Microsoft Visual Basic 2010 Step by Step eBook

288 Part II Programming Fundamentals

Using ReDim for Three-Dimensional Arrays

A more complex example involving a three-dimensional array uses a similar syntax. Imagine

that you want to use a three-dimensional, single-precision, floating-point array named

myCube in your program. You can declare the myCube array by using the following syntax:

Dim myCube(,,) As Single

You can then redimension the array and add data to it by using the following code:

ReDim myCube(25, 25, 25)

myCube(10, 1, 1) = 150.46

after which you can expand the size of the third dimension in the array (while preserving the

array’s contents) by using this syntax:

ReDim Preserve myCube(25, 25, 50)

In this example, however, only the third dimension can be expanded—the first and

second dimensions cannot be changed if you redimension the array by using the Preserve

keyword. Attempting to change the size of the first or second dimension in this example

produces a run-time error when the ReDim Preserve statement is executed.

Experiment a little with ReDim Preserve, and see how you can use it to make your own arrays

flexible and robust.

One Step Further: Processing Large Arrays

by Using Methods in the Array Class

In previous sections, you learned about using arrays to store information during program

execution. In this section, you’ll learn about using methods in the Array class of the .NET

Framework, which you can use to quickly sort, search, and reverse the elements in an array,

as well as perform other functions. The sample program I’ve created demonstrates how

these features work especially well with very large arrays. You’ll also learn how to use the

ProgressBar control.

The Array Class

When you create arrays in Visual Basic, you are using a base class that is defined by Visual

Basic for implementing arrays within user-created programs. This Array class also provides

a collection of methods that you can use to manipulate arrays while they are active in

programs. The most useful methods include Array.Sort, Array.Find, Array.Reverse, Array

.Copy, and Array.Clear. You can locate other interesting methods by experimenting with

the Array class in the Code Editor (by using Microsoft IntelliSense) and by checking the