Identifier

                                                              Identifier
Identifier is a name given to various program element such as variable name,function name,array name etc.

• First letter must be an alphabet or underscore
• We can use use a-z,A-Z,0-9,underscore in identifiers . 
•  We cannot use keyword as identifier because they are reserved words which have predefined meaning.
• We cannot use same name in different case both have predefined meaning 
• Valid or invalid identifiers:-

         cguruankit             valid      

         123cguruanki        invalid

          _cguruankit          valid

         Num cguruankit    invalid
         int 2a;                   invalid
         int a_2;                 valid

         int a,A;                 valid
         int a,a;                  invalid