Identifiers:
identifiers are nothing but the name given to variables, constants, functions and user-defined data.
Rules for an identifier:
- Keywords are not allowed to use as an identifier. Identifier may contains ( a-z, A-Z, 0-9 ) and underscore.
- The first character of an identifier must contain alphabet (a-z, AZ) or underscore( _ ).
- No special characters such as space semicolon, comma are permitted to use as an identifier.