Identifiers in C

An identifier is a user-defined name used to identify variables, functions, arrays, structures, and other program elements in C.

In simple terms, identifiers are the names given by programmers to different components of a program.

Examples

Variable Identifier / Function Identifier

int age = 25;

void display() {
}

Here, age is an identifier.

Here, display is an identifier.

Rules for Naming Identifiers

A valid identifier in C must follow these rules:

• Can contain letters (A-Z, a-z), digits (0-9), and underscore (_).

• Must begin with a letter or underscore.

• Cannot start with a digit.

• Identifiers are case-sensitive.

• Cannot use C keywords as identifiers.

• Special characters such as @, #, $, %, - are not allowed.

Valid Identifiers

age
studentName
_count
totalMarks
student1

Invalid Identifiers

1student
user-name
user@name
return
int

Example: Identifier as a Variable

#include <stdio.h>

int main() {

    int marks;
    marks = 90;

    printf("%d", marks);

    return 0;
}

Output

90

In this example, marks is the identifier.

Example: Identifier as a Function

#include <stdio.h>

int sum(int a, int b) {
    return a + b;
}

int main() {

    printf("%d", sum(10, 20));

    return 0;
}

Output

30

In this example, sum is the identifier.

Naming Conventions

Although not mandatory, these conventions improve code readability.

Variables

Use camelCase naming.

int studentAge;
int totalMarks;
int employeeCount;

Constants

Use UPPER_SNAKE_CASE naming.

#define MAX_SIZE 100
#define PI 3.14

Functions

Use camelCase and meaningful action names.

getName();
calculateSalary();
countFrequency();

Structures

Use PascalCase naming.

struct Student;
struct Employee;
struct Car;

Using Keywords as Identifiers

Keywords are reserved words in C and cannot be used as identifiers.

Incorrect Example

#include <stdio.h>

int main() {

    int const = 90;

    return 0;
}

Error

error: expected identifier or '(' before '=' token

The error occurs because const is a C keyword and cannot be used as an identifier.

Common C Keywords

int
char
float
double
if
else
for
while
switch
case
break
continue
return
const
void

Key Points

• An identifier is a user-defined name.

• Used for variables, functions, arrays, structures, and other program elements.

• Must start with a letter or underscore.

• Cannot start with a digit.

• Cannot be a keyword.

• Identifiers are case-sensitive.

• Meaningful names make code easier to read and maintain.