3.52 Chapter 03 VBScript

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VBS

VBSCRIPTCRIPT – – TTHEHEBBASICSASICS... ... ... ... ... ... ... 22 W

WHAT IS A VARIABLEHAT IS A VARIABLE?...?... 33 V

VARIABLESARIABLES N NAMINGAMINGR R ESTRICTIONSESTRICTIONS... 33 H

HOWOWDDOOII CCREATE AREATE AVVARIABLEARIABLE??... 33 D

DECLARATIONECLARATIONSSTATEMENTS ANDTATEMENTS ANDHHIGHILIGTSIGHILIGTS... 33 Dim

Dim StatementStatement ... 33 Overriding

Overriding Standard Standard Variable Variable Naming Naming Conventions...Conventions... 44 Declaring

Declaring Variables Variables Explicit aExplicit and nd ImplicitImplicit ... 44 Option

Option Explicit Explicit Statement.Statement... 55 W

WORKING WITHORKING WITHAARRAYSRRAYS... ... ... ... ... ... 55 S

SCALAR CALAR VVARIABLES ANDARIABLES ANDAARRAYRRAYVVARIABLESARIABLES... 66 C

CREATINGREATINGAARRAYSRRAYS... 66 Fixed

Fixed Length Length ArraysArrays ... 66 Dynamic

Dynamic Arrays...Arrays... 66 Resizing

Resizing a a dynamic dynamic array array without without Preserve...Preserve... 77 Resizing

Resizing a a dynamic dynamic array array with with Preserve...Preserve... 77 Array

Array Iterations...Iterations... 88 VBS

VBSCRIPTCRIPTCCONSTANTSONSTANTS... ... ... ... ... ... ... 88 W

WORKING WITH CONSTANTSORKING WITH CONSTANTS... 88 D

DECLARING CONSTANTSECLARING CONSTANTS... 99 VBS

VBSCRIPT PRECRIPT PRE--DEFINED CONSTANTSDEFINED CONSTANTS... 1010 T

THEHESSCOPE ANDCOPE ANDLLIFETIME OF AIFETIME OF AVVARIABLEARIABLE... ... ... ... ... 1111 P

PRIVATERIVATESSTATEMENTTATEMENT... 1111 P

PUBLICUBLICSSTATEMENTTATEMENT... 1212 VBS

VBSCRIPTCRIPTOOPERATORSPERATORS... ... ... ... ... ... .. 1414 W

WORKING WITHORKING WITHOOPERATORSPERATORS... 1414 A

ARITHMETICRITHMETICOOPERATORSPERATORS... 1515 Addition Addition (+)(+) ...1515 Subtraction Subtraction (-)(-)... 1515 Multiplication Multiplication (*)...(*)... 1515 Division (/)

Division (/) and and Integer Integer Division (\)Division (\) ...1616 Exponent

Exponentiation iation (^) (^) ... 1616 Modulus

Modulus Arithmetic Arithmetic (Mod)...(Mod)... 1616 Unary

Unary Negation Negation (-)...(-)... 1616 String

String Concatenation Concatenation (&)(+)...(&)(+)... 1616 C

COMPARISONOMPARISONOOPERATORSPERATORS... 1616 Equality

Equality (=)...(=)... 1717 Inequality

Inequality (<>)(<>)... 1717 Less T

Less Than (<) han (<) and Greater and Greater Than (Than (>)>) ...1717 Less than or

Less than or equal (<=), greater equal (<=), greater than or equal than or equal to (>=)to (>=) ...1717 Object

Object Equivalence Equivalence (Is) (Is) ...1717 L

LOGICALOGICALOOPERATORSPERATORS... 1717 Logical

Logical Negation Negation (Not)...(Not)... 1818 Logical

Logical Conjunction Conjunction (And)...(And)... 1818 Logical

Logical Disjunction Disjunction (Or)...(Or)... 1919 Logical

Logical Exclusion Exclusion (Xor)(Xor) ...1919 Logical

Logical Equivalence Equivalence (Eqv)(Eqv) ... 2020 Logical

Logical Implication Implication (Imp)...(Imp)... 2020 F

FLOWLOWCCONTROLONTROL... ... ... ... ... ... ... 2121 C

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W

WHYHYCCONTROL THEONTROL THEFFLOW OFLOW OFCCODEODE? ? ... 2121 U

USINGSINGCCONTROLONTROLSSTRUCTURES TOTRUCTURES TOMMAKEAKEDDECISIONSECISIONS... 2222 Making

Making Decisions Decisions Using Using If...Then...If...Then...ElseElse... 2222 D

DECIDINGECIDINGBBETWEENETWEENSSEVERALEVERALAALTERNATIVESLTERNATIVES... 2424 Select

Select CaseCase... 2626 U

USINGSINGCCONTROLONTROLSSTRUCTURES TOTRUCTURES TOMMAKEAKECCODEODER R EPEATEPEAT... 2828 Using

Using For...Next For...Next Statement Statement ... 2828 Using

Using For For Each...Next Each...Next Statement...Statement... 3131 Using

Using Do…Loops Do…Loops Statement...Statement... 3232 Using

Using While. While. . . .Wend .Wend Statement...Statement... 3434 P

PUTTING ALL TOGETHER UTTING ALL TOGETHER ... 3535 S

SUBROUTINES ANDUBROUTINES ANDFFUNCTIONUNCTIONPPROCEDURESROCEDURES... ... ... ... ... 3636 W

WHATHATAAREREFFUNCTIONSUNCTIONS? ? ... 3636 S

SUBUBPPROCEDURESROCEDURES... 3636 F

FUNCTIONUNCTIONPPROCEDURESROCEDURES... 3737 D

DECLARINGECLARINGSSUBROUTINESUBROUTINES/F/FUNCTIONSUNCTIONS... 3737 C

CALLING AALLING ASSUBROUTINEUBROUTINE... 3838 C

CALLALLSSTATEMENTTATEMENT... 3939 C

CALLING AALLING AFFUNCTIONUNCTION... 4040 E

EXITING AXITING ASSUBROUTINEUBROUTINE/F/FUNCTIONUNCTION... 4141 P

PASSINGASSINGAARGUMENTS INTORGUMENTS INTOPPROCEDURESROCEDURES... 4141 W

WHYHYAAREREPPROCEDURESROCEDURESUUSEFULSEFUL?? ... 4242 Exit

Exit StatementStatement... 4444 C

CODINGODINGCCONVENTIONSONVENTIONS... ... ... ... ... ... .. 4545 C

CONSTANTONSTANT N NAMINGAMINGCCONVENTIONSONVENTIONS... 4545 V

VARIABLEARIABLE N NAMINGAMINGCCONVENTIONSONVENTIONS... 4646 D

DESCRIPTIVEESCRIPTIVEVVARIABLE ANDARIABLE ANDPPROCEDUREROCEDURE N NAMESAMES... 4646 O

OBJECTBJECT N NAMINGAMINGCCONVENTIONSONVENTIONS... 4646 C

CODEODECCOMMENTINGOMMENTINGCCONVENTIONSONVENTIONS... 4747 F

FUNCTIONS ANDUNCTIONS ANDSSUBUBSSTANDARDSTANDARDS... 4747 Procedure

Procedure Header...Header... 4747 T

THEHEQQUICK UICK TTESTESTEEDITOR DITOR OOPTIONSPTIONS... 4949 Fonts

Fonts and and ColorsColors... 4949 Genera

General...l... 5050 C

CODEODEII NDENTATION NDENTATION... 5050 Q

QUICK UICK TTESTESTR R EUSABLEEUSABLEAACTIONCTIONHHEADER EADER ... 5151 C

CREATING ANREATING ANAACTIONCTIONTTEMPLATEEMPLATE... 5151

VBScript – The Basics

When users interact with computers, they usually get

When users interact with computers, they usually get to some point where theto some point where the computer asks them for information. That i

