Programming Visual Basic .NET, Second Edition

Iteration (Looping) Statements

There are many situations in which you will want to do the same thing again and again, perhaps slightly changing a value each time you repeat the action. This is called iteration or looping. Typically, you’ll iterate (or loop) over a set of items, taking the same action on each. This is the programming equivalent to an assembly line. On an assembly line, you might take a hundred car bodies and put a windshield on each one as it comes by. In an iterative program, you might work your way through a collection of text boxes on a form, retrieving the value from each in turn and using those values to update a database.

VB.NET provides an extensive suite of iteration statements, including Do, For, and For Each. You can also create a loop by using a statement called Goto. This chapter considers the use of Goto, Do, and For. However, you’ll have to wait until Chapter 3 to learn more about For Each.

Creating Loops with Goto

Goto is the most primitive kind of unconditional branching statement, and it is not much used in modern programming. Its most common usage was to create looping statements, and in fact, the Goto statement is the seed from which all other looping statements have been germinated. Unfortunately, it is a semolina seed, producer of spaghetti code and endless confusion.

Programs that use Goto statements jump around a great deal. Goto can cause your method to loop back and forth in ways that are difficult to follow.

If you were to try to draw ...