What are C++ identifiers?

In C++, identifiers are the names given to various program elements like variables, functions, arrays, classes, and other user-defined items. Identifiers allow the programmer to refer to these elements in the code. Identifiers are essential because they provide a way to uniquely identify data or methods within the scope of a program.

Rules for Naming Identifiers:

1. Must Begin with a Letter or Underscore (_): The first character must be an alphabetic character (uppercase or lowercase) or an underscore. It cannot start with a digit.

   • Example: int age; is valid, but int 1stValue; is invalid.

2. May Contain Letters, Digits, and Underscores: After the first character, the identifier can contain letters, digits, or underscores.

   • Example: int value1;, char _name; are valid.

3. No Special Characters or Spaces Allowed: Identifiers cannot contain characters like @, #, $, %, or spaces.

   • Example: int my_value; is valid, but int my-value; is not.

4. Case-Sensitive: C++ is case-sensitive, meaning myVariable and myvariable would be considered different identifiers.

   • Example: int Count; int count; are two different variables.

5. Cannot Be a C++ Keyword: Keywords (like int, float, return, etc.) have predefined meanings in C++ and cannot be used as identifiers.

   • Example: int float; is invalid because float is a keyword.

Best Practices for Naming Identifiers:

• Use Meaningful Names: Identifiers should clearly reflect the purpose of the variable or function.
  • Example: int age; is more meaningful than int x;.
• Use Camel Case or Underscores: For multi-word identifiers, either use camelCase (myVariableName) or underscores (my_variable_name) to improve readability.

Example:

int score;         // Valid identifier
float _average;    // Valid identifier
char firstName;    // Valid identifier
int 1stValue;      // Invalid identifier (cannot start with a digit)

Conclusion:

C++ identifiers are used to name variables, functions, and other program elements. They must follow certain rules, including starting with a letter or underscore, containing no spaces or special characters, and being case-sensitive. Using meaningful and readable names is key to writing maintainable code.

Sources:

• GeeksforGeeks: Identifiers in C++
• Programiz: Identifiers in C++