Microsoft WSH and VBScript Programming for the Absolute Beginner Part 18 docx

‘Formally declare each variable used by the script before trying to ‘use them Dim objWshShell, strAnswer, strCardImage, intGetRandomNumber ‘Create an instance of the WScript object in or

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You can expand the Ifstatement by adding one or more ElseIfkeywords, each of which can test another alternative condition For example, look at the following VBScript statements:

If X = 250 Then

WScript.Echo “Go and buy that TV!”

WScript.Echo “Buy a TV Guide while you are at it.”

WScript.Echo “And do not forget to say thank you.”

ElseIf X = 200 Then

WScript.Echo “Buy the VCR”

ElseIf X = 100 Then

WScript.Echo “Buy the Radio.”

Else

WScript.Echo “OK Maybe you had best just eat lunch.”

End If

Nesting If Statements

Another way to use Ifstatements is to embed them within one another This enables you to develop scripts that test for a condition and then further test other conditions based on the result of the previous test To see what I mean, look at the following example (I have bolded the embedded Ifstatement to make it easier to see):

X = 250

If X = 250 Then

In the Real World

A flowchart is a graphical depiction of the possible logical flow of a script or program

Pro-grammers sometimes begin script development by first creating a flowchart The flowchart serves as a visual tool for script development and provides a valuable documentation tool Flowchart development can be a big help in the creation of complex scripts Flowcharts help programmers formalize their thoughts before script development begins Sometimes an automation task requires the development of several scripts, all of which must work together Flowcharts provide a way of designing and documenting the logical flow between each script Flowcharts can also facilitate script development when multiple programmers are involved, as they can be used to break down a task into discrete parts, each of which can then be assigned

to a different person to work on

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If Weekday(date()) = 1 Then

WScript.Echo “It’s Sunday The TV store is closed on Sundays.”

Else

WScript.Echo “Go and buy that TV!” & vbCrLf & _

“Buy a TV Guide while you are at it.” & vbCrLf & _

“And do not forget to say thank you.”

End If

Else

WScript.Echo “OK Just purchase the radio for today.”

End If

In this example, the first statement performs a test to see whether the value assigned to a variable named Xis equal to 250 If it’s not equal to 250, the script skips all the statements located between the If X = 250 Thenline and the Elseline and displays the message “OK Just purchase the radio for today.” However, if the value of X is equal to 250, then the embedded Ifstatement executes This Ifstatement begins by determining whether the cur-rent day of the week is Sunday, and if it is, the script informs the user that the TV store is closed Otherwise, it tells the user to go and make the purchase

The test performed by the Ifstatement in the previous example deserves a little extra explanation As you saw, it retrieved a numeric value representing the current day of the week Here’s how to break down the logic used by this state-ment: First, it executed the built-in VBScript Date() function The value retrieved by this function was then used by the built-in VBScript Weekday() function to determinate the numeric value that represents the current day of the week These values are 1 = Sunday, 2 = Monday, 3 = Tuesday, 4 = Wednesday,

5 = Thursday, 6 = Friday, 7 = Saturday Once this value was established, the If statement simply checked to see if it was equal to 7 (Sunday)

As you can see, by taking advantage of built-in VBScripts functions you can per-form some fairly complex tasks with minimal coding It’s a good idea to always check to see whether VBScript has a built-in function before attempting to write

a piece of code to perform a generic task, such as date manipulation or checking

By embedding, or nesting one Ifstatement within another Ifstatement, you can develop complex programming logic There’s no limit on the number of If statements you can embed within one another, although going more than a few layers deep can become confusing and difficult to follow.

H I N T

T R I C K

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RockPaperScissors.vbs Revisited

Okay You’ve now learned a lot about the Ifstatement, including its syntax and various ways

in which it can be used One of the biggest challenges that I faced in coming up with the VBScript examples for the first four chapters of this book was how to create VBScript-based games without using VBScript programming statements that I had not yet covered For the most part I was successful, but there was one exception: I just could not avoid using the If statement—although I tried to use it as little as possible In most cases, this meant limiting the completeness of the games presented

One such game was the RockPaperScissors.vbsgame Now that I’ve finally provided a com-plete review of the Ifstatement, let’s revisit the game and see how we can make it better

‘Formally declare each variable used by the script before trying to

‘use them

Dim objWshShell, strAnswer, strCardImage, intGetRandomNumber

‘Create an instance of the WScript object in order to later use

‘the Popup method

Set objWshShell = WScript.CreateObject(“WScript.Shell”)

‘Display the rules of the game

objWshShell.Popup “Welcome to Rock, Paper, and Scissors game “ & _

“Here are the “ & _

“rules of the game: 1 Guess the same thing as the computer “ & _

“to tie 2 Paper covers rock and wins 3 Rock breaks “ & _

“scissors and wins 4 Scissors cut paper and win.”

