‘C ‘ Tokens:

In ‘C’ program the smallest individual units are called as tokens.
There are six types of tokens:
1. Identifiers.
2. Keywords
3. Constants
4. Strings
5. Operators

C’ character set: The ‘C’ character set denotes any alphabet, digit or special symbol used to represent information.
Following are the valid alphabets, numbers and special symbols allowed in C:

Alphabets                   A,B,………………………Z;a,b,……………………….z
Digits                           0,1,2,3,4,5,6,7,8,9
Special symbols         ! @ # % ^ & * ( ) _ – + = | \{ }, [ ], < > ” , ? / .

 

Identifiers:

A C identifier is a name used to identify a variable, function, or any other user-defined item.An identifier starts with a letter A to Z or a to z or an underscore _ followed by zero or more letters, underscores, and digits (0 to 9). C does not allow punctuation characters such as -, @, and % within identifiers. C is a case sensitive programming language. Thus, Demo and demo are two different identifiers in C.

Ex:Valid Identifiers: Foo _demo abc move_name a_123 myname50 _temp j a23b9 retVal
Invalid Identifiers: 1Demo a-123, demo@dss, a%b

Keywords:

Keywords are predefined tokens in C. These are also called as reserved words. Keywords have special meaning to
the C compiler. These words cannot be used for general purpose other than to which they are intended for.

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