C Foundation

What is C? C Compiler Installation C Extensions C Compiler C Interpreter C Program Structure

C Basics

C Keywords C Data Types C Identifiers C Variables C Constant C Escape Sequences C Constant and Volatile C Typecast


What is Operator C Comma Operator C Arithmetic Operators C Relational Operators C Logical Operators C Bitwise Operators C Conditional Operators C : : Operator C Operator Priority

Basic IO's

Basic IO's C Formatted Functions C Unformatted Functions C Common Functions

Control Statements

What is Control Statement C if Statement C if else Statement C Nested if Statement C Else if Statement C Break Statement C Continue Statement C Switch Statement C Goto Statement


What is Control Loop C for Loop C Nested for Loop C while Loop C Nested while Loop C do while Loop C Nested do while loop


What is Function C User Defined Functions C Recursion C Passing Parameters


Scope C Local Scope C Global Scope

Storage Classes

What is Storage Class C Auto C Extern C Static C Register


What is Array C One Dimensional Array C Two Dimensional Array C Multi Dimensional Array C Arrays Of Strings


What is String C String Functions


What is Pointer C Pointers Arithmetic C Pointer to Pointer C Pointers and Arrays C Pointers and Strings C Pointer to Functions Void Pointers Null Pointers C Null and Void Pointer


What is Structure C Struct within Struct C Array within Structure C Pointer to Structure C Structure and Function C Enum C Bitfield Structure C Type def


What is Union


What is File C read a file C write a file C File Handling C Error Handling C Low Level Disk I/O C Other file functions

Memory Allocation

What is Memory Allocation C Malloc() C Calloc() C Free() C Realloc() C Coreleft()

C Reference

All ASCII Code Basic C Questions

C Interview

C Interview Sets All Star Patterns All Number Patterns All Alphabet Patterns All Series Patterns
The ones who are crazy enough to think they can change the world are the ones who do.
- Steve Jobs

C Identifiers

What is Identifier?

An identifier is a name that identifies unique things. here things may be a person, object, idea or anything. The following diagram clearly represents the concept of identifier.

identifiers in c

Identifiers In C

  • Identifier as the name suggest are used identify elements in C Programming.
  • Identifiers is a sequence of characters and digits created by a programmer to identify various program elements.
  • Identifiers are the names of variables, arrays, functions, structure.
  • C Programming language is case-sensitive, so uppercase, lowercase, camelcase letters will be treated differently.
  • Here is some example are: firstname, FIRSTNAME, FirstName will be treated differently.
  • But in general practice the lowercase and CamelCase letters can be used as a variable name, function name, array name and structure name, while UPPERCASE letters are used for symbolic constants.
  • Programmer can use underscores  _  in between identifiers. e.g.) first_name.

Identifier C Program

#include <stdio.h>
int main()
int number = 25;
int Number = 47;
printf("The number is %d ",number);
printf("\nThe Number is %d ",Number);
return 0;
  • The number is 25
  • The Number is 47


number and Number are two different variable (Identifiers) with same meaning.

Identifiers Rules For Declaration

  • First character must be a letter or underscore _.
  • Characters in identifiers are limited up to 31 in ANSI C compiler(it may vary).
  • Blankspaces and commas are not allowed within an Identifier.
  • Identifiers should not be starts with a digit.
  • Identifier name should not be the keyword.
  • Identifiers must be short and meaningful.

Did You Know?

Once identifier is declared under any datatype it cannot be redeclared even my its current datatype itself.

Program For Verification

#include <stdio.h>
int main()
int number = 25;
int Number;
int Number = 47.00;
printf("The number is %d ",number);
printf("\nThe Number is %d ",Number);
return 0;


The above program will cause error as identifier Number is redeclared.

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