Identifiers

Identifiers: A name or identifier in C can be anything from a single letter to a word. Identifiers are the names given to program elements such as variables, function names, array names and structure names. Once a type or value is assigned to an identifier, it cannot be changed during the execution of the program. For example: if an integer variable named as 'x' then 'x' will always remain an integer variable which can hold only integer or numeric value.

Rules of identifier: 1) an identifier must be unique in a program.

2) An identifier can contain only alphabets, digits and underscore. No any other symbol can be used.

3) The identifier must begin with a letter or an underscore.

4) An identifier must not start with a digit.

5) C language is a case sensitive language. It means upper case and lower case letters are different identifier.

6) An identifier must not contain any white space. The white space includes tab, spacebar and new line.

7) It can’t be a C language keyword or reserve word. As we know that C is a case sensitive language and we can use different case of keywords as identifier.

8) An identifier cannot use a symbol in naming.

9) Some valid examples are: a, box, tab10, roll_no, Roll_no, _abc, For.

10) Some invalid examples are: 10tab, for, ab$c, roll no.