C++ Identifiers

C++ identifiers are unique names assigned to identify variables, functions, classes, arrays, and other user-defined items in a program.

The examples of identifier in C++ are −

 int number = 10; string name = "John"; 

Here, number and name are identifiers for an integer and a string variable respectively.

Rules for Identifiers

• It must begin with a letter (uppercase "A-Z" or lowercase "a-z") or an underscore (_) but cannot start with a digit.
• After the first character, subsequent characters can be letters, digits (0-9), or underscores.
• Identifiers are case-sensitive (myVar and myvar are different).
• It cannot be a keyword (reserved word in C++), for example, int, bool, return, and while, etc.
• It must be unique within their namespace.
• Use meaningful names that reflect the purpose of the identifier (e.g, totalCount, calculateArea).
• In common practices, generally use camelCase or snake_case for readability.
• There is generally no strict limit on the length, but avoid long names as they make code harder to read and understand.

Types of Identifiers

Here are examples of identifiers in various cases −

1. Variable Identifiers

Variable identifiers are names given to variables in programming languages, which are used to identify reference data stored in those variables.

Here are a few examples of valid identifiers −

 int age; // 'age' is an identifier for an integer variable double salary; // 'salary' is an identifier for a double variable char initial_alpha; // 'initial_alpha' is an identifier for a character variable 

2. Constant Identifiers

Constant identifiers are names assigned to constants in programming, which represent fixed values that cannot be changed during the execution of a program.

Here is a simple example of a valid constant identifier −

 const int MAX_SIZE = 100; // 'MAX_SIZE' is an identifier for a constant 

3. Function Identifiers

Function identifiers are names assigned to functions in programming, which allow developers to define and call reusable blocks of code.

Some of the valid function identifiers are as follows −

 void calculateSum() { // 'calculateSum' is an identifier for a function // function implementation } int getValue() { // 'getValue' is another function identifier return 42; } 

4. Class Identifiers

Class identifiers are names assigned to classes in object-oriented programming which is used to define new data types that encapsulate attributes and behaviors associated with specific entities.

Here is a simple example of a valid class identifier −

 class Person { // 'Person' is an identifier for a class public: int age; string name; }; 

Example of Invalid Identifiers

Here are a few examples of invalid identifiers −

• 2ndValue (as it starts with a digit)
• first-name (it contains a hyphen)
• @username (begins with a special character)
• my variable (contains a space)
• float (uses a reserved keyword)