Keywords are preserved words that have special meaning in C language. The meaning has already been described. These meaning cannot be changed. There are total 32 keywords in C language.
In C language identifiers are the names given to variables, constants, functions and user-define data. These identifier are defined against a set of rules.
Rules for an Identifier
- An Indetifier can only have alphanumeric characters( a-z , A-Z , 0-9 ) and underscore( _ ).
- The first character of an identifier can only contain alphabet( a-z , A-Z ) or underscore ( _ ).
- Identifiers are also case sensitive in C. For example name and Name are two different identifier in C.
- Keywords are not allowed to be used as Identifiers.
- No special characters, such as semicolon, period, whitespaces, slash or comma are permitted to be used in or as Identifier.
In C language characters are grouped into the following catagories,
- Letters(all alphabets a to z & A to Z).
- Digits (all digits 0 to 9).
- Special characters, ( such as colon
- White spaces.