Many programmers take the concept of a variable for granted. In this chapter, we take a close look at variables and their properties, discussing such things as the scope and lifetime of a variable.
A variable can be defined as an entity that has the following six properties:
A variable’s name is used to identify the variable in code. In VB.NET, a variable name can start with a Unicode alphabetic character or an underscore, and can be followed by additional underscore characters or various Unicode characters, such as alphabetic, numeric, formatting, or combined characters.
Every variable has an associated memory address, which is the location in memory at which the variable’s value is stored. Note that in many circumstances, the address of a variable will change during its lifetime, so it would be dangerous to make any assumptions about this address.
The type of a variable, also called its data type, determines the possible values that the variable can assume. We discuss data types in detail later in the chapter.
The value of a variable is the contents of the memory location at the address of the variable. This is also sometimes referred to as the r-value of the variable, since it is what really appears on the right side of an assignment statement. For instance, in the code:
Dim i As Integer Dim j As Integer i = 5 j = i
the final statement can be read as “assign the value of i to memory at the address of j.” For ...