C – Keywords and Identifiers3 min read

In this article you will learn about the Keywords, Identifiers and Tokens present in C. Let us first start with Character sets, knowing what are character sets then you will understand the rest in this article.
Let us begin.

Character sets:

In C Programming Character Sets refers to all the alphabets, letters and some special characters that are used in a program.


Keywords are defined as the reserved word that has a fixed meaning and those meanings cannot be changed. These are predefined by the program. There are a total of 32 keywords in ‘C’.

  • Keywords cannot be used as variables.
  • These are predefined by the compiler with special meaning.
  • There are 32 Keywords in c Programming.

For example: int temp;

The table below represent list of 32 Keyword in C Programming language:



Identifiers are nothing but the name assigned to the entities such as variables, functions in a program, Union, etc. Identifiers are user-defined in C Programming.

The name assigned to the entities is unique so that it can be identified during the execution of the program. Identifiers cannot be used as Keywords.

Example: int salary;, salary being identifier.

Rules for naming identifiers:

  • Identifiers are case-sensitive.
  • The first letter of identifiers must be a letter or underscore.
  • White spaces are not allowed.
  • There is no rule to decide the length of the name of identifiers.

Some valid and invalid identifiers:

What is Token in C?

The basic and smallest unit of a C program is called C tokens. These tokens are meaningful to the compiler. The compiler breaks the programs into the smallest unit that is the tokens and proceed with various compilation stages.

There are total six tokens in C Programming language.

token in C
Tokens in C


Keywords are reserved words whose meaning is predefined by the programming language specification. They convey some special meaning in programming and we must not use them for other purposes. They are basically a sequence of characters that have fixed to mean for example break, for, while, do-while, do, if, int, long, char.


Identifiers are names for entities in a C program, such as variables, arrays, functions, structures, unions, and labels. An identifier can be composed only of uppercase, lowercase letters, underscore and digits, but should only start with an alphabet or an underscore.


Operators are the mathematical symbols that are used to perform a mathematical operation on operands. These symbols tell the compiler to perform respective operations. An expression is formed by joining constants and variables in C programming.

Example: + symbol used to perform addition between two or more than two operands. Other symbols are: -, *, /, etc.


C programming defined string as a sequence or array of characters that are terminated by character ‘\0‘.
Example: str[]= “Strings Example”. These are enclosed within ” “.


From the name constant, we can say that these are fix values that are used in a program and its values remain the same during the entire execution of the program. Also, we cannot change the value in the middle of the program.

These constants may be any of the data-types present in C such as integer, float, boolean, etc.

Special Characters in C:

There are few special characters or special symbol in C programming language that has some special meaning and purposes. They are: [] () {}, ; * = #.

Example: [] (opening and closing brackets) is used for array elements reference.


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