C Programming Keywords and Identifiers

In this tutorial, you will learn about keywords; reserved words in C programming that are part of the syntax. Also, you will learn about identifiers and proper way to name a variable.

Character set

Character set is a set of alphabets, letters and some special characters that are valid in C language.

Alphabets

Uppercase: A B C ................................... X Y Z
Lowercase: a b c ...................................... x y z

C accepts both lowercase and uppercase alphabets as variables and functions.

Digits

0 1 2 3 4 5 6 7 8 9

Special Characters

Special Characters in C Programming

,	<	>	.	_
(	)	;	$	:
%	[	]	#	?
'	&	{	}	"
^	!	*	/	|
-	\	~	+

White space Characters

blank space, new line, horizontal tab, carriage return and form feed

C Keywords

Keywords are predefined, reserved words used in programming that have special meanings to the compiler. Keywords are part of the syntax and they cannot be used as an identifier. For example:

int money;

Here, int is a keyword that indicates 'money' is a variable of type integer. 

As C is a case sensitive language, all keywords must be written in lowercase. Here is a list of all keywords allowed in ANSI C.

Keywords in C Language

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

Along with these keywords, C supports other numerous keywords depending upon the compiler.

All these keywords, their syntax and application will be discussed in their respective topics. However, if you want a brief overview on these keywords without going further, visit list of all keywords in C programming.

C Identifiers

Identifier refers to name given to entities such as variables, functions, structures etc.

Identifier must be unique. They are created to give unique name to a entity to identify it during the execution of the program. For example:

int money;
double accountBalance;

Here, money and accountBalance are identifiers.

Also remember, identifier names must be different from keywords. You cannot use int as an identifier because int is a keyword.

Rules for writing an identifier

1. A valid identifier can have letters (both uppercase and lowercase letters), digits and underscores.
2. The first letter of an identifier should be either a letter or an underscore. However, it is discouraged to start an identifier name with an underscore.
3. There is no rule on length of an identifier. However, the first 31 characters of identifiers are discriminated by the compiler.

Good Programming Practice

You can choose any name for an identifier (excluding keywords). However, if you give meaningful name to an identifier, it will be easy to understand and work on for you and your fellow programmers.