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C++ Identifiers

C++ identifiers in a program are used to refer to the name of the variables, functions, arrays, or other user-defined data types created by the programmer. They are the basic requirement of any language. Every language has its own rules for naming the identifiers.

In short, Type of Identifiers are

  • Constants

  • Variables

  • Functions

  • Labels

  • Defined data types

Constant – In Cpp, constant is what ?

Which is Constant ?

Who remains constant throughout the program

Example- Suppose int a=5;

Let’s see a simple program to implement the constant

  • #include<iostream>

  • using namespace std;

  • int main()

  • {

  • int a=5;

  • cout<<a;

  • }

Output –


So, the value of “a” is going to remain same throughout the program

Variable – What is a variable ?

Whose value vary throughout the program

Example – for(int i=0; i<5; i++)

Here i is incrementing so it is a variable.

Let’s see a simple program to implement variable

  • #include<iostream>

  • using namespace std;

  • int main()

  • {

  • for(int a=0; a<5; a++)

  • {

  • cout<<a<<endl;

  • }

  • }

Output –






There are some rules in C++ language to define an identifier

· Only alphabets, characters, digits & underscores are allowed.

· The identifier name must not start with a digit ex 0 to 9. First letter must be alphabetical

· Uppercase & Lowercase letters are different in C++ language

· A keyword can’t be used as variable name

Example of Valid Identifiers





Example of Invalid Identifiers

test-1 //contains special char – Not Allowed

2test //first letter is a digit – Not Allowed

while //Keyword in C++ - Not Allowed

To Avoid confusion between identifiers & keywords let’s see quick differences between them

Keywords are the reserved words predefined in the language but Identifiers are words we used to define a constant or variable.

S. No.




Identifiers are the names defined by programmers/coders/developers to declare a variable during programming/coding.

Keywords are the reserved words made by compiler developer or we can say they are pre-defined in a language.


Contains letters, numbers, underscore

Contain only letters


Both lowercase & uppercase letters are allowed

Only lowercase tutorials are allowed


Used to identify the name of variable

Used to specify the type of entity.


Use of underscore is allowed

Use of Underscore is not allowed


The starting letter of underscore is small alphabet, large alphabet or underscore.

Only Lowercase letter is allowed.


Further classification of two types – internal & external

No further classification


Examples – test, result, sum, a..

Examples – if, else, while, for, break…

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