computer asks them for information. That i nformation is stored or manipulated bynformation is stored or manipulated by the computer in some way. Suppose, for example, that you want to keep a record the computer in some way. Suppose, for example, that you want to keep a record of the number of times the user has clicked the button. In that case, you would of the number of times the user has clicked the button. In that case, you would want to store a value in memory. In any case, you need a "container" in which to want to store a value in memory. In any case, you need a "container" in which to store information. Programmers commonly call

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What is a variable?

A variable is

A variable is a virtual container in the a virtual container in the computer's memory or convenientcomputer's memory or convenient placeholder that refers to a

placeholder that refers to a computer memory location where you can storecomputer memory location where you can store program information that may change during

program information that may change during the time your script is running.the time your script is running. Where the variable is stored i

Where the variable is stored in computer memory is unimportant. What isn computer memory is unimportant. What is

important is that you only have to refer to a variable by name to see or change it important is that you only have to refer to a variable by name to see or change it ss value. In

value. In VBScriptVBScript, variables are always of one fundamental data , variables are always of one fundamental data type,type, Variant.Variant. A computer program can store information in a variable and then access that A computer program can store information in a variable and then access that information later by referring to the variable's name

information later by referring to the variable's name..

Variables Naming Restrictions

Variable names follow the standard rules for naming anything in

Variable names follow the standard rules for naming anything in VBScriptVBScript. A. A variable name:

variable name:

Must begin with an alphabetic character. Must begin with an alphabetic character. Cannot contain an embedded period. Cannot contain an embedded period. Must not exceed 255 characters. Must not exceed 255 characters.

Must be unique in the scope in which it is declared. Must be unique in the scope in which it is declared.

Make sure you never create variables that have the same name as keywords Make sure you never create variables that have the same name as keywords already used by

already used by VBScriptVBScript. These keywords are called reserved words and. These keywords are called reserved words and include terms such as

include terms such as DateDate,, MinuteMinute,, SecondSecond,, TimeTime, and so on., and so on.

How Do I Create a Variable?

When you create a variable, you have to give it a name. That way, when you need When you create a variable, you have to give it a name. That way, when you need to find out what's contained in the variable, you use its name to let the

to find out what's contained in the variable, you use its name to let the computercomputer know which variable you are referring to. You have two ways to create a variable. know which variable you are referring to. You have two ways to create a variable. The first way, called the explicit method, is where you use the

The first way, called the explicit method, is where you use the DimDim keyword to tellkeyword to tell VBScript

VBScript you are about to create a variable. You then follyou are about to create a variable. You then foll ow this keyword with theow this keyword with the name of the variable. If, for example, you want to create a variabl

name of the variable. If, for example, you want to create a variabl e callede called Quantity, you would enter

Quantity, you would enter

Dim

Dim nQuantitynQuantity

And the variable will then exist. And the variable will then exist.

Declaration Statements and Highiligts

Dim Statement

Description

Description The

The DimDim statement declares and allocates storage space in memory forstatement declares and allocates storage space in memory for variables. The

variables. The DimDim statement is used either at the start of a procedure or thestatement is used either at the start of a procedure or the start of a global script block. In the first case, the variable declared using start of a global script block. In the first case, the variable declared using DimDim is local to the procedure. In the second, it's available throughout the module. is local to the procedure. In the second, it's available throughout the module.

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Syntax Syntax

Dim

Dim varnamevarname[([[([subscriptssubscripts])][,])][, varnamevarname[([[([subscriptssubscripts])]] . . .])]] . . . Arguments

Arguments

Parameter Description Parameter Description

varname

varname Name of the variable; follows standard variable naming conventions.Name of the variable; follows standard variable naming conventions. subcripts

subcripts An array and optionally specifies the number and extent oAn array and optionally specifies the number and extent o f arrayf array dimensions up to 60 multiple dimensions may be declared. dimensions up to 60 multiple dimensions may be declared.

Notes Notes

When variables are first initialized with the

When variables are first initialized with the DimDim statement, they have astatement, they have a value of

value of EmptyEmpty. In addition, if a variable ha. In addition, if a variable has been initialized but nots been initialized but not assigned a value, the following expressions will both evaluate to True: assigned a value, the following expressions will both evaluate to True:

If

If vVarvVar == 00 ThenThen If

If vVar = ""vVar = "" ThenThen

Overriding Standard Variable Naming Conventions

You can override standard variable nami

You can override standard variable naming conventions by placing your variableng conventions by placing your variable name in brackets. This all

name in brackets. This allows you to use reserved words or illows you to use reserved words or illegal characters inegal characters in variable names. For example:

variable names. For example:

Dim [Option Explicit] Dim [Option Explicit] [

[Option ExplicitOption Explicit]] = 6= 6 Msgbox

Msgbox [[OptionOptionExplicitExplicit]]

In a common usage, is

In a common usage, is not recommended to use this syntax. However, is not recommended to use this syntax. However, is possible.possible. Those overriding naming convention are useful for user custom classes.

Those overriding naming convention are useful for user custom classes. For more information about classes, in t

For more information about classes, in the advanced topic of he advanced topic of VBScript.VBScript.

Declaring Variables Explicit and Implicit

You declare variables

You declare variables explicitlyexplicitly in your script using thein your script using the DimDim statement, thestatement, the Public

Public statement, and thestatement, and the PrivatePrivate statement.statement.

Dim

Dim nDegreesFahrenheitnDegreesFahrenheit

You declare variables

You declare variables explicitlyexplicitly in your script using thein your script using the DimDim statement, thestatement, the Public

Public statementstatement,, and theand the PrivatePrivate statementstatement..

Dim

Dim nDegreesFahrenheitnDegreesFahrenheit

You declare multiple variables by separating each variable name with a comma. You declare multiple variables by separating each variable name with a comma.

