A structure is a user-defined data type that allows a single variable to store more than one type of data. In Visual Basic 6, structures were actually called user-defined types. The structure object has been improved in VB.NET, however, because VB.NET structures can contain both data and subprocedures to operate on those data. Structures are very common in form to classes, though they have several limitations that restrict their use to solve object-oriented programming problems. Because they are similar in form to classes, structures provide an excellent introduction to the use of classes, which is why we spend an entire chapter discussing them.

USING STRUCTURES

In Chapter 2 you were introduced to the concept of the abstract data type. To implement an ADT in VB.NET, we need to use a special data type called a structure. A structure allows us to store multiple components of different data types in one logical unit. In some languages structures are known as records.

The atomic data types (Integer, Single, String) allow us to store only single data items in a variable, as does an array (well, not strictly, since an array can be of type Object). For example, when we store a number in an Integer variable, we can only store one number in the variable. With structures, we can store more than one piece of the data in the structure and the data can be of different types.