In C language any user defined name is called identifier. This name may be variable
name, function name, goto label name, any other data type name like structure,
union, enum names or typedef name.
We need to follow following
rules while declaring variables (identifiers) in C program.
Rule 1: Name of identifier includes alphabets, digit and
underscore.
Example of Valid variable name:
india, add12, total_of_number etc.
Example of Invalid variable name:
show*marks, factorial#, avg value etc.
Rule 2: First
character of any identifier must be either alphabets or underscore.
Valid name: _total, _3, a_, etc.
Invalid name: 3_, 10_function, 12345 etc.
Rule 3: Name of identifier cannot be any keyword of c program.
Invalid name: int, float, char, if, else, for, switch,
etc
Rule 4: Name of identifier is case sensitive
i.e. num and Num are two different variables.
Rule 5: Only first 31
characters are significant of identifier name.
Example:
abcdefghijklmnopqrstuvwxyz123456aaa,
abcdefghijklmnopqrstuvwxyz123456bbb,
abcdefghijklmnopqrstuvwxyz123456cad
All three identifier name are
same because only first 31 characters has meaning. Rest has not any importance.
Rule 6: Must not contain white space.
Valid name: MyMarks
Invalid name: My Marks
* * * * *
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