Dim

Dim nTop, nBottom, nLeft, nRightnTop, nBottom, nLeft, nRight

You can also declare a variable

You can also declare a variable implicitlyimplicitly by simply using its name in your script.by simply using its name in your script. That

That is not generally a good practiceis not generally a good practice because you could misspell the variablebecause you could misspell the variable name in one or more

name in one or more places, causing unexpected results when your script is run.places, causing unexpected results when your script is run. For that reason, the

For that reason, the OptionOption ExplicitExplicit statement is available to require explicitstatement is available to require explicit declaration of all variables. The

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statement in your script. statement in your script. For that reason, and for

For that reason, and for coding standards proposes, it is recommended to declarecoding standards proposes, it is recommended to declare variables explicitly, and force other programmers the same by adding the Option variables explicitly, and force other programmers the same by adding the Option Explicit

Explicit statement in the head of any action, reusable action and vbs files.statement in the head of any action, reusable action and vbs files.

Option Explicit Statement

Forces explicit declaration of all variables in a script. Forces explicit declaration of all variables in a script. If used, the

If used, the Option ExplicitOption Explicit statement must appear in a script before any otherstatement must appear in a script before any other statements. When you use the

statements. When you use the Option ExplicitOption Explicit statement, you muststatement, you must explicitlyexplicitly declare all variables using the

declare all variables using the DimDim,, PrivatePrivate,, PublicPublic,, oror ReDimReDim statements. If youstatements. If you attempt to use an undeclared variable name, an error

attempt to use an undeclared variable name, an error occurs likeoccurs like in Figure 1 .in Figure 1 .

Figure 1 – Undefined variable e Figure 1 – Undefined variable error.rror. Tip

Tip Use

Use Option ExplicitOption Explicit to avoid incorrectly typing the name of an existing variable orto avoid incorrectly typing the name of an existing variable or to avoid confusion in code where the scope of the variable is not clear.

to avoid confusion in code where the scope of the variable is not clear. The following example illustrates use of the

The following example illustrates use of the OptionOption ExplicitExplicit statement.statement. Option Explicit

Option Explicit ' Force explicit variable declaration.' Force explicit variable declaration. Dim

Dim MyVarMyVar ' Declare variable.' Declare variable. MyInt = 10

MyInt = 10 ' Undeclared variable generates error.' Undeclared variable generates error. MyVar = 10

MyVar = 10 ' Declared variable does not generate error' Declared variable does not generate error

Working with Arrays

So far you've learned what a variable is, how to create one, and what you can So far you've learned what a variable is, how to create one, and what you can store inside one, a variable containing a single value is a scalar variable. You might store inside one, a variable containing a single value is a scalar variable. You might be wondering if there is some easy way to group variables together in a set.

be wondering if there is some easy way to group variables together in a set. you can create a variable that can contain a series of values. This is called an

you can create a variable that can contain a series of values. This is called an arrayarray variable. Array variables and scalar variables are declared in the same way, except variable. Array variables and scalar variables are declared in the same way, except that the declaration of an array variable uses parentheses ( ) following the variable that the declaration of an array variable uses parentheses ( ) following the variable name. Arrays are useful when you're storing

name. Arrays are useful when you're storing sets of similar data sets of similar data because theybecause they often make it easier to manipulate the data together. If you wanted t

often make it easier to manipulate the data together. If you wanted t o manipulateo manipulate a list of ten coordinates, you would have to execute ten different statements to a list of ten coordinates, you would have to execute ten different statements to handle each one. Besides, how can you be sure you have ten? What if you have handle each one. Besides, how can you be sure you have ten? What if you have only six at the moment? How can your code handle this kind of situation where only six at the moment? How can your code handle this kind of situation where you really don't know ahead of time how many pieces of information you have? you really don't know ahead of time how many pieces of information you have? Here is where the array

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Scalar Variables and Array Variables

The beauty of an array is that it enables you to store and use a series of data The beauty of an array is that it enables you to store and use a series of data using one variable name and an index to distinguish the individual items. By using using one variable name and an index to distinguish the individual items. By using an index, you can often make your code simpler and more efficient so that it's an index, you can often make your code simpler and more efficient so that it's easier for you to put a script together and change it later. With

easier for you to put a script together and change it later. With VBScript,VBScript, thethe elements inside your array can hold any kind of data. The elements don't have to elements inside your array can hold any kind of data. The elements don't have to be all integers or all strings, for example. The array can hold a combination of data be all integers or all strings, for example. The array can hold a combination of data types

types

Creating Arrays

You create arrays using the same

You create arrays using the same keyword you use when creating variablkeyword you use when creating variabl es-thees-the Dim

Dim keyword. An array created with thekeyword. An array created with the DimDim keyword exists as long as thekeyword exists as long as the procedure does and is destroyed once the procedure ends.

procedure does and is destroyed once the procedure ends. If you create the arrayIf you create the array in the main script, outside the procedure, the values will persist as long as the in the main script, outside the procedure, the values will persist as long as the page is loaded.

page is loaded.

You can create two types of arrays using

You can create two types of arrays using VBScriptVBScript: fixed arrays and dynamic: fixed arrays and dynamic arrays. Fixed arrays have a

arrays. Fixed arrays have a specific number of elements in them, whereas dynamicspecific number of elements in them, whereas dynamic arrays can vary in the number of elements depending on how many are stored in arrays can vary in the number of elements depending on how many are stored in the array. Both types of arrays are useful, and both have advantages and

the array. Both types of arrays are useful, and both have advantages and disadvantages.

disadvantages.

Fixed Length Arrays

In the following example, a single-dimension array containing 11 elements is In the following example, a single-dimension array containing 11 elements is declared:

declared:

Dim

Dim arrArray(10arrArray(10))

Although the number shown in the parentheses is 10, all arrays in

Although the number shown in the parentheses is 10, all arrays in VBScriptVBScript areare zero-based, so this array actually contains 11

zero-based, so this array actually contains 11 elements.elements. In a zero-based array, the number of

In a zero-based array, the number of array elements is always the nuarray elements is always the number shownmber shown in parentheses plus one.

in parentheses plus one.

This kind of array is called a fixed-size array. This kind of array is called a fixed-size array.

Dynamic Arrays

The second type of array you can create is the dynamic array. The benefit of a The second type of array you can create is the dynamic array. The benefit of a dynamic array is that if you don't know how large the array will be when you write dynamic array is that if you don't know how large the array will be when you write the code, you can create code that sets or changes the size while the

the code, you can create code that sets or changes the size while the VBScriptVBScript code is running. A dynamic array is created in the same way as a fixed array, but code is running. A dynamic array is created in the same way as a fixed array, but you don't put any bounds in the declaration. As a result, your statement becomes you don't put any bounds in the declaration. As a result, your statement becomes Dim

Dim arrNames()arrNames()

Eventually, you need to tell

Eventually, you need to tell VBScriptVBScript how many elements the array willhow many elements the array will contain.contain. You can do this with the

You can do this with the ReDimReDim functionfunction. ReDim. ReDim tellstells VBScriptVBScript toto "re-dimension""re-dimension" the array to however many el

the array to however many elements you specifyements you specify. ReDim. ReDim takes dimensions thetakes dimensions the same way

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ReDim

ReDim arrName(nCount -arrName(nCount - 11))

So, if you enter So, if you enter ReDim

ReDim arrNames(arrNames(99))

You will create an array that has room to store ten elements. This way, you can You will create an array that has room to store ten elements. This way, you can set the size of the array while the code is running rather than when you write the set the size of the array while the code is running rather than when you write the code. This can be useful when the user gets to decide how many names he will code. This can be useful when the user gets to decide how many names he will enter

enter..

