Visual Basic.NET How to Program (PDF)

62 Introduction to Visual Basic Programming Chapter 3
James Fenimore Cooper
Outline
3.1 Introduction
3.2 Simple Program: Printing a Line of Text
3.3 Another Simple Program: Adding Integers
3.4 Memory Concepts
3.5 Arithmetic
3.6 Decision Making: Equality and Relational Operators
3.7 Using a Dialog to Display a Message
3.8 Internet and World Wide Web Resources
Summary Terminology Self-Review Exercises Answers to Self-Review Exercises Exercises
3.1 Introduction
Visual Basic .NET enables a disciplined approach to computer-program design. In this
chapter, we introduce Visual Basic programming and present examples that illustrate several
important features of the language. To help readers better understand the examples in
this and other chapters, program code is analyzed one line at a time. In this chapter, we introduce
console applications—applications that contain only text output. There are several
types of Visual Basic projects; the console application is one of the simplest types. Text
output in a console application is displayed in a command window (also called a console
window). On Microsoft Windows 95/98, the command window is called the MS-DOS
prompt; on Microsoft Windows NT/2000/XP, the command window is called the command
prompt. With a sophisticated language like Visual Basic, programmers can create programs
that input and output information in a variety of ways, which we discuss throughout the
book. For instance, in Chapter 2, we created a simple graphical user interface (GUI) for a
Windows application, using visual programming techniques. Windows applications are
discussed in greater detail in Chapters 4 and 5, Control Structures: Part 1 and Control Structures:
Part 2, respectively. These chapters provide a more detailed introduction to program
development in Visual Basic.
3.2 Simple Program: Printing a Line of Text
Visual Basic .NET uses some notations that might appear strange to nonprogrammers. To
explain these notations, we begin by considering a simple program (Fig. 3.1) that displays
a line of text. When this program is run, the output appears in a command window.
This program illustrates several important Visual Basic features. For the reader’s convenience,
all program listings in this text include line numbers—these line numbers are not
part of Visual Basic programs. In addition, each program is followed by one or more windows
showing the program’s output.
Line 1 begins with a single-quote character (') which indicates that the remainder of
the line is a comment. Programmers insert comments in a program, or code listing, to
improve the readability of their code. Comments can be placed either on their own line (we
call these “full-line comments”) or at the end of a line of Visual Basic code (we call these