Back to Basics: VBScript for ASP - Part 2

Introduction

Last month marked the start of our journey into learning basic server-side VBScript for use in ASP pages. We learned about variables and types, conditional testing and some looping. This month we will take a look at some slightly higher-level techniques that can be very useful for making your ASP pages more functional and well-polished. We begin with a discussion of Arrays.

Array Basics

Arrays are a very useful "tool" at your disposal as a developer. Very simply put, arrays give you the power to store multiple values in just one variable. An even better way to think of an array is to return to your algebra days in middle school or high school. Remember matrices? Basically they are a table of numbers or variables upon which you could perform various operations. Arrays are just that, matrices in your computer.

Arrays in VBScript are easy to implement and to use, you just need to be clear on the syntax and how they work conceptually. Let's begin by taking a look at setting one up and using it.

Dim myArray(10)
Dim myString

myArray(0) = "Power of"
myArray(1) = "Cheese"

myString = "The " + myArray(0) + " " + myArray(1)

The code snippet above does a couple of simple tasks. First, it initializes the array, called myArray using a Dim statement. Notice how myArray is followed by (). Those two parentheses with a number inside determine that the variable is of sub-type array and how many values it holds. This particular array holds ten values (of which we use only 2).

Okay here comes the hard part. myArray holds ten values, or elements, but in VBScript arrays are zero-based - that means they start counting from zero instead of one. Therefore, the first element of every VBScript array is zero! Having an array with ten elements means myArray(9) is the last element not myArray(10). Do not get that confused or you will be pulling your hair out for hours on end trying to figure out why your code is generating so many hiccups.

As you can see, to set an element of an array equal to something like a string, number or even another array, it is as simple as using the equals operator. Reference the appropriate element within the parentheses on the left, provide some value on the right and you are good to go. Above, I have set element zero to "Power of" and element one to "Cheese." Then, I combine all these values in myString to form the phrase: "The Power of Cheese."

Working with Arrays

There are also other ways to use an array, and even other ways of declaring one. Let's take the following example and work through it to its conclusion using arrays. Assume that you need to collect a number of survey responses but do not know beforehand how many will come back in. We will also assume that each survey only asks one question and the answer is either "True" or "False." Without worrying about processing the results after we have stored them, how can we do this using VBScript and arrays?

First, we need to determine what variables we will need and then declare them. I can think of two to start.

<%
	Dim surveyResults()
	'Notice how I left the parentheses blank
	'since we do not know how many there are yet,
	Dim numResults
%>

So far we have declared two variables. One is an array with no length, called surveyResults. The other is a variable of type variant called numResults. So far so good. To continue, we must add another assumption to our example, that is, that the administrator of these surveys is prompted for the number of results in the survey. I do not want to get into that here, so when we set numResults to some value, pretend it was first obtained from the user.

<%
	Dim surveyResults()
	Dim numResults

	'pretend the user is prompted for
	'the following line - perhaps via
	'an HTML form.
	numResults = 12

	ReDim Preserve surveyResults(numResults)
%>

Okay, so there are twelve survey results, the next step would be to change the length of the array (or the number of elements in it) to twelve. This step is done using the ReDim statement above. ReDim works just like Dim, except it handles dynamic arrays, or arrays that change their length during the life of the program. ReDim combined with Preserve ensures that all the information within our array is saved during resizing and is available to us throughout the program.

The next step involves looping through the elements of the array, and I will take that opportunity to introduce a new loop to you, the While loop!

The While Loop - Page 2