‘Prompt the user to select a choice

strAnswer = InputBox(“Type Paper, Rock, or Scissors.”, _

“Let’s play a game!”)

‘Time for the computer to randomly pick a choice

Randomize

intGetRandomNumber = Round(FormatNumber(Int((3 * Rnd) + 1)))

‘Assign a value to the randomly selected number

If intGetRandomNumber = 3 then strCardImage = “rock”

If intGetRandomNumber = 2 then strCardImage = “scissors”

If intGetRandomNumber = 1 then strCardImage = “paper”

‘Display the game’s results so that the user can see if he won

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objWshShell.Popup “You picked: “ & strAnswer & Space(12) & _

“Computer picked: “ & strCardImage

Figure 5.6 shows the output of a complete game as the script currently is written.

First off, let’s update the script by adding the script template that was introduced back in Chapter 3, “VBScript Basics.”

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

‘Script Name: RockPaperScissors-2.vbs

‘Author: Jerry Ford

‘Created: 11/16/02

‘Description: This script revisits the RockPaperScissors.vbs script, first

‘introduced in Chapter 2, and updates it using advanced conditional logic

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

Next, let’s rewrite the Dimstatement by adding another variable called Results

Dim objWshShell, strAnswer, strCardImage, strResults

Resultsis used later in the scripts to store the results of the game (that is, who wins and who loses) Next let’s add the following statement to the script:

This statement creates an instance of the objWshShellobject This object’s Quit()method is used later in the script to terminate its execution in the event that the user fails to provide

a valid selection (that is, the player does not pick rock, paper, or scissors)

Now that the variables and objects to be used by the script have been defined, let’s assign a default value of Noneto the strResultsvariable, like this:

strResults = “None”

Unless the player provides a correction selection, this value will remain equal to None throughout the script’s execution, and will eventually cause the script to terminate and dis-play an error message However, if the dis-player supplies a correct response, the response will

be assigned to the strResultsvariable and then will be analyzed by the script

Figure 5.6

Playing Rock,

Paper, and

Scissors

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The original RockPaperScissors.vbs script displayed the game’s instructions in one popup dialog, and then prompted the player to specify a selection of rock, paper, or scissors in a second pop-up dialog This works, but using two pop-up dialogs is a bit clunky Let’s modify the scripts to display the game’s directions and collect the player’s input at the same time, like this:

strAnswer = InputBox(“Please type paper, rock, or scissors.” & _

vbCrLf & vbCrLf & “Rules:” & vbCrLf & vbCrLf & _

“1 Guess the same thing as the computer to tie.” & vbCrLf & _

“2 Paper covers rock and wins.” & vbCrLf & _

“3 Rock breaks scissors and wins.” & vbCrLf & _

“4 Scissors cut paper and win.” & vbCrLf, “Let’s play a game!”)

As you can see, I used the VBScript InputBox()function to display the pop-up dialog, and I formatted the instructions for better presentation using the vbCrLfconstant.

The next two sections of the script remain the same as in the original script

Randomize

As explained in Chapter 2, “Overview of the Windows Script Host,” the first pair of state-ments results in the selection of a random number with a value between 1 and 3 The next three lines assign a value of rock, paper, or scissors to each of these values The rest of the script will be comprised of all new code Instead of simply displaying the player’s and the script’s selection of rock, paper, or scissors and then leaving it up to the player to figure out who won, the script now performs the analysis To begin, add the following lines to the bot-tom of the script:

If strAnswer = “rock” Then

If intGetRandomNumber = 3 Then strResults = “Tie”

If intGetRandomNumber = 2 Then strResults = “You Win”

If intGetRandomNumber = 1 Then strResults = “You Lose”

End If

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This set of statements executes only if the player typed rock Three Ifstatements then com-pare the user’s selection to the script’s randomly selected decisions and determine the results of the game Now replicate this collection of statements two times, and then modify each set as follows to add tests for the selection of both scissors and paper:

If strAnswer = “scissors” Then

End If

If strAnswer = “paper” Then

End If

Now add the following statements to the script:

If strResults = “None” Then

objWshShell.Popup “Sorry Your answer was not recognized “ & _

“Please type rock, paper, or scissors in all lowercase letters.”

