Visual Basic 2005 in a Nutshell, Third Edition

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Chapter 4: Variables and Data Types

This is the Title of the Book, eMatter Edition

Copyright © 2006 O’Reilly & Associates, Inc. All rights reserved.

Address

Every variable has an associated memory address, the location where the vari-

able’s value is stored. Variables are not guaranteed to maintain a permanent

memory address in .NET, so the address of a variable should not be recorded

or used.

Data Type

The data type of a variable determines the possible values that the variable

can assume.

Value

The value of a variable is the data content it contains at its memory address.

This is also sometimes referred to as the r-value of the variable, since it is

what appears on the right side of a variable assignment statement. For

instance, in the code:

Dim targetValue As Integer = 5

the statement can be read as “store the value of 5 in memory at the address of

targetValue.” Because it appears on the left side of an assignment operator,

the variable (or its memory location) is sometimes called an l-value.

Scope

The scope of a variable determines where in a program that variable is visible

to the code. Variable scope is discussed in more detail later in this chapter.

Lifetime

A variable’s lifetime determines when and for how long a particular variable

exists. It may or may not be visible (that is, be in scope) for that entire period.

Variable lifetime is described in more detail later in this chapter.

Variable ...