Resizing a dynamic array without Preserve.

To use a dynamic array,

To use a dynamic array, you must subsequently useyou must subsequently use ReDimReDim to determine theto determine the number of dimensions and the size of

number of dimensions and the size of each dimension.each dimension. Dim

Dim arrMyArray()arrMyArray() ReDim

ReDim arrMyArray(arrMyArray(2525)) Redim

Redim arrArray2(arrArray2(10,10,1010,10,10))

Declares dynamic-array variables, and allocates or reallocates storage space at Declares dynamic-array variables, and allocates or reallocates storage space at procedure level.

procedure level. The

The ReDimReDim statement is used to size or resize a dynamic array that has alreadystatement is used to size or resize a dynamic array that has already been formally declared using a

been formally declared using a PrivatePrivate,, PublicPublic, or, or DimDim statement with emptystatement with empty parentheses (without dimension subscripts). You can use the

parentheses (without dimension subscripts). You can use the ReDimReDim statementstatement repeatedly to change the number of elements and dimensions in an array.

repeatedly to change the number of elements and dimensions in an array.

Resizing a dynamic array with Preserve

The

The PreservePreserve keyword is very important when usingkeyword is very important when using ReDim.ReDim. Suppose, forSuppose, for example, that you create a dynamic array, specifying its storage space by

example, that you create a dynamic array, specifying its storage space by usingusing ReDim,

ReDim, fill it with datafill it with data, and then later decide to make it larger so you, and then later decide to make it larger so you can fill itcan fill it with more information without losing your original data.

with more information without losing your original data. In the following example

In the following example, ReDim, ReDim sets the initial size of the dynamic array to 25. Asets the initial size of the dynamic array to 25. A subsequent

subsequent ReDimReDim statement resizes the array to 30, statement resizes the array to 30, but uses thebut uses the PreservePreserve keyword to preserve the contents of the a

keyword to preserve the contents of the a rray as the resizing takes place.rray as the resizing takes place. ReDim

ReDim MyArray(MyArray(2525)) . . .

. . .

ReDim Preserve

ReDim Preserve MyArray(MyArray(3030))

There is no limit to the number of times you can resize a dynamic array, although There is no limit to the number of times you can resize a dynamic array, although if you make an array smaller, you lose the data in the eliminated elements.

if you make an array smaller, you lose the data in the eliminated elements. Figure 3

Figure 3 describes the memory allocations, when using arrays.describes the memory allocations, when using arrays.

Dim

Dim arr(5arr(5))

the system allocates 5 cells in the memory to store the array. This type of the system allocates 5 cells in the memory to store the array. This type of declaration is static; the array size

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Figure 2 – Resizing static arrays Figure 2 – Resizing static arrays

Resize a dynamic array, every time you resize an array without using the keyword Resize a dynamic array, every time you resize an array without using the keyword Preserve, the system allocates a new place in the memory with the required size, Preserve, the system allocates a new place in the memory with the required size, and the last information will be lost.

and the last information will be lost.

Using the keyword preserve, the size of the array will be extended, and the Using the keyword preserve, the size of the array will be extended, and the information will not be lost

information will not be lost

Figure 3 - Memory diagram Figure 3 - Memory diagram

Array Iterations

You can iterate an array using the

You can iterate an array using the For…NextFor…Next statement. The loop isstatement. The loop is based onbased on the array index

the array index

You can iterate an array using the

You can iterate an array using the For Each…NextFor Each…Next statement.statement. More information about loops in

More information about loops in Flow ControlFlow Control

VBScript Constants

Sometimes in writing code, you will want to refer to values that never change Sometimes in writing code, you will want to refer to values that never change .. TheThe values for

values for TrueTrue andand False,False, for example, are always -1 and 0, respectively. Valuesfor example, are always -1 and 0, respectively. Values that never change usually have some special meaning, such as defining

that never change usually have some special meaning, such as defining TrueTrue andand False.

False. These values that never change are called constants. The constantsThese values that never change are called constants. The constants TrueTrue and

and FalseFalse are sometimes referred to as iare sometimes referred to as implicit constants because you do notmplicit constants because you do not need to do anything to reference their constant names. They are immediately need to do anything to reference their constant names. They are immediately available in any code you write.

available in any code you write.

Working with constants

A constant is a variable within a program that never changes in value. Users can A constant is a variable within a program that never changes in value. Users can

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create their own constants by initiali

create their own constants by initiali zing variables accordingly and then notzing variables accordingly and then not changing their value.

changing their value. VBScriptVBScript defines the specialdefines the special TrueTrue andand FalseFalse constants, asconstants, as well.

well.

When you create the simulated

When you create the simulated constant, name the constant with uppercase lettersconstant, name the constant with uppercase letters if the constant represents a value unique to your program. If the constant is a if the constant represents a value unique to your program. If the constant is a special value expected by

special value expected by VBScriptVBScript, prefix the constant name with the letters vb., prefix the constant name with the letters vb. This naming convention is not required, but it will help you distinguish the

This naming convention is not required, but it will help you distinguish the constant from all the other variables.

constant from all the other variables.

See Constant Naming Conventions on page 45 See Constant Naming Conventions on page 45

Declaring constants

Constants perform a similar function to variables, in that they are a symbolic Constants perform a similar function to variables, in that they are a symbolic replacement for an item of data in memory. The difference is that a constant replacement for an item of data in memory. The difference is that a constant keeps the same value throughout its lifetime.

keeps the same value throughout its lifetime.

Constants perform a similar function to variables, in that they are a symbolic Constants perform a similar function to variables, in that they are a symbolic replacement for an item of data in memory. The difference is that a constant replacement for an item of data in memory. The difference is that a constant keeps the same value throughout its lifetime.

keeps the same value throughout its lifetime.

Values are assigned to constants using the same method used for variables, and Values are assigned to constants using the same method used for variables, and can contain the same range

can contain the same range of data subtypes. In most respects, therefore, aof data subtypes. In most respects, therefore, a constant is the same as a variable. In fact, it could be described as a va

constant is the same as a variable. In fact, it could be described as a va riableriable whose value doesn't vary! But because confusion can arise ab

whose value doesn't vary! But because confusion can arise ab out whether you areout whether you are dealing with a constant or a variable wi

dealing with a constant or a variable wi thin the script, it is safest to use a differentthin the script, it is safest to use a different naming convention for constants. The accepted method of denoting

naming convention for constants. The accepted method of denoting a constant isa constant is to use all capitals for the name. In this case, the use of underscores improves their to use all capitals for the name. In this case, the use of underscores improves their readability and is highly

readability and is highly recommended.recommended. You create user-defined constants in

You create user-defined constants in VBScriptVBScript using theusing the ConstConst statement. Usingstatement. Using the

the ConstConst statement, you can create string or statement, you can create string or numeric constants with meaningfulnumeric constants with meaningful names and assign them literal values. For example:

names and assign them literal values. For example:

