Types, Variables, and Constants
All classes and interfaces you create in .NET are considered types. That is, they define a specific type of data. The underlying classes in the .NET Framework are also all strong types. In fact, the .NET languages of both C# and VB are based on strongly typed objects. This means when you define a variable you create an instance of a strongly typed class. The .NET runtime can then rely on this type information for handling casting, comparisons, and other rules.
There are a number of built-in types (classes) that are used for common programming needs. These built-in types are referred to as data types and represent things such as a string of characters or a numeric value. You work with these data types ...