Visual Basic.NET How to Program (PDF)

82 Introduction to Visual Basic Programming Chapter 3
1000 = 1000
1000 = 1000
Notice the indentation in the If/Then statements throughout the program. Such
indentation enhances program readability.
Good Programming Practice 3.14
Indent the statement in the body of an If/Then structure to emphasize the body of the structure
and to enhance program readability. 3.14
Common Programming Error 3.3
Omission of the Then keyword in an If/Then structure is a syntax error. 3.3
The table in Fig. 3.20 shows the precedence of the operators introduced in this chapter.
The operators are displayed from top to bottom in decreasing order of precedence. All operators
in Visual Basic .NET associate from left to right.
Testing and Debugging Tip 3.3
When uncertain about the order of evaluation in a complex expression, use parentheses to
force the order, as you would do in an algebraic expression. Doing so can help avoid subtle
bugs. 3.3
3.7 Using a Dialog to Display a Message
Although the programs discussed thus far display output in the command window, most Visual
Basic programs use dialogs to display output. Dialogs are windows that typically display
messages to the user. Visual Basic provides class MessageBox for creating dialogs.
The program in Fig. 3.21 uses a dialog to display the square root of 2.
In this example, we present a program that contains a simple GUI (i.e., the dialog). The
.NET Framework Class Library (FCL) contains a rich collection of classes that can be used
to construct GUIs. FCL classes are grouped by functionality into namespaces. Line 4 is an
Imports statement that indicates we are using the features provided by the
System.Windows.Forms namespace. For example, System.Windows.Forms
contains windows-related classes (i.e., forms and dialogs). We discuss this namespace in
detail after we discuss the code in this example.
Operators Type
() parentheses
^ exponentiation
* / multiplicative
\ Integer division
Mod modulus
Fig. Fig. 3.20 3.20 Precedence and associativity of operators introduced in this chapter
(part 1 of 2).