Define the Keywords of c language?

C keeps a small set of keywords for its personal use. These keywords can't be used as identifiers in the program. Here is the list of keywords used in Standard C that you will notice that none of them use upper-case letters.

auto                 double              int                   struct

break               else                  long                 switch

case                 enum               register            typedef

char                 extern              return              union

const                float                 short              unsigned

continue          for                   signed              void

default           goto                 sizeof               volatile

do                    if                    static              while

Each one keyword must be written in lower case. Ever since upper case and lower case characters are not equivalent. It is possible to use upper case keyword as an identifier.