Identifiers in C

Identifier is used to name various elements of program such as variables, constants, functions, arrays, functions etc. An identifier is a word consisting of sequence of Letters, Digits or _(underscore).

Rules to Name identifiers are

1. The variables must always begin with a letter or underscore as the first character.

2. The following letters can be any number of letters, digits or underscore.

3. Maximum length of any identifier is 31 characters for external names or 63 characters for local names.

4. Identifiers are case sensitive. Ex. Rate and RaTe are two different identifiers.

5. The variable name should not be a keyword.

6. No special symbols are allowed except underscore.

Examples:

Valid identifiers:

Sum
roll_no
_name
sum_of_digits
avg_of_3_nums

Invalid Identifiers and reason for invalid:

$roll_no - Name doesn‟t begin with either letter or underscore
for - keyword is used as name
sum,1 - special symbol comma is not allowed
3_factorial - name begins with digit as first letter