Keywords and Identifiers in C Programming

Keywords

Keywords are predefined words that have a specific meaning and purpose. These words cannot be used as variable names, function names, or any other identifier names.

Below is the list of keywords in C:

Keyword	Description	Keyword	Description
auto	automatic storage duration	break	exit a loop or switch
case	specify a case in a switch	char	character type
const	constant value	continue	skip to the next iteration of a loop
default	default case in a switch	do	execute a loop
double	double precision floating point	else	conditional execution
enum	enumeration type	extern	external variable or function
float	single precision floating point	for	execute a loop
goto	jump to a labeled statement	if	conditional execution
int	integer type	long	long integer type
register	register storage class	return	return from a function
short	short integer type	signed	signed integer type
sizeof	evaluate the size of a type or variable	static	static storage duration
struct	structure type	switch	multiple selection
typedef	define a new type name	union	union type
unsigned	unsigned integer type	void	void type
volatile	volatile type	while	execute a loop

Identifiers

An identifier is a name used to identify a variable, function, or any other user-defined item. An identifier is a sequence of letters, digits, and underscores, and it must begin with a letter or an underscore.

Rules for defining identifiers

• An identifier must start with a letter (a to z or A to Z) or an underscore (_).

• After the first character, an identifier can contain any combination of letters, digits (0 to 9), and underscores.

• An identifier cannot be a keyword or a reserved identifier.

• There is no limit to the length of an identifier, but most compilers have a maximum limit of around 31 characters.

• An identifier can only contain ASCII characters.

Following are valid identifiers in C:

x
count
_temp
sum_of_numbers

The following are not valid identifiers in C because they do not start with a letter or an underscore:

1x (starts with a digit)
@count (starts with a special character)
temp! (ends with a special character)

tip

It is a good programming practice to choose descriptive and meaningful names for identifiers to make the code easy to understand and maintain.