Const

Const TIMEOUTTIMEOUT == 5454

Const

Const DUE_DATEDUE_DATE == #6-1-97##6-1-97#

Const

Const MY_STRING_CONSTANTMY_STRING_CONSTANT == "Hello World""Hello World"

You may want to adopt a naming

You may want to adopt a naming scheme to differentiate constants from variables.scheme to differentiate constants from variables. This will prevent you from trying to reassign constant values while your script is This will prevent you from trying to reassign constant values while your script is running. For example, you might want to use a "vb" or "con" prefix on your running. For example, you might want to use a "vb" or "con" prefix on your constant names, or you might name your constants in all capital letters. constant names, or you might name your constants in all capital letters. Differentiating constants from variables eliminates confusion as you develop Differentiating constants from variables eliminates confusion as you develop moremore complex scripts.

complex scripts. Remark

Remark

Like the constant declaration in

Like the constant declaration in VB,VB, Const inConst in VBScriptVBScript cannot be used tocannot be used to assignassign non-constant values or the values returned by

non-constant values or the values returned by VBScriptVBScript functions. This meansfunctions. This means that a statement like the following:

that a statement like the following: Const

Const LONG_INT_LEN =LONG_INT_LEN = LenLen(lNum)(lNum) '' Invalid Invalid

Is also invalid, since it attempts to assign the value of a variable to a constant. It Is also invalid, since it attempts to assign the value of a variable to a constant. It also means that a statement like:

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Const

Const LONG_INT_LEN =LONG_INT_LEN = 44 + x+ x '' Invalid Invalid

Is also invalid, since it relies on the value returned by

Is also invalid, since it relies on the value returned by the VBScript Lenthe VBScript Len function.function. Finally, unlike

Finally, unlike VBVB oror VBA,VBA, you are not allowed to use any value whiyou are not allowed to use any value whi ch includes anch includes an operator in defining a constant. For example, the following declaration, which is operator in defining a constant. For example, the following declaration, which is valid in

valid in VBVB, generates a syntax error in, generates a syntax error in VBScript:VBScript: Const

Const ADDED_CONST =ADDED_CONST = 4 + 14 + 1 '' Invalid Invalid

Is also invalid, since it relies on the value returned by

Is also invalid, since it relies on the value returned by the VBScript Lenthe VBScript Len function.function. Finally, unlike

Finally, unlike VBVB oror VBAVBA,, you are not allowed to use any value whiyou are not allowed to use any value whi ch includes anch includes an operator in defining a constant. For example, the following declaration, which is operator in defining a constant. For example, the following declaration, which is valid in

valid in VBVB, generates a syntax error in, generates a syntax error in VBScriptVBScript:: Remark

Remark

Also is possible to declare non decimal values for Constants and variables specially Also is possible to declare non decimal values for Constants and variables specially hexadecimal values, that are so used in programming languages, like:

hexadecimal values, that are so used in programming languages, like:

Const

Const MY_HEXA_CONST =MY_HEXA_CONST = &H02FF&H02FF The statement is legal in

The statement is legal in VBScript,VBScript, alsoalso QuickTestQuickTest, at run-time will transfer, at run-time will transfer thethe value to 767. but there is a syntax checking bug in

value to 767. but there is a syntax checking bug in QuickTestQuickTest that will display thethat will display the follow message:

follow message:

Figure 4 - QuickTest Syntax Error Figure 4 - QuickTest Syntax Error bugbug

VBScript pre-defined constants

A number of useful constants you can use in your code are built into

A number of useful constants you can use in your code are built into VBScriptVBScript.. Constants provide a convenient way to use

Constants provide a convenient way to use specific values without actually havingspecific values without actually having to remember the value itself. Using

to remember the value itself. Using constants also makes your code moreconstants also makes your code more maintainable should the value

maintainable should the value of any constant ever change. Because theseof any constant ever change. Because these constants are already defined in

constants are already defined in VBScriptVBScript, you don't need to explicitly declare, you don't need to explicitly declare them in your code. Simply use them in place of the values they represent. them in your code. Simply use them in place of the values they represent.

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Here are the various categories of constants provided in VBScript and a brief Here are the various categories of constants provided in VBScript and a brief description of each:

description of each:

Color Constants - Defines eight basic colors that

Color Constants - Defines eight basic colors that can be used in can be used in scripting.scripting. Date and Time Constants - Defines date and time constants used by various Date and Time Constants - Defines date and time constants used by various date and time functions.

date and time functions.

Date Format Constants - Defines constants used to

Date Format Constants - Defines constants used to format dates and times.format dates and times. Miscellaneous Constants - Defines constants that don't conveniently fit

Miscellaneous Constants - Defines constants that don't conveniently fit into anyinto any other category.

other category.

MsgBox Constants - Defines constants used in the

MsgBox Constants - Defines constants used in the MsgBoxMsgBox function tofunction to describedescribe button visibility, labeling, behavior, and return values.

button visibility, labeling, behavior, and return values. String Constants - Defines a vari

String Constants - Defines a variety of non-printable characters used in stringety of non-printable characters used in string manipulation.

manipulation.

Tristate Constants - Defines constants used with

Tristate Constants - Defines constants used with functions that formatfunctions that format numbers.

numbers.

VarType Constants - Defines the various Va

VarType Constants - Defines the various Va riant subtypes.riant subtypes. Note

Note

A complete listing of the constant values shown above can be found in

A complete listing of the constant values shown above can be found in VBScriptVBScript Constants topic, on the

Constants topic, on the QuickTest ProfessionalQuickTest Professional Help.Help. More information about

More information about VBScriptVBScript can be found incan be found in Error! Reference source notError! Reference source not found.

found.

The Scope and Lifetime of a Variable

A variable's scope is determined by where you declare it. When you declare a A variable's scope is determined by where you declare it. When you declare a variable within a

variable within a procedure, only code within that procedure can access or changeprocedure, only code within that procedure can access or change the value of that variable. It has local scope and is a

the value of that variable. It has local scope and is a procedure-level variable. If procedure-level variable. If you declare a variable outside a procedure, you make it recognizable to all the you declare a variable outside a procedure, you make it recognizable to all the procedures in your script. This is a

procedures in your script. This is a script-level variable, and it has script-level variable, and it has script-levelscript-level scope.

scope.

The lifetime of a variable depends on how long i

The lifetime of a variable depends on how long i t exists. The lifetime of a script-t exists. The lifetime of a script-level variable extends from the time it is declared until the time the script is level variable extends from the time it is declared until the time the script is finished running. At procedure level, a variable exists only as long as you are in finished running. At procedure level, a variable exists only as long as you are in the procedure. When the procedure exits, the varia

the procedure. When the procedure exits, the varia ble is destroyed. Local variablesble is destroyed. Local variables are ideal as t

are ideal as temporary storage space when a procedure is executing. You can emporary storage space when a procedure is executing. You can havehave local variables of the same name in several different procedures because each is local variables of the same name in several different procedures because each is recognized only by the procedure in which i

recognized only by the procedure in which i t is declared.t is declared.

