Character Set, Keywords and Identifiers

Character Set
  The character set in C language can be grouped into the following categories.
   1. Letters
   2. Digits
   3. Special characters
   4. White spaces

White spaces are ignored by the compiler until they are a part of string constant.White space may be used to separate words, but are strictly prohibited while using between characters of keywords or identifiers.

C Character-set table

Special Characters

Keywords and Identifiers
  Every word in C language is a keyword or an identifier. Keywords in C language cannot be used as a variable name. They are specifically used by the compiler for own purpose and they serve as building blocks of a C program.
  
The following are the keyword set of C language.

Some compilers may have additional keywords.
  
Identifiers refers to the name of user-defined variables, array and functions. A variables should be essentially a sequence of letters and or digits and the variable name should begin with a character.
  
  Both uppercase and lowercase letters letters are permitted. The underscore character is also permitted in identifiers.