Visual Basic.NET 2008 > Programming Fundamentals

Control Flow Statements in Visual Basic 2008

What makes programming languages so flexible and capable of handling every situation and programming challenge with a relatively small set of commands is their capability to examine external or internal conditions and act accordingly. Programs aren't monolithic sets of commands that carry out the same calculations every time they are executed; this is what calculators (and extremely simple programs) do. Instead, they adjust their behavior depending on the data supplied; on external conditions, such as a mouse click or the existence of a peripheral; even on abnormal conditions generated by the program itself.

In effect, the statements discussed in the first half of this chapter are what programming is all about. Without the capability to control the flow of the program, computers would just be bulky calculators. You have seen how to use the If statement to alter the flow of execution in previous chapters, and I assume you're somewhat familiar with these kinds of statements. In this section, you'll find a formal discussion of flow-control statements. These statements are grouped into two major categories: decision statements and looping statements.

Decision Statements

Applications need a mechanism to test conditions and take a different course of action depending on the outcome of the test. Visual Basic provides three such decision, or conditional, statements:

• If. . .Then
• If. . .Then. . .Else
• Select Case

Loop Statements

Loop statements allow you to execute one or more lines of code repetitively. Many tasks consist of operations that must be repeated over and over again, and loop statements are an important part of any programming language. Visual Basic supports the following loop statements:

• For. . .Next
• Do. . .Loop
• While. . .End While

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