Identifiers and Keywords in C Language
As we have learned in earlier that tokens are the smallest individual unit of a C program. It is classified into identifiers, keywords, constants, string literals, operators, special symbols.
Identifiers
Identifiers are the name that is used to identify a variables, functions, constants and the user defined items.
*) The identifier can start with a letter between 'A' to 'Z', 'a' to 'z' and underscore('_').
*) No space and special symbols are allowed between the identifier.
*) The identifier cannot be a keyword.
*) The identifiers are case sensitive. Example the variables 'age' and 'Age' are considered as two different identifiers.
Example for valid identifiers
int age;
int age1;
The age and age1 are valid identifiers.
Example for invalid identifier
int 1age;
int #age;
The 1age and #age are not valid identifiers, since it does not follow the above rules.
Keywords
The keywords are the reserved words in C language. C language contains keywords which are described in C compiler. So these keywords cannot be used as the variable name.
| auto | else | long | switch |
|---|---|---|---|
| break | enum | register | typedef |
| case | extern | return | union |
| char | float | short | unsigned |
| const | for | signed | void |
| continue | goto | sizeof | volatile |
| default | if | static | while |
| do | int | struct | double |
If we try to create a variable with any of the above keywords, it will throw an error.