What is keyword and identifier ? What are the rules for identifier?

Last updated on June 13th, 2020 at 08:25 pm


Keywords have fixed meanings and these meanings can not be changed. There are 32 keywords. Some compiler may use additional keywords that must be identified from the C manual. Keywords serve as basic building block for a program statement.

Such as, autobreakdouble etc. All keyword must be written in lowercase.


The names of variables, functions and arrays are identifiers. These are user-defined names and consist of a sequence of letters and digits. Such as, my_num, _ton etc.

Rules for identifier:

  1. Must consist of only letters, digits and underscores.
  2. First character must be an alphabet or underscore.
  3. Only first 31 characters are significant.
  4. Can not use a keyword.
  5. Must not contain white spaces.