Identifier in C++ |

 the name of a variable , function , class , or other entity in c++ is called an identifier.

rules :  

•  The identifier can not be a keyword . Keywords are reserved .
• The identifier can only be composed letters, number , and the underscore character . that means the name can not contains symbols nor 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 letter .