Difference Between Keywords and Identifiers | Keywords vs Identifiers

By Anjnee Bhatnagar|Updated : May 13th, 2022

Difference Between Keywords and Identifiers: In C programming, keywords and identifiers play an important role as they are the basic building blocks of the language. We will explore the differences between keywords and identifiers in this article.

According to the C paradigm, there exist major differences between keywords and identifiers. A keyword in C has a predefined meaning, while an identifier is just a name assigned by the user or programmer to a memory, function, or a constant value. Before discussing the difference between keywords and identifiers, we will discuss each one in detail.

Table of Content

What is a Keyword in C?

Keywords are predefined reserved words present to the user in the C language. Any C program must have keywords present in it. In fact, a program in C begins with the keyword itself. The keyword is a type of C token.

In C, there are 32 reserved words or keywords present. Keywords are used in functions, blocks, loops, user-defined data structures, etc. The keywords are as follows: auto, default, float, register, struct, volatile, break, do, for, return, switch, while, char, else, if, signed, union, case, double, goto, short, typedef, const, enum, int, sizeof, unsigned, continue, extern, long, static, void.

What is an Identifier in C?

An identifier is just a name given to memory space or to a function for future reference in the program. An identifier does not have predefined meanings. They are user-defined names composed of letters and digits.

For an identifier to be valid, we need to follow the predefined rules to declare an identifier that is an identifier should only begin with a letter or an underscore and not by any digit. It cannot consist of any other special symbol other than letter, digits, and underscore.

Difference Between Keywords and Identifiers

Having discussed the meaning of each token type which is a keyword and an identifier, now we shall see the difference between keywords and identifiers. The differences are as follows:

Keyword vs Identifier



It should always be in lower case.

It can be in lower case or upper case.

It has a predefined meaning. They are reserved for use by the user.

It has no meaning attached to it. Usually, an identifier is a name provided by the user.

It can contain only the alphabet.

They can contain alphabets, digits, and underscores.

No special symbol is used.

Except for the underscore, no other special symbol is used.

It specifies the type of entity.

It gives a name to the type of entity.

Example: void, int, signed, etc.

Example: test, _abc, etc.


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  • There are various differences between keywords and identifiers. In terms of entity, a keyword specifies the type of entity. On the other hand, an identifier just provides a mere name to the type of entity.

  • In C programming, a token is defined as the smallest individual unit in a program. In C, we have five types of tokens. Every token holds a special functionality in itself. They are:

    ·      Keywords

    ·      Identifiers

    ·      Operators

    ·      Constants

    ·      Special symbols

  • In C, a keyword is also called a reserved word. A keyword has a predefined meaning. In C programming, there are 32 keywords present for user convenience. Some of the keywords are as follows: void, signed, int, volatile, main, getch, etc.

  • Keywords and identifiers in C are two different token types. A keyword has a predefined meaning and functionality. On the other hand, an identifier has no particular meaning. It is only provided by the user or programmer.

  • A keyword can only start in lowercase. All the keywords present in C are in lowercase and do not contain any special symbol. On the other hand, an identifier can start with lowercase, uppercase, or underscore. An Identifier allows only underscores and no other special symbols.

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