Identifiers in c programming language

•  What are Identifiers in C?

Identifiers are the names given to program elements in C.

They are used to identify variables, functions, arrays, structures, unions, and labels.

👉 Simply: An identifier is a name used to identify something in a program.

• Examples of Identifiers

C

int number;

float total_marks;

void calculateSum();

• Here:

number → variable identifier

total_marks → variable identifier

calculateSum → function identifier

• Rules for Naming Identifiers in C

An identifier must follow these rules:

1.Only alphabets, digits, and underscore (_) are allowed

✅ total_marks

❌ total-marks

2.First character must be a letter or underscore

✅ _count, sum

❌ 1sum

3.Cannot use keywords as identifiers

❌ int, float, return

(These are reserved words)

4.No spaces allowed

❌ total marks

✅ total_marks

5.Case-sensitive

Sum and sum are different identifiers

6.Length

C allows long identifiers, but first 31 characters are significant (for many compilers)

👉Valid and Invalid Identifiers😀

Valid Identifiers

C

marks

_total

student1

sum_of_numbers

• Invalid Identifiers

C

1student // starts with digit

total-marks // special character

float // keyword

total marks // space

• Types of Identifiers in C

1. Variable Identifiers

Used to name variables.

C

int age;

float salary;

2. Function Identifiers

Used to name functions.

C

void display();

int add(int a, int b);

3. Array Identifiers

Used to name arrays.

C

int marks[5];

4. Structure Identifiers

Used to name structures

C

struct Student {

    int roll;

    char name[20];

};

5. Label Identifiers

Used with goto statement.

C

start:

printf("Hello");

💥 Identifier vs Keyword (Difference)

       Identifier                      Keyword

• User-defined name      Pre-defined by C
• Can be changed            Cannot be changed
• Example: total              Example: int