Pascal Tutorial 5A - Enumerated Types

5A - Enumerated Types

You can declare your own ordinal data types. You do this in the type section of your program:
type datatypeidentifier = typespecification;

One way to do it is by creating an enumerated type. An enumerated type specification has the syntax:
(identifier1, identifier2, ... identifiern)
For example, if you wanted to declare the months of the year, you would do a type:

   type
      MonthType = (January, February, March, April, May, June,
                   July, August, September, October, November,
                   December);

You can then declare a variable:

   var
      Month : MonthType;

You can assign any enumerated value to the variable:

   Month := January;

All the ordinal functions are valid on the enumerated type. ord(January) = 0, and ord(December) = 11.

A few restrictions apply, though: enumerated types are internal to a program -- they can neither be read from nor written to a text file. You must read data in and convert it to an enumerated type. Also, the idenfier used in the type (such as January) cannot be used in another type.

The main purpose of an enumerated type is to allow you, the programmer, to refer to meaningful names for data. Sometimes, when the built in data types don't suffice, it is easier to use an enumerated type than to keep the inputted data as a string.