Identifiers
The identifiers are user defined names in programs for assigning names to variables, arrays and functions. The identifiers are made up of letters(uppercase and lowercase), digits and underscore. The C is case sensitive and hence the uppercase and lowercase letters are treated as different. For example, max and Max, are not same.
Normally, the lowercase letters are used in identifiers, but is not the limitation as uppercase can also be used. The keyword listed in the previous section has special meaning to C and can not be used as identifiers.