Identifiers are the programmer defined elements like the name of variables, functions arrays, structures etc, They are the fundamental requirement of any language.
These are token which is composed of a sequence of letters, digits, and underscore ( _ ). Every language has its own rules for naming identifiers. Identifiers are used to give unique names to different objects in the program.
Rules For Naming Identifiers In C
- An identifier is any combination of alphabets, digits or underscore.
- The first character in the identifier name must be an alphabet and not a digit but after that, any digit may follow.
- No blank (white space) are allowed within an identifier.
- No special symbols other than underscore(as in stn_name) can be used in an identifier.
- A maximum length of an identifier is compiler dependent. Originally it was 8 characters. ANSI C permits 31 characters in identifiers.
- Upper case and lower case letters are distinct.
- A keyword cannot be used as an identifier.
- Identifier name should be unique.
- The Same Identifier cannot be used again to give the name to another object.
C Identifier Example
Following are some possible examples of identifiers to represent length of box;