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5.2. Using types other than the simple types

One approach to writing a program is to identify the real-world objects (of the problem) that you need to represent in the program. Each real-world object can be in a number of states (i.e., may possess one of a number of values) and has a set of operations that can be performed on it.

Some of these real-world objects can be represented in a program by variables each of which is declared to be one of the simple types. For example, if our problem needs to represent the number of students in a lecture theatre, we can use an Integer in a VB.NET program in order to represent this real-world object. Or we might use a variable of type Double in order to represent the temperature of the air outside.

However, there are many real-world objects that cannot be represented in a VB.NET program by a value that is of a simple type. For example, we might want to represent a date in history, a point in two-dimensional space, the ISBN of a book, an e-mail address, the URL of a WWW page, and so on.

In most programming languages, a programmer can introduce new types to model these real-world objects. One way of doing this in a .NET language is to introduce a class declaration: we could introduce a class declaration for each of these classes of real-world objects.

However, we need not get into the details of writing class declarations straightaway: any .NET language can use any of the large number of classes defined in the Framework Class Library: maybe the FCL has a class that we can use.