Identifiers in C

Identifiers are the user-defined names (with a sequence of letters and digits) given to the variables, arrays, functions, structures, unions etc.

For example: In terms of computer, it uses the range of addresses to identify the data. But as a programmer, we can't get those addresses before program execution. so rather than using addresses, we use identifiers. 

Rules of identifiers :

In order to remove the ambiguity during the compilation process, C creators imposed a set of rules on identifiers. They are :

• The first character must start with a letter (A to Z) or (a to z) or with an underscore (_).
• An identifier should contain only letters (A to Z) or (a-z) or digits (0 to 9) or an underscore (_).
• Identifers are case-sensitive i.e  "EXAMPLE", "example", "Example", "eXample" are four different identifiers.
• Identifiers should not contain any 'special characters' & 'white space characters' except underscore.

Special characters:

Whitespace characters:

• Keywords are not allowed to use as identifiers because keywords are the reserved words.

Valid identifiers:

• _dataoverride
• c_tutorials1
• jamesbond007
• Final__Example

Invalid identifiers:

• 123example
• @example2
• data override
• float (It is invalid because the float is a keyword)

Note:

Refer "page 192  section A2.3  Identifiers" in "The C programming language by Dennis M Ritchie & Brian W. Kernighan". This book was written by creators of C.

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