Every C word is classified as either as keyword or an identifier.
Keywords : keywords are reserved words that have predefined standard meaning in C i.e., the meaning is already defined.
- Keywords can not be used as identifiers.
- Keywords depends on th compiler used for compiling the program.
- All keywords must be written in lowercase letters.
- The meanings of the keywords cannot be changed.
- Keywords server as basic building blocks for program statements.
- In ANSI C, there are 32 keywords.
int a = 20; Here int is a keyword.
while(i < 10); Here while is a keyword.
Following are some of the standard keywords.
Identifiers : Identifiers refer to the names of variables, functions and arrays, which are defined by the users.
Rules for Identifiers :
- Identifiers consist of a sequence of letters or alphabets(a to z or A to Z), digits (0 to 9) or underscore(_)
- No special symbols are allowed except underscore.
- The first character always must be an alphabet or underscore, but it should not be a digit.
- Both uppercase and lowercase letters are permitted.
- Length of an identifier depends on he version and the computer used.
- Identifier length is up to 8 characters for 16 bit machine and up to 31 characters for 32 bit machine.
- No two successive undercovers are allowed.
- Keywords cannot be used as identifiers.
Mo commas or blanks are allowed with in variable name.
Valid Identifiers : volume, y12, _sum, pop_e_89.
Invalid Identifers : 2abc, reg.no, "z", pop_ _e89, 3rd