Identifiers in c

the first character should be alphabet or underscore
we can use _ (underscore) for starting alphabet
succeeding characters can be digits or alphabets
Only first 31 characters are significant.
A max 31 characters should be used.
Uppercase and lowercase identifiers are different
keywords are not used as identifiers
now two successive underscores are allowed
no special characters or symbols are allowed except underscore

Identifiers are names given to variables, functions, and arrays. There are some rules(above) for identifiers.these are user-defined names

Valid examples

var
_ex
_ri67
z

Invalid examples

:xe
68iy
my var
#ty
6.3