Keywords are preserved words that have special meaning in C language. The meaning of the keywords has already been described to the C compiler. These meaning cannot be changed. Thus, the keywords cannot be used as variable names because that would try to change the existing meaning of the keyword, which is not allowed. 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.
In C language characters are grouped into the following catagories,