The Internet Encyclopedia (Volume 3)

P1: JDT

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VBSCRIPTLANGUAGEFUNDAMENTALS 625

Figure 1: What the user sees when running either of the

scripts given in Listings 2 and 3.

IsNumeric() function which returns a Boolean value in-

dicating if data are or can be transformed into a numeric

variant subtype. Note that what the user sees is identical

regardless of which of these two scripts is executed.

Figure 1 shows what the user sees when running either

of the scripts given in Listings 2 and 3.

Listing 2:VBScript illustrating If...Then...Else program

flow control.

Option Explicit

Dim strMyVar, intMyVar

Do

strMyVar = InputBox_

("Enter a number between 1 and 3")

Loop Until IsNumeric (strMyVar)

intMyVar = CInt(strMyVar)

If intMyVar = 1 then

MsgBox ("You Entered the Lowest Option.")

ElseIf intMyVar = 2 then

MsgBox ("You Entered the Middle Option.")

ElseIf intMyVar = 3 then

MsgBox ("You Entered the Highest Option.")

Else

MsgBox_

("You Entered a Number Too Small or Too

Big!")

End If

Listing 3:Script illustrating Select Case program flow control.

Option Explicit

Dim strMyVar, intMyVar

Do

strMyVar = InputBox_

("Enter a number between 1 and 3")

Loop Until IsNumeric (strMyVar)

intMyVar = CInt(strMyVar)

Select Case intMyVar

Case 1

MsgBox ("You Entered the Lowest Option.")

Case 2

MsgBox ("You Entered the Middle Option.")

Case 3

MsgBox ("You Entered the Highest Option.")

Case Else

MsgBox_

("You Entered a Number Too Small or Too

Big!")

End Select

User-Defined Procedures

In addition to intrinsic functions, VBScript allows pro-

grammers to define their own functions and subroutine

procedures. User-defined functions, code blocks that be-

gin with the key word “Function” and end with an “End

Function” statement, return a single value. Since VB-

Script only allows variant data type, all functions return

a variant; therefore a data type is not included in a func-

tion declaration (as it typically is when declaring func-

tions in Visual Basic and VBA). User-defined subroutines,

code blocks that begin with the key word “Sub” and end

with an “End Sub” statement, do not return a specific

value, but rather perform tasks (including input, output,

and user dialog tasks) and may affect values of script-

level (i.e., global) scope variables. Variables and named

constants declared in functions and subroutines have a

procedure-level (i.e., local) scope and are not directly visi-

ble to the calling routine. (However care must be taken not

to try to use a script-level variable with the same name as

a variable local to a particular subroutine or function.)

Local scope variable values set or changed during one

call to a subroutine or function do not carry over to sub-

sequent calls. Subroutines and functions may be called

recursively (i.e., may call themselves), though great care

must be exercised when doing so. By default, argument

variables needed by a user-defined subroutine or function

are passed by reference. This means a pointer to each ar-

gument variable in memory is passed. Any modifications

to an argument variable that happen in a subroutine or

function persist when control is passed back to the calling

procedure. A programmer may use the ByVal key word in

the subroutine or function declaration—e.g., “Sub MySub

(ByVal myVar)”—in order to override this default behav-

ior. Arguments passed by value remain unchanged when

control passes back to the calling procedure, regardless of

what is done in the subprocedure.

VBScript Coding Conventions

Over time, the community of programmers using any

given language tends to develop conventions in areas such

as naming patterns for variables and constants, the way

program commentary is incorporated, and the way code is

formatted and indented. While there is no compulsion to