Private Statement

Description

Description The

The PrivatePrivate statement declares private variables and astatement declares private variables and a llocates storage space.llocates storage space. Declares, in a

Declares, in a ClassClass block, a private variableblock, a private variable.. Syntax

Syntax Private

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Arguments Arguments

varname

Notes Notes

A Private variable's visibility is limited to the script in which it's created for A Private variable's visibility is limited to the script in which it's created for global variables and to the class in which it is declared for class-level

global variables and to the class in which it is declared for class-level variables. Elsewhere, the

variables. Elsewhere, the PrivatePrivate keyword generates an error.keyword generates an error. varname follows standard

varname follows standard VBVB naming conventions. It must begin with annaming conventions. It must begin with an alphabetic character, can't contain embedded periods or spaces,

alphabetic character, can't contain embedded periods or spaces, can't becan't be the same as a

the same as a VBScriptVBScript reserved word, must be shorter than 255reserved word, must be shorter than 255 characters, and must be unique within

characters, and must be unique within its scope.its scope. You can override standard variable

You can override standard variable naming conventions by placing yournaming conventions by placing your variable name in brackets. This allows you to use reserved words or illegal variable name in brackets. This allows you to use reserved words or illegal characters in variable names. For example:

characters in variable names. For example: Private

Private [me][me] Private

Private [1Var][1Var] Private

Private [2-Var][2-Var] Private

Private [Left][Left]

Using the subscripts argument, you can declare up to 60 multiple Using the subscripts argument, you can declare up to 60 multiple dimensions for the array

dimensions for the array..

If the subscripts argument isn't used (i.e., the variable name is followed by If the subscripts argument isn't used (i.e., the variable name is followed by empty parentheses), the array is declared dynami

empty parentheses), the array is declared dynami c. You can change bothc. You can change both the number of dimensions and the number of elements of a dynamic array the number of dimensions and the number of elements of a dynamic array using the

using the ReDimReDim statementstatement.. In

In QuickTest,QuickTest, thethe Public/PrivatePublic/Private Scopes are ignored. Any variable youScopes are ignored. Any variable you declare inside a reusable action will remain

declare inside a reusable action will remain Private.Private. Tips

Tips

All variables created at procedure level (that is, in code within a

All variables created at procedure level (that is, in code within a Sub...EndSub...End Sub, Function...End Function,

Sub, Function...End Function, oror PropertyProperty...EndEnd PropertyProperty construct areconstruct are local by default. That is, they don't have scope outside the procedure in local by default. That is, they don't have scope outside the procedure in which they are created. The use of the

which they are created. The use of the PrivatePrivate keyword in these caseskeyword in these cases generates a runtime error.

generates a runtime error.

You cannot change the dimensions of arrays that were defined to be You cannot change the dimensions of arrays that were defined to be dynamic arrays while preserving their original data.

dynamic arrays while preserving their original data. It's good practice to always use

It's good practice to always use Option ExplicitOption Explicit at the beginning of aat the beginning of a module to prevent misnamed variables from causi

module to prevent misnamed variables from causi ng hard-to-find errors.ng hard-to-find errors.

Public Statement

Description

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The

The PublicPublic statement declares public variables and allocatesstatement declares public variables and allocates storagestorage space.space. Declares, in a

Declares, in a ClassClass block, a private variable.block, a private variable. Syntax

Syntax

Public

Public varnamevarname[([[([subscriptssubscripts])][,])][, varnamevarname[([[([subscriptssubscripts])]] . . .])]] . . . Arguments

Arguments

varname

Notes Notes

The behavior of a

The behavior of a PublicPublic variable depends on where it's declared, as thevariable depends on where it's declared, as the following table shows

following table shows Variable

Variable declared declared in... in... ScopeScope

Any procedure, Function or Property Any procedure, Function or Property statement

statement

Illegal; generates a syntax error; use the Dim Illegal; generates a syntax error; use the Dim statement instead.

statement instead. Global

Global code code (in (in external external vbs vbs file file ) ) Variable Variable is is available available throughout throughout the the script.script. Global code (in a reusable action )

Global code (in a reusable action ) Variable is available throughout the ReusableVariable is available throughout the Reusable action only (Private).

action only (Private). Class block declarations section

Class block declarations section Variable is available as a property of the class toVariable is available as a property of the class to all code within the script.

all code within the script.

varname

varname follows standard VB naming conventions. It must begin with anfollows standard VB naming conventions. It must begin with an alphabetic character, can't contain embedded periods or spaces,

alphabetic character, can't contain embedded periods or spaces, can't becan't be the same as a VBScript reserved word, must be shorter than 255

the same as a VBScript reserved word, must be shorter than 255 characters, and must be unique withi

characters, and must be unique within its scope.n its scope. You can override standard variable

You can override standard variable naming conventions by placing yournaming conventions by placing your variable name in brackets. This allows you to use reserved words or illegal variable name in brackets. This allows you to use reserved words or illegal characters in variable names. For example:

characters in variable names. For example: Public

Public [me][me] Public

Public [1Var][1Var] Public

Public [2-Var][2-Var] Public

Public [Left][Left]

Using the subscripts argument, you can declare up to 60 multiple Using the subscripts argument, you can declare up to 60 multiple dimensions for the array.

dimensions for the array.

If the subscripts argument isn't used (i.e., the variable name is followed by If the subscripts argument isn't used (i.e., the variable name is followed by empty parentheses), the array is declared dynami

empty parentheses), the array is declared dynami c. You can change bothc. You can change both the number of dimensions and the number of elements of a dynamic array the number of dimensions and the number of elements of a dynamic array using the

using the ReDimReDim statementstatement.. In

In QuickTest, the Public/PrivateQuickTest, the Public/Private ScopesScopes are ignored. Any variableare ignored. Any variable youyou declare inside a reusable action will remain

declare inside a reusable action will remain Private.Private. Tips

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Instead of declaring a variable as

Instead of declaring a variable as PublicPublic within a class construct, youwithin a class construct, you should create

should create Property LetProperty Let andand Property GetProperty Get procedures that assignprocedures that assign andand retrieve the value of a private variable, respectively.

retrieve the value of a private variable, respectively.

You cannot change the dimensions of arrays that were defined to be You cannot change the dimensions of arrays that were defined to be dynamic arrays while preserving their original data.

dynamic arrays while preserving their original data. It's good practice to always use

It's good practice to always use Option ExplicitOption Explicit at the beginning of aat the beginning of a module to prevent misnamed variables from causi

module to prevent misnamed variables from causi ng hard-to-find errors.ng hard-to-find errors. To use a global variable, which is not recommended, you can use a

To use a global variable, which is not recommended, you can use a PublicPublic MyVar

MyVar statement on an externalstatement on an external vbsvbs file.file.

