Keywords is defined as the pre-defined and reserved words in a programming language. Every keyword is means to perform a specific function in a program and keyword has its own functionality so keywords are referred names for a compiler, they cannot be used as variable names.we are trying to assign a new meaning to the keyword which is not allowed and cannot be used as the variable names. You cannot redefine keywords. There are 32 keywords they are follows
| auto | double | int | struct |
| break | else | long | switch |
| case | enum | register | typedef |
| char | extern | return | union |
| const | float | short | unsigned |
| continue | for | signed | void |
| default | goto | sizeof | volatile |
| do | if | static | while |
The identifiers are a collection of alphanumeric characters that start with an alphabetical character or an underscore, which are used to represent different programming elements such as variables, functions, arrays, structures, unions, labels, etc They are user-defined names consisting of an arbitrarily long sequence of letters and digits with a letter or the underscore(_) as a first character. It must differ in spelling and case from any keywords. Once you declared the identifier, you can use it in later program statements to refer to the associated value. A spcific kind of identifier, called a statement label, can be used in goto statements.