Every word in C++ language is a keyword or an identifier. Keywords in C++ language cannot be used as a variable name. They are specifically used by the compiler for its own purpose and they serve as building blocks of a C++ program. C++ language has some reserve words which are called keywords of C++ language. These are the part of the C++ Tokens.
There are 63 keywords currently defined for Standard C++. These are shown in Table. Together with the formal C++ syntax, they form the C++ programming language. Also, early versions of C++ defined the overload keyword, but it is obsolete. Keep in mind that C++ is a case-sensitive language and it requires that all keywords be in lowercase.
The name of a variable, function, class, or other entity in C++ is called an identifier. C++ gives you a lot of flexibility to name identifiers as you wish. However, thereare a few rules that must be followed when naming identifiers:
• An identifier that cannot be used as a variable name is a reserved word.
• The identifier can only be composed of letters, numbers, and the underscore character. That means the name can not contains no symbols (except the underscore) or whitespace.
• The identifier must begin with a letter or an underscore. It can not start with a number.
• C++ distinguishes between lower and upper case letters nvalue is different than nValue is different than NVALUE.