To use global variables in your testing suite, use the Environment object, To use global variables in your testing suite, use the Environment object, or/and the global datasheet or a global dictionary pre-defined in the or/and the global datasheet or a global dictionary pre-defined in the repository. For more information see:

repository. For more information see:

QuickTest Professional User's Guide > Creating Tests or Components > Working with Actions > QuickTest Professional User's Guide > Creating Tests or Components > Working with Actions > Sharing Action Information > Sharing Values Using

Sharing Action Information > Sharing Values Using the Dictionary Object the Dictionary Object

VBScript Operators

Arithmetic Operators Arithmetic Operators

Operators used to perform mathematical calculations. Operators used to perform mathematical calculations. Assignment Operator

Assignment Operator

Operator used to assign a value to a property or variable. Operator used to assign a value to a property or variable. Comparison Operators

Comparison Operators Operators used to p

Operators used to perform comparisons.erform comparisons. Concatenation Operators

Concatenation Operators

Operators used to combine strings. Operators used to combine strings. Logical Operators

Logical Operators

Operators used to perform logical

Operators used to perform logical operations.operations.

Working with Operators

As you begin to write

As you begin to write VBScriptVBScript code, you will use operators so much that theircode, you will use operators so much that their use will become natural to you. In this section, you will learn about each of the use will become natural to you. In this section, you will learn about each of the operators available to you in

operators available to you in VBScriptVBScript, as well as how you might go about using, as well as how you might go about using them.

them.

When several operations occur in an expression, each part i

When several operations occur in an expression, each part i s evaluated ands evaluated and resolved in a predetermined order called operator precedence. You

resolved in a predetermined order called operator precedence. You can usecan use parentheses to override the order of precedence and force some

parentheses to override the order of precedence and force some parts of anparts of an expression to be evaluated before others. Operati

expression to be evaluated before others. Operati ons within parentheses areons within parentheses are always performed before those outside. Within

always performed before those outside. Within parentheses, however, standardparentheses, however, standard operator precedence is maintained.

operator precedence is maintained.

When expressions contain operators from more than one category, arithmetic When expressions contain operators from more than one category, arithmetic operators are evaluated first, comparison operators are evaluated next,

operators are evaluated first, comparison operators are evaluated next, and logicaland logical operators are evaluated last. Comparison operators all

operators are evaluated last. Comparison operators all have equal precedence;have equal precedence; that is, they are evaluated in the left-to-right order in which they appear.

that is, they are evaluated in the left-to-right order in which they appear. Arithmetic and logical operators are evaluated in the following order of Arithmetic and logical operators are evaluated in the following order of precedence.

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Arithmetic Operators

The first major class of

The first major class of operators is arithmetic operators. Arithmetic operatorsoperators is arithmetic operators. Arithmetic operators enable you to perform simple

enable you to perform simple arithmetic on one or more variables. Most of arithmetic on one or more variables. Most of thesethese operators will be familiar to you because you have been exposed to them in operators will be familiar to you because you have been exposed to them in everyday life. Few people will be surprised to find, for example, that the + everyday life. Few people will be surprised to find, for example, that the + operator performs addition! Some operators, however, might be new

operator performs addition! Some operators, however, might be new to you. Into you. In any case, you need to understand how to apply these operators to variables and any case, you need to understand how to apply these operators to variables and literals in

literals in VBScriptVBScript code.code.

Operators fit into three separate categories: arithmetic

Operators fit into three separate categories: arithmetic operators, comparisonoperators, comparison operators, and logical operators. Each of these

operators, and logical operators. Each of these categories has a special use in categories has a special use in aa VBScript program. Operators are executed in a

VBScript program. Operators are executed in a specific order when they arespecific order when they are combined. Programmers must take this order into account when they

combined. Programmers must take this order into account when they write code.write code.

Description Symbol Description Symbol Addition Addition ++ Subtraction Subtraction --Multiplication Multiplication ** Division Division / / Integer Division Integer Division \ \ Exponentiation Exponentiation ^^ Modulus arithmetic

Modulus arithmetic ModMod Unary negation

Unary negation --String concatenation String concatenation & &

Table 1 - Arithmetic operators Table 1 - Arithmetic operators

Addition (+)

The first arithmetic operator is the addition operator. You already used this The first arithmetic operator is the addition operator. You already used this operator yesterday and probably intuitively understood its purpose because it operator yesterday and probably intuitively understood its purpose because it is sois so commonly used and easy to understand. The addition operator is used to add commonly used and easy to understand. The addition operator is used to add values, whether they are stored in

values, whether they are stored in variables, constants, or literal numbers. Youvariables, constants, or literal numbers. You also use the +

also use the + operator to concatenate strings.operator to concatenate strings.

Subtraction (-)

This operator works the same way the addition operator does except that it This operator works the same way the addition operator does except that it subtracts one or more numbers rather than add

subtracts one or more numbers rather than add them. Otherwise, the syntax is thethem. Otherwise, the syntax is the same.

same.

Multiplication (*)

Addition and subtraction are important, but you also need to be able to multiply Addition and subtraction are important, but you also need to be able to multiply values together. In most computer languages, the

values together. In most computer languages, the ** symbol is used to indicatesymbol is used to indicate multiplication, not the x symbol.

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Division (/) and Integer Division (\)

The division operator is the

The division operator is the last of the four last of the four commonly used arithmetic operators.commonly used arithmetic operators. Among the common arithmetic operators, division is the

Among the common arithmetic operators, division is the most complicatedmost complicated arithmetic operation a computer performs.

arithmetic operation a computer performs. VBScript has two types of

VBScript has two types of division operators. The first operator handles numbersdivision operators. The first operator handles numbers with decimal points. Usually referred to as the floating-point division operator, it's with decimal points. Usually referred to as the floating-point division operator, it's represented by the / symbol in

represented by the / symbol in code listings.code listings.

The floating-point division operator is designed to divide values with decimal The floating-point division operator is designed to divide values with decimal points, but it can also divide numbers without decimals.

points, but it can also divide numbers without decimals.

Exponentiation (^)

Raises a number to the power of an exponent. Raises a number to the power of an exponent.

Modulus Arithmetic (Mod)

The Mod operator is another p

The Mod operator is another powerful arithmetic operator. Essentially, the Modowerful arithmetic operator. Essentially, the Mod operator returns the remainder after dividing

operator returns the remainder after dividing one number into another.one number into another.

Unary Negation (-)

The last of the arithmetic operators is the negation operator. Simply put, this The last of the arithmetic operators is the negation operator. Simply put, this operator changes the sign of a value contained in a variable or creates a negative operator changes the sign of a value contained in a variable or creates a negative number.

number.

String Concatenation (&)(+)

Forces string concatenation of two expressions. Forces string concatenation of two expressions.

You use the string concatenation operator to merge tw

You use the string concatenation operator to merge two strings together.o strings together.

Comparison Operators

The first set of operators

The first set of operators VBScriptVBScript provides are arithmetic operators. This sectionprovides are arithmetic operators. This section discusses the second type: comparison operators. As the name implies, you use discusses the second type: comparison operators. As the name implies, you use comparison operators to compare one or more variables, numbers, constants, or a comparison operators to compare one or more variables, numbers, constants, or a combination of the three.

combination of the three. VBScriptVBScript has many different types of comparisonhas many different types of comparison operators, and each check for a di

operators, and each check for a different comparison condition.fferent comparison condition.

