• 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.
32 ANSI C Keywords
auto double int struct
break else long switch
case enum register typedef
const extern return union
char float short unsigned
continue for signed volatile
default goto sizeof void
do if static while


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 Identifier 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, white spaces, slash or comma are permitted to be used in or as Identifier.

Character set

In C language characters are grouped into the following categories,

  • Letters (all alphabets a to z & A to Z).
  • Digits (all digits 0 to 9).
  • Special characters ( such as colon :, semicolon ;, period ., underscore _, ampersand & etc).
  • White spaces.

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