WScript.Quit

End If

These statements only execute if the player fails to provide a correct response when playing the game If this happens, the value of strResultsis never changed and will still be set equal

to None as assigned at the beginning of the script In this case, the objWshShell object’s Popup()and Quit()methods are used to display an error message and then end the game Now let’s wrap up this script by adding these last few lines of code.

objWshShell.Popup “You picked: “ & space(12) & strAnswer & vbCrLf & _

vbCrLf & “Computer picked: “ & space(2) & strCardImage & vbCrLf & _

vbCrLf & “================” & vbCrLf & vbCrLf & “Results: “ & _

strResults

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These statements are only executed if the player provided a valid response They used the objWshShellobject’s Popup()method to display the results of the game, including both the player’s and the script’s selections

The fully assembled script should now look like the following:

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

‘Script Name: RockPaperScissor-2.vbs

‘Created: 11/16/02

‘Description: This script revisits the RockPaperScissors.vbs script first

‘introduced in Chapter 2 and updates it using advanced conditional logic

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

‘Perform script initialization activities

Dim objWshShell, strAnswer, strCardImage, strResults

strResults = “None”

‘Prompt the user to select a choice

strAnswer = InputBox(“Please type paper, rock, or scissors.” & _

vbCrLf & vbCrLf & “Rules:” & vbCrLf & vbCrLf & _

“1 Guess the same thing as the computer to tie.” & vbCrLf & _

“2 Paper covers rock and wins.” & vbCrLf & _

“3 Rock breaks scissors and wins.” & vbCrLf & _

“4 Scissors cut paper and win.” & vbCrLf, “Let’s play a game!”)

‘Time for the computer to randomly pick a choice

Randomize

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‘When you select rock

If strAnswer = “rock” Then

End If

‘When you select scissors

If strAnswer = “scissors” Then

End If

‘When you select paper

If strAnswer = “paper” Then

End If

If strResults = “None” Then

WScript.Quit

End If

objWshShell.Popup “You picked: “ & space(12) & strAnswer & vbCrLf & _

vbCrLf & “Computer picked: “ & space(2) & strCardImage & vbCrLf & _

vbCrLf & “================” & vbCrLf & vbCrLf & “Results: “ & _

strResults

Save and execute the script Figure 5.7 shows the initial pop-up dialog displayed by the script.

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Figure 5.8 shows the results of a typical game.

The Select Case Statement

The If statement provides a great tool for testing two expressions Using ElseIf you can modify the Ifstatement to perform additional tests VBScripts supplies another statement, called Select Case, which also lets you perform comparative operations Functionally, it’s not really very different from the Ifstatement However, the Select Case statement is better equipped to perform large numbers of tests against a single expression

Here is the syntax of the Select Casestatement:

Select Case expression

Case value

statements

Case value

statements

Case Else

statements

End Select

Figure 5.7

The new version

of RockPaper

Scissors.vbs

displays a

friendlier initial

dialog

Figure 5.8

The results of

a typical game

of the new

version of

RockPaper

Scissors.vbs

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The Select Casestatement begins with Select Case, and then specifies the expression to be compared against one or more values specified in Casestatements that follow the Select Casestatement and precede the End Select statement Optionally, a Case Elsestatement can also be added to provide an alternative course of action should none of the Casestatement’s values match up against the expression specified by the Select Casestatement

Look at the following example:

Select Case strAnswer

Case “rock”

Case “scissors”

Case “paper”

Case Else

WScript.Quit

End Select

Here I have rewritten most of the logic implemented in the RockPaperScissors.vbsscript As the following complete script shows, not only did I reduce the number of lines of code required by the script to work, but I also improved the script’s readability:

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

‘Script Name: RockPaperScissors-3.vbs

‘Created: 11/16/02

‘Description: This script revisits the RockPaperScissors-2.vbs script,

‘replacing some of the If statement’s logic with a Case Select statement

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

‘Perform script initialization activities

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