Identifiers - C programming language

Identifiers

Identifers are the names given to a program elements such as variables , arrays, and functions. Identifiers must be unique. They are created to give unique names to a entity to identify it during the execute of the program . Identifiers names must be different from keywords . You cannot use int as an identifiers because int is a keyword.

 Rules of Identifiers

• It can not have special character except the underscore "_".
• It can not be a keyword.
• It can not have spaces in between.
• It must begin with a alphabates or an underscore. 
• C is also a case sensitive language so here "Class" & "class" both are different.
• It can not certain more then 31 characters.

Example of valid identifiers

total, sum, average, _m _, sum_1, etc. 

Example of invalid identifiers

2sum (starts with a numerical digit) 

int (reserved word) 

char (reserved word) 

m+n (special character, i.e., '+')