Description Symbol Description Symbol Equality Equality == Inequality Inequality <><> Less than Less than << Greater than Greater than >> Less than or equal to

Less than or equal to <=<= Greater than or equal to

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Object equivalence

Object equivalence IsIs

Table 2 - Comparison

Table 2 - Comparison OperatorsOperators

Equality (=)

You use the equality operator to see if a variable, constant, or number is equal to You use the equality operator to see if a variable, constant, or number is equal to another. It's common to mistake the equali

another. It's common to mistake the equali ty operator for the assignmentty operator for the assignment operator, which is also represented by an

operator, which is also represented by an equal sign. You use the aequal sign. You use the assignmentssignment operator to set a variable equal to another variable, number, string, constant, or operator to set a variable equal to another variable, number, string, constant, or other data entity. For comparing

other data entity. For comparing strings use thestrings use the StrCompStrComp function.function.

Inequality (<>)

Another important comparison operator is the inequality operator. You

Another important comparison operator is the inequality operator. You use thisuse this operator to test whether a variable is not equal to another variable or some data operator to test whether a variable is not equal to another variable or some data element. For comparing strings use the

element. For comparing strings use the StrCompStrComp function.function.

Less Than (<) and Greater Than (>)

You might have a condition where you don't care whether a variable is equal to You might have a condition where you don't care whether a variable is equal to another, but you do want to know whether it is greater than or less than another another, but you do want to know whether it is greater than or less than another variable, number, or constant. In such a

variable, number, or constant. In such a case, you need the greater-than and lcase, you need the greater-than and l ess- ess-than operators. For comparing strings use the

than operators. For comparing strings use the StrCompStrComp function.function.

Less than or equal (<=), greater than or equal to (>=)

Sometimes, you also might want to see whether a variable is greater than

Sometimes, you also might want to see whether a variable is greater than or equal or equal to

to some other variable, constant, or number. Perhaps you want to know if it issome other variable, constant, or number. Perhaps you want to know if it is lessless than or equal to

than or equal to the entity. Then, you can the entity. Then, you can combine operators to use the less-than-combine operators to use the less-than-or-equal and greater-than-less-than-or-equal operators,

or-equal and greater-than-or-equal operators, <=<= andand >=>=.. For comparing strings use the

For comparing strings use the StrCompStrComp function.function.

Object Equivalence (Is)

The last comparison operator is designed

The last comparison operator is designed for objects.for objects. This operator does not compare one object

This operator does not compare one object to another, nor does it to another, nor does it compare values.compare values. This special operator simply checks to see if the two object references in the

This special operator simply checks to see if the two object references in the expression refer to the same object. Suppose, f

expression refer to the same object. Suppose, f or example, you have assigned aor example, you have assigned a command button in your script. You have

command button in your script. You have another variable,another variable, myObject myObject that is set tothat is set to reference different objects at different points i

reference different objects at different points i n your program. Assume that an your program. Assume that a statement has been carried out that assigns the variable

statement has been carried out that assigns the variable myObject myObject to referenceto reference this button

this button

Logical Operators

The last category of operators in

The last category of operators in VBScriptVBScript is logical operators. The logicalis logical operators. The logical operators might require a more significant

operators might require a more significant amount of understanding to appreciate.amount of understanding to appreciate. In some cases, the way

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intuitive thinking. If you've ever taken a

intuitive thinking. If you've ever taken a course in logic, you have first-handcourse in logic, you have first-hand experience with this.

experience with this.

Because logical operators are such an important part

Because logical operators are such an important part of of VBScriptVBScript in particular,in particular, and every programming language in general, it's important to gain a good and every programming language in general, it's important to gain a good understanding, starting with the basics, so that

understanding, starting with the basics, so that you can use them effectively.you can use them effectively.

Description Symbol

Logical negation

Logical negation NotNot Logical conjunction

Logical conjunction AndAnd Logical disjunction

Logical disjunction OrOr Logical exclusion

Logical exclusion XorXor Logical equivalence

Logical equivalence EqvEqv Logical implication

Logical implication ImpImp

Table 3 - Logical

Table 3 - Logical OperatorsOperators

Logical Negation (Not)

The operator performs logical negation on a

The operator performs logical negation on a n expression. In addition, the Notn expression. In addition, the Not operator inverts the bit values of any variable and sets the corresponding bit operator inverts the bit values of any variable and sets the corresponding bit This operator has the following results

This operator has the following results If

If Expression Expression is is Then Then result result isis

True False True False False True False True Null Null Null Null Bit

Bit Expression Expression is is Bit Bit Result Result isis

0

0 11

1

1 00

Table 4 - Logical Negation Table 4 - Logical Negation

Logical Conjunction (And)

The operator performs a logical

The operator performs a logical conjunction on two expressions.conjunction on two expressions. In order to obtain

In order to obtain TrueTrue in the result variable, bothin the result variable, both expression1expression1 andand expression2expression2 must be

must be TrueTrue. You often use this operator to make sure two or more conditions. You often use this operator to make sure two or more conditions are true before performing some action.

are true before performing some action. If

If Expression1 Expression1 is is And And Expression2 Expression2 is is Then result Then result isis

True

True True True TrueTrue

True

True False False FalseFalse False

False True True FalseFalse False

False False False FalseFalse

If

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0 0 0 0 00 0 0 1 1 00 1 1 0 0 00 1 1 1 1 11 Table 5 - Logical

Table 5 - Logical conjuctionconjuction

Logical Disjunction (Or)

The operator performs a logical disjunction on two expressions.disjunction on two expressions. If either or both expressions evaluate to

If either or both expressions evaluate to TrueTrue,, result result isis TrueTrue.. The

The OrOr operator also performs a bitwise comparison of identically positioned bits inoperator also performs a bitwise comparison of identically positioned bits in two numeric expressions and sets the corresponding bit in

two numeric expressions and sets the corresponding bit in result.result. If

True

True True True TrueTrue

True

True False False TrueTrue False

False True True TrueTrue False

If

If bit bit in in expression1 expression1 is is and and bit bit in in expression2 expression2 is is Then Then result result isis

0 0 0 0 00 0 0 1 1 11 1 1 0 0 11 1 1 1 1 11

Table 6 – Logical Disjunction Table 6 – Logical Disjunction

Logical Exclusion (Xor)

The operator performs a logical exclusion on two expressions.exclusion on two expressions.

The exclusion operator is another in the family of logical operators that you can The exclusion operator is another in the family of logical operators that you can use to make decisions based on the

use to make decisions based on the contents of one or more expressions. It checkscontents of one or more expressions. It checks whether one and only one conditi

whether one and only one condition is exclusivelyon is exclusively TrueTrue.. If

True

True True True FalseFalse True

True False False TrueTrue False

False True True TrueTrue False

If

If bit bit in in expression1 expression1 is is and and bit bit in in expression2 expression2 is is Then Then result result isis

0 0 0 0 00 0 0 1 1 11 1 1 0 0 11