Microsoft WSH and VBScript Programming for the Absolute Beginner Part 13 pps

One of the key concepts that you need to understand when working with VBScript, or any programming language, is how to store, retrieve, and modify data.. Specifically, you will learn how

100 Microsoft WSH and VBScript Programming for the Absolute Beginner, Second Edition

CH A L L E N G E S

1 Change the Math Game to use a different equation and modify the logic required

to adapt the statements that work with the WordPad and Calculator applications

2 Try using the SendKeys() method to work with other Windows applications, such

as Notepad

3 Spend some time reviewing VBScript built-in math functions and see if you can create a new calculator similar to the Square Root calculator.

4 Modify the VBScript template presented earlier in this chapter and adapt it to suit your personal preferences, and then use it as you begin developing new VBScripts.

Constants, Variables, and

Arrays

4

This is the second of five chapters in this book that teaches the

funda-mentals of VBScript One of the key concepts that you need to understand when working with VBScript, or any programming language, is how to store, retrieve, and modify data This chapter will teach you a number of different ways to perform these tasks By the time you have completed this chapter, you will know how to write scripts that can collect and manipulate data Specifically, you will learn how to

• Process data passed to the script at execution time

• Store data that does not change

• Work with data that can change during script execution

• Process collections of related data as a unit

Project Preview:

The Story of Captain Adventure

In this chapter, you will learn how to create a game that builds a comical adven-ture story based on user input The game begins by collecting answers to a series

of questions without telling the user how the answers will be used After all the information that the script needs is collected, the story is displayed, as shown in Figures 4.1 through 4.7

102 Microsoft WSH and VBScript Programming for the Absolute Beginner, Second Edition

Figure 4.1

The story’s initial

splash screen.

Figure 4.2

The user is the

star of the story

Figure 4.3

The story begins

anywhere the

user specifies.

Figure 4.4

The user must

specify the object

that provides our

hero with his

superpowers.

Figure 4.5

The user specifies

the story’s

co-star.

Through the development of this story-building game, you will learn a number of important programming techniques, including how to collect, store, and reference data In addition, you will learn how to control the presentation of script output

Understanding How Scripts View Data

VBScript, like other programming languages, needs a way of storing data so that it can be accessed throughout the execution of a script Up to this point in the book, you have seen a number of examples of how VBScript temporarily stores and references data Now I’ll explain how this works

VBScript supplies a number of different statements

that allow you to define several different types of data

These VBScript statements are outlined in Table 4.1

Figure 4.6

Finally, the user

specifies a

magic word.

Figure 4.7

After the script

has all the

information it

needs, the

story is told.

Definition

Data is information that a computer

program collects, modifies, stores, and retrieves during execution.

The Conststatement is used to define data that never changes throughout the execution of

a script For example, in this book you will sometimes see constants used to define strings that are used to define a standard greeting message in pop-up dialog boxes The Dim

state-ment is used to define a variable A variable stores an individual piece of data such as a name,

number, or date The ReDim statement is used to create an array Arrays are used to store

groups of related information For example, instead of defining 20 different variables to store information about 20 different people, a single array could be defined and then infor-mation about each person can be stored in it Each of these statements will be examined in greater detail throughout the rest of this chapter

Working with Data That Never Changes

Data should be defined within a script according to the manner in which it will be used If the script only needs to reference a piece of data that has a value that is known during script development, then the data can be defined as a constant An example of a constant is the mathematical value of pi Other examples of constants include specific dates of history, the name of places, and so on

There are two sources of constants within scripts First, you can define your own constants within your scripts Another option is to reference a built-in collection of readily available constants provided by VBScript

Assigning Data to Constants

If you’re going to write a script and know for a fact that you need to reference one or more values that will not change during the execution of the script, then you can define each piece of data as a constant One of the nice features of constants is that, once defined, their

Microsoft WSH and VBScript Programming for the Absolute Beginner, Second Edition

Dim Defines a VBScript variable or array

TA B L E 4 1 V B SC R I P T ST A T E M E N T S TH A T DE T E R M I N E

HO W DA T A IS DE F I N E D

value cannot be changed This prevents their values from being accidentally modified dur-ing the execution of the script

If your script attempts to modify the value assigned to a constant after it has been initially assigned, you will see an “Illegal assignment: ‘XXXXXXXX’ ” error message when the script executes XXXXXXXX will reference the name of the constant Open your script and do a search on this word and look for the state-ments that have attempted to modify its value to find the source of the error

To define a constant within a VBScript, you must use the Const statement This statement has the following syntax:

[Public | Private] Const ConstName = expression

Publicand Privateare optional keywords and are used

to determine the availability of constants throughout

a script Defining a constant as Publicmakes it

avail-able to all procedures within the scripts Defining a

constant as Privatemakes it available only within the

procedure that defines them ConstNameis the name of

the constant being defined, and expression is the

value that identifies the data being defined To make

sense of all this, let’s look at an example

‘*************************************************************************

‘Script Name: LittlePigs.vbs

‘Author: Jerry Ford

‘Created: 02/28/02

‘Description: This script demonstrates how to use a constant to create a

‘standardized title bar message for pop-up dialogs displayed by the script

‘*************************************************************************

‘Specify the message to appear in each pop-up dialog title bar

Const cTitleBarMsg = “The Three Little Pigs”

‘Display the story

MsgBox “Once upon a time ”, vbOkOnly, cTitleBarMsg

MsgBox “There were 3 little pigs”, vbOkOnly, cTitleBarMsg

MsgBox “Who liked to build things.”, vbOkOnly, cTitleBarMsg

H I N T

Definition

A procedure is a collection of script

statements that are processed as a unit In Chapter 7, “Using Procedures

to Organize Scripts,” you will learn how to use procedures to improve the overall organization of your scripts and to create reusable units

of code.

