Identifiers are user defined words and refer to the names of variable, function arrays, structure,etc. It consist of a sequence of letters and digits with a letter as a first character. Both uppercase letters and lowercase letters are permitted, although lowercase letters are commonly used.

Rules of Identifiers:

  1. First character must be an alphabet or underscore.
  2. Must consist only uppercase and lowercase letters, digits and underscore sign.
  3. A keyword cannot be use.
  4. Only implementations 31 character, that are recognize by ANSI standard.
  5. Most not contain white space.

Some examples of valid identifier:-

a     age     NAME     _space     new1     white-space

Some example of invalid identifier:-

1new     First character must be an alphabet or underscore.
int         A keyword cannot be use.
note#   # is a special character.
no 1    blank space is not permitted.