Identifiers are user-defined tokens used to name variables, functions, etc. An identifier consists of a sequence of letters and digits. Underscore is also used. However, the first character of the identifier should a letter or an underscore. Though there is logically no restriction on the length of the number of characters in an identifier, however for some compilers only 31 characters are significant to differentiate between 2 or more identifiers. It should be noted that identifier is case sensitive. This means an identifier “test” is different from another identifier “teSt”. Table-1 shows some valid and invalid identifiers along with the reason.
Table – 1: Examples of some valid and invalid identifiers