In this example, I wrote a small VBScript that tells a very brief story about three little pigs The script begins by defining a constant named cTitleBar I then used three MsgBox() state-ments to display the text that makes up the story The first argument in each MsgBox()statement

is a text message, which is then followed by a VBScript MsgBox()constant vbOkOnly This con-stant tells VBScript to only display the OK button on the pop-up dialog (a complete listing of

MsgBox()constants is available in Chapter 3, “VBScript Basics.” The last part of each MsgBox()

statement is the cTitleBarMsg constant VBScript automatically substitutes the value assigned to the cTitleBarMsgconstant whenever the script executes Figure 4.8 shows how the first pop-up dialog appears when the script is executed

I strongly recommend that you apply a naming convention for your constants that will uniquely identify them within your scripts A good naming convention will make your constants easy to locate and identify and will improve the over-all readability of your scripts For example, in this book I will use the following constant naming convention:

• Constant names begin with the lowercase letter c

• Constant names describe their contents using English words or easily identifiable parts of words

Other examples of tasks related to working with constants include assigning values such as numbers, strings, and dates For example, the following statement assigns a value of 1000to

a constant called cUpperLimit:

Const cUpperLimit = 1000

To define a text string, you must place the value being assigned within a pair of quotes, like this:

Const cMyName = “Jerry Lee Ford, Jr.”

H I N T

Microsoft WSH and VBScript Programming for the Absolute Beginner, Second Edition

Figure 4.8

By referencing

the value

assigned to a

constant, you can

create a standard

title bar message

for every pop-up

dialog displayed

by your script

In a similar fashion, you must use a pair of pound signs to store a date value within a con-stant, like this:

Const cMyBirthday = #11-20-64#

VBScript Run-Time Constants

VBScript supplies you with an abundance of built-in constants In Chapter 3 you learned about the constants associated with the MsgBox() function For example, the following VBScript statement executes the MsgBox()function using the vbOkOnlyconstant:

MsgBox “Welcome to my VBScript game!”, vbOkOnly

This statement displays a pop-up dialog that contains a single OK button In addition to these constants, VBScript supplies constants that help when you’re working with dates and times VBScript also supplies a number of constants that can help you manipulate the dis-play of text output and test the type of data stored within a variable

Using Date and Time Constants

Table 4.2 lists VBScript Date and Time constants

vbFirstFourDays 2 First full week with a minimum of 4 days in the new year

vbUseSystemDayOfWeek 0 Day of week as specified by the operating system

TA B L E 4 2 V B SC R I P T DA T E A N D TI M E CO N S T A N T S

The following script demonstrates how the vbFridayconstant, listed in Table 4.2, can be used

to determine whether the end of the workweek is here:

‘*************************************************************************

‘Script Name: HappyHour.vbs

‘Author: Jerry Ford

‘Created: 10/26/02

‘Description: This script tells the user if it’s Friday

‘*************************************************************************

‘Perform script initialization activities

Dim TodaysDate

‘ Weekday is a VBScript function that gets the day of the week

TodaysDate = Weekday(Date)

If TodaysDate = vbFriday then MsgBox “Hurray, it is Friday Time “ & _

“to get ready for happy hour!”

You may have noticed the use of the &character in the previous example The &

character is a VBScript string concatenation operator It allows you to combine two pieces of text into a single piece of text

The first two lines of the script define a variable (we’ll discuss variables in detail in the next section) The third line assigns a numeric value to the variable In this case, the script used the VBScript Weekday()function to execute the VBScript Date()function The Date() func-tion retrieves the current date from the computer The Weekday()function then provides a numeric value to represent the weekday for the date Table 4.2 provides a list of the possible range of values in its Value column If the current day of the week is Friday, then the value returned by the Weekday()function will be 6 Because the vbFridayconstant has a value of 6, all that has to be done to determine if it is Friday is to compare the value returned by the

Weekday()function to the vbFriday If the two values are equal, a pop-up dialog displays the message “Hurray, it is Friday Time to get ready for happy hour!”

Using String Constants

Another group of constants that you may find useful are the VBScript string constants listed

in Table 4.3

T R I C K

Microsoft WSH and VBScript Programming for the Absolute Beginner, Second Edition

Using the constants shown in Table 4.3, you can control the manner in which output text is displayed For example, take a look at the following script:

‘*************************************************************************

‘Script Name: MsgFormatter.vbs

‘Author: Jerry Ford

‘Created: 02/28/02

‘Description: This script demonstrates how to use VBScript string constants

‘to control how text messages are displayed.

‘*************************************************************************

‘Specify the message to appear in each pop-up dialog title bar

Const cTitleBarMsg = “The three little pigs”

‘Specify variables used by the script

Dim StoryMsg

‘Specify the text of the message to be displayed

vbCrLf Chr(13) and Chr(10) Executes a carriage return and a line feed

vbNewLine Chr(13) and Chr(10) Adds a newline character

vbNullString String with no value Creates an empty string

TA B L E 4 3 V B SC R I P T ST R I N G CO N S T A N T S