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.