Microsoft Visual Basic 2010 Step by Step eBook

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Chapter 6

Using Decision Structures

After completing this chapter, you will be able to:

n Write conditional expressions.

n Use an If... Then statement to branch to a set of program statements based on

a varying condition.

n Use the MaskedTextBox control to receive user input in a specific format.

n Short-circuit an If... Then statement.

n Use a Select Case statement to select one choice from many options in program code.

n Use the Name property to rename objects within a program.

n Manage mouse events and write a MouseHover event handler.

In the past few chapters, you used several features of Microsoft Visual Basic 2010 to process

user input. You used menus, toolbars, dialog boxes, and other Toolbox controls to display

choices for the user, and you processed input by using property settings, variables, operators,

formulas, and the Microsoft .NET Framework.

In this chapter, you’ll learn how to branch conditionally to a specific area in your program

based on input you receive from the user. You’ll also learn how to evaluate one or more

properties or variables by using conditional expressions, and then execute one or more

program statements based on the results. In short, you’ll increase your programming

vocabulary by creating code blocks called decision structures that control how your program

executes, or flows, internally.

Event-Driven Programming

The programs you’ve written so far in this book have displayed Toolbox controls, menus,

toolbars, and dialog boxes on the screen, and with these programs, users could manipulate

the screen elements in whatever order they saw fit. The programs put the user in charge,

waited patiently for a response, and then processed the input predictably. In programming

circles, this methodology is known as event-driven programming. You build a program by

creating a group of “intelligent” objects that know how to respond to input, and then the

program processes the input by using event procedures associated with the objects.

Where does this input come from? Fundamentally, of course, most input comes from the user

of your program, who is opening menus, clicking the mouse, typing in text boxes, and so on.

However, program input can also come from the computer system itself. For example, your

program might be notified when a piece of e-mail arrives or when a specified period of time

Table of Contents

Using Decision Structures.................................. 159

Event-Driven Programming.......................................... 159

Using Conditional Expressions........................................ 161

If... Then Decision Structures................................. 161

Testing Several Conditions in an If... Then

Decision Structure............................................. 162

Using Logical Operators in Conditional Expressions................ 167

Short-Circuiting by Using AndAlso and OrElse................... 169

Select Case Decision Structures...................................... 171

Using Comparison Operators with a Select

Case Structure................................................. 173

One Step Further: Detecting Mouse Events............................ 177

Chapter 6 Quick Reference........................................... 179