Notes – Identifier & Keywords in C++

In C++, identifiers and keywords are basic elements of any program.

• Identifiers are the names used to identify variables, functions, classes, arrays, etc.
• Keywords are reserved words in the language that have special meaning and cannot be used as identifiers.

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What Is an Identifier?

An identifier is the name given by the programmer to a variable, function, class, or object.

Examples:

int age;
float totalMarks;
void printData() {}

In the above code:

• age, totalMarks, and printData are identifiers

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Rules for Naming Identifiers

Rule	Description
Must begin with a letter (A–Z, a–z) or underscore _
Can include letters, digits (0–9), and underscores
Cannot start with a digit
Cannot use C++ keywords as identifiers
Case-sensitive — Score and score are different
Avoid special characters like @, $, % (not allowed)

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Valid vs Invalid Identifiers

Valid Identifiers	Invalid Identifiers	Reason
totalMarks	2ndPlace	Cannot start with a digit
employee_name	float	float is a keyword
_value123	student-score	Hyphen not allowed

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Tips for Writing Good Identifiers

• Use meaningful names (totalAmount instead of ta)
• Use consistent naming styles like camelCase or snake_case
• Avoid single-letter names (unless in loops like i, j)

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What Are Keywords?

Keywords are predefined and reserved words in C++.

They have special meanings and cannot be used as variable or function names.

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Common C++ Keywords

int       float     return     class     public  
private   if        else       while     for  
break     continue  void       this      new  
delete    try       catch      throw     const

C++ has over 60 keywords. You can’t use any of them as identifiers.