Character Set used in C language is basically divided into 3 section.
Upper Case: A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
Lower Case: a b c d e f g h I j k l m n o p q r s t u v w x y z
Integer : 0 1 2 3 4 5 6 7 8 9
C has reserved some keywords for its own use.See the below table.
These all keyword has some standard meaning defined in standard library so it can’t be used for another purpose in the program by the user.
The identifier is a term used for the name. In ‘C’ language, Identifier is used for the variable name, function name and structure tags etc.
Key points remember for an Identifier:
— Identifier name can use all 52 alphabets(upper and lower case), integers and only one symbol _(Underscore).
— The first character of the identifier should be always from alphabets or _(Underscore)
— Identifier name should be less than 31 characters.(See Table example 7 ).
— Identifier name must not be in C reserved keyword.(See Table example 8 ).
See the below table for some example –