Identifiers and keywords in C

June 23, 2025

Identifiers and Keywords

In this section, we will learn about the keywords, reversed words in the C programming tat are the part of the syntax. also we will learn about the identifiers and how to name them.

Keywords int,double ,struct,switch etc.

Identifiers test,count, high, high_speed etc.

now we will study about identifiers and keywords in detail. we will see, how many keywords is there in C programming and all the rule for the select identifiers.

Keywords in C

Keywords are predefined, reserved words used in programming that have special meanings to compiler. Each keyword is meant to perform a specific function in a C program. Since keywords are referred name for compiler, they can not be used as variable name.

There are fixed number of Keyword in C programming language and every Keyword serve as a building block for program statements.

There are total 32 keywords in C keywords are written in lowercase letters..

Keywords table

Following table represents the keywords in C. Here is a list of some identifiers given below

C Language Keywords

Keyword

auto

break

case

char

const

continue

default

Keyword

else

enum

double

float

for

goto

int

Keyword

long

return

short

signed

sizeof

static

struct

Keyword

switch

typedef

union

unsigned

void

volatile

while

_Packed

Tokens in C

Variables in C

Data Types in C

Size of data types in C

Enums in C

Identifiers in C

Each program elements in a C program are given a name called identifiers. Name given to identity variable, functions and arrays are examples for identifiers.

identifiers must be unique. they are created to give a unique name to an entity to identify it during the execution of the program.

for example

 1 int square
 2 double balance 
 3 function add()

Here, square , balance and add() are identifier. there are one thing that you should remember, identifier names must be different from keywords. you cannot use int as an identifier because int is keyword.

Rule for an identifier

An identifier can only have alphanumeric characters (a-z, A-Z, 0-9) and underscore (_).
The first character of an identifier can also contain alphabet (a-z, A-Z).
Identifiers are also case sensitive in C. For example name and Name are two different identifiers in C.
Keywords are not allowed to be used as identifiers.
No special character, such as semicolon, period, white spaces, slash or comma are permitted to be used in or as identifiers.

Difference between Keyword and Identifier

Basic

Keyword: Keywords are the reserved words of a language.

Identifier: Identifiers are the user-defined names of variables, functions, and labels.

Use

Keyword: Specify the type/kind of entity.

Identifier: Identify the name of a particular entity.

Format

Keyword: Consider only letters.

Identifier: Consider letters, underscores, and digits.

Case

Keyword: Use only lowercase.

Identifier: Lowercase and uppercase, both are allowed.

Symbol

Keyword: No special symbol or punctuation is used.

Identifier: No punctuation or special symbol except underscore is used.

Classifications

Keyword: Keyword not further classified.

Identifier: Identifiers are classified into external and internal names.

Starting Letter

Keyword: It always starts with a lowercase letter.

Identifier: First character can be uppercase, lowercase, or underscore.

Conclusion

To sum up, keywords and identifiers are basic but important parts of C programming.

Keywords are reserved words like int, if, and return that have special meanings and can’t be used for anything else.
Identifiers are the names we give to variables, functions, and other elements we create.
They must follow certain rules and can’t be the same as keywords.
Knowing the difference helps avoid errors and write clear, working programs.
If you’re learning C, start by practicing how to name things correctly and understand what each keyword does. It builds a strong base for coding ahead.

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Identifiers and keywords in C