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

100 Microsoft WSH and VBScript Programming for the Absolute Beginner, Second Edition C HALLENGES 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 CHAPTER T his 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. CHAPTER 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. 103 Chapter 4 • Constants, Variables, and Arrays 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. 104 The Const statement 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 Statement Description Const Defines a VBScript constant Dim Defines a VBScript variable or array ReDim Defines a dynamic VBScript array TABLE 4.1 VBSCRIPT STATEMENTS T HAT D ETERMINE H OW D ATA I S D EFINED 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 Public and Private are optional keywords and are used to determine the availability of constants throughout a script. Defining a constant as Public makes it avail- able to all procedures within the scripts. Defining a constant as Private makes it available only within the procedure that defines them. ConstName is 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 HINT 105 Chapter 4 • Constants, Variables, and Arrays 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. 106 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 cTitleBarMsg constant 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 1000 to 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.” HINT 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 vbOkOnly constant: 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. 107 Chapter 4 • Constants, Variables, and Arrays Constant Value Description vbSunday 1 Sunday vbMonday 2 Monday vbTuesday 3 Tuesday vbWednesday 4 Wednesday vbThursday 5 Thursday vbFriday 6 Friday vbSaturday 7 Saturday vbFirstFourDays 2 First full week with a minimum of 4 days in the new year vbFirstFullWeek 3 First full week of the year vbFirstJan1 1 Week that includes January 1 vbUseSystemDayOfWeek 0 Day of week as specified by the operating system TABLE 4.2 VBSCRIPT D ATE AND T IME C ONSTANTS 108 The following script demonstrates how the vbFriday constant, 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 vbFriday constant 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. TRICK Microsoft WSH and VBScript Programming for the Absolute Beginner, Second Edition 109 Chapter 4 • Constants, Variables, and Arrays 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 Constant Value Description vbCr Chr(13) Executes a carriage return vbCrLf Chr(13) and Chr(10) Executes a carriage return and a line feed vbFormFeed Chr(12) Executes a form feed vbLf Chr(10) Executes a line feed vbNewLine Chr(13) and Chr(10) Adds a newline character vbNullChar Chr(0) Creates a 0 or null character vbNullString String with no value Creates an empty string vbTab Chr(9) Executes a horizontal tab vbVerticalTab Chr(11) Executes a vertical tab TABLE 4.3 VBSCRIPT STRING C ONSTANTS . 4.7. CHAPTER 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. 100 Microsoft WSH and VBScript Programming for the Absolute Beginner, Second Edition C HALLENGES 1. Change the Math Game to use a different equation and modify the logic required to adapt the. “Jerry Lee Ford, Jr.” HINT 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