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C++ Identifiers - GeeksforGeeks

Last Updated : 23 Jul, 2025

In C++ programming language, identifiers are the unique names assigned to variables, functions, classes, structs, or other entities within the program. Let's take a look at an example:

// Creating a variable
int val = 10;

// Creating a function
void func() {}

In the above code, the words val and func are identifiers. Basically, everything named by a programmer is an identifier and is used to refer to the entity later in the program.

We can use any word as an identifier as long as it follows the following rules:

• An identifier can consist of letters (A-Z or a-z), digits (0-9), and underscores (_). Special characters and spaces are not allowed.
• An identifier can only begin with a letter or an underscore only.
• C++ has reserved keywords that cannot be used as identifiers since they have predefined meanings in the language. For example, int cannot be used as an identifier as it already has some predefined meaning in C++. Attempting to use these as identifiers will result in a compilation error.
• Identifier must be unique in its namespace.

Additionally, C++ is a case-sensitive language so the identifier such as Num and num are treated as different. The below images show some valid and invalid C++ identifiers.

To know more about identifiers naming rules, refer to this article – Naming Convention in C++

In this example, we have used the identifiers by following the guidelines and we use identifiers to name a class, function, integer data type, etc. If you are not aware of functions and classes in C++ then don’t worry, you will learn them soon. The below code is run successfully which means we named them correctly.

#include <iostream>
using namespace std;

// Here Car identifier is used to refer to below class
class Car {
    string Brand;
    string model;
    int year;
};

// getSum identifier is used to call the below
// function
void getSum(int a, int b) {
    int _sum = a + b;
    cout << "The sum is: " << _sum;
}

int main() {
  
    // Identifiers used as variable names
    int studentAge = 20;
    double accountBalance = 1000.50;
    string student_Name = "Karan";

    getSum(2, 10);

    return 0;
}

Naming conventions are not the rules enforced by C++ language but are suggestions for naming variables by the programming community for easier understanding. Some of the naming conventions are as follows:

For Variables:

• Use camelCase (for constants, you can use UPPER_SNAKE_CASE)
• Start with lowercase alphabet.
• Use descriptive, meaningful names.
• For example, frequencyCount, personName

For Functions:

• Use camelCase.
• Use Verb or verb phrases for naming.
• For example, getName(), countFrequency(), etc.

For Classes:

• Use PascalCase
• Use Nouns or noun phrases for naming.
• For example, Car, Person, etc

Once again, above are some suggestions for naming identifiers do not rule. They also depend on the project guidelines you are working on and your preferences.

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