Keywords are the words whose meaning has already being explained to the C Compiler. Simply say, Keywords are Predefined words. The Keywords cannot be used as variable names because if we do so, we are trying to assign a new meaning to the keyword, which is not allowed by the compiler. Some compiler may allow, but it would be safer not to mix up the variable names and the keywords. The Keywords are also called ‘Reserved Words’.
There are only 32 keywords available in C.
auto double int
break else long
case enum register char extern return
const float short
continue for signed default goto sizeof
do if static
struct switch typedef
union unsigned void