Keywords are the reserved words in C++ that have a predefined meaning. They form an important part of C++ syntax and cannot be used as names for variables, classes, or functions.

What makes a keyword special

• Keywords are predefined and reserved by the language.
• Each keyword has a special meaning in C++.
• Keywords are always written in lowercase.
• Keywords cannot be used as identifiers.

Examples of C++ keywords

• class
• while
• for
• template
• virtual
• public
• private
• return

Rules for identifiers

Identifiers are the names you assign to variables, constants, functions, classes, and other entities. They must follow C++ naming rules and must not match reserved keywords.

• The first character must be a letter or underscore.
• Identifiers cannot start with digits, but they may contain digits later.
• Whitespace cannot be included.
• Identifiers are case sensitive.
• Avoid starting with double underscores or underscore followed by uppercase (reserved for compiler/library).

Valid and invalid examples

• Valid: myVariable, MAX_SIZE, _count, calculateSum
• Invalid: 123variable, my-variable, my variable