive , all keywords must be written in lowercase.

Here is the list of 32 keywords  predefined by ASCII C.

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

                                                               Identifier:

In C programming , identifiers are names given to C entities, Such as variables, functions, structures etc.

Identifier are created to give unique name to C entities to identify it during the execution of  program.

For example:

Int deep;

 Here, deep is identifier which  denotes a variable of type integer.

Rules for writing identifier:

1)       An identifier can be composed of letters(both uppercase and lowercase letters), digits and underscores ‘_’ only.

2)       The first letter of identifier should be either a letter or an underscore.

3)       There is no rule for the length of an identifier. However, the first 31 character of an identifier are discriminated by the compiler.

So, the first 31 letters of two identifier in a program should be different.