The book you need to succeed! Vbscript, jscript

24
 Part 
I
 
Getting Started with Windows Scripting
Comparison operators
When you perform comparisons, you check for certain conditions, such as whether A is greater than 
B, or if A is equal to C. You primarily use comparison operators with conditional statements, such as 
If Then
 and 
If Then Else
. The available operators are summarized in Table 2-7.
TABLE 2-7
Comparison Operators in VBScript
Operator
Description
=
Equality; evaluates to True if the values are equal.
<>
Inequality; evaluates to True if the values are not equal.
<
Less than; evaluates to True if value1 is less than value2.
<=
Less than or equal to; evaluates to True if value1 is less than or equal to value2.
>
Greater than; evaluates to True if value1 is greater than value2.
>=
Greater than or equal to; evaluates to True if value1 is greater than or equal to value2.
Listing 2-3 shows how you can use comparison operators in a script. Note that you can use these 
operators to compare numbers as well as strings and that there is no set precedence order for com-
parisons. Comparisons are always performed from left to right.
LISTING 2-3
Scripting with Comparison Operators
checktotal.vbs
currTotal = 519
prevTotal = 321
if currTotal = 0 Then
  WScript.Echo “The total is zero.”
End If
if currTotal = prevTotal Then
  WScript.Echo “The totals are
    equal.”
End If
if currTotal <> 0 Then
  WScript.Echo “The total does NOT
    equal zero.”
End If
if currTotal <> prevTotal Then
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25
 VBScript 
Essentials 
2
  WScript.Echo “The totals are NOT
    equal.”
End If
if currTotal < 0 Then
  WScript.Echo “The total is less
    than zero.”
End If
if currTotal > 0 Then
  WScript.Echo “The total is
    greater than zero.”
End If
if currTotal <= prevTotal Then
  WScript.Echo “currTotal is less
    than or equal to prevTotal.”
End If
if currTotal >= 0 Then
  WScript.Echo “The total is
    greater than or equal to zero.”
End If
Output
The total does NOT equal zero.
The totals are NOT equal.
The total is greater than zero.
The total is greater than or equal
One other comparison operator you should learn about is the special operator 
Is
. You use 
Is
 to 
compare objects, such as buttons. If the objects are of the same type, the result of the comparison is 
True
. If the objects are not of the same type, the result of the comparison is 
False
. You can test to 
see if the object 
theButton
 references the VBScript object 
Button
 as follows:
Answer = theButton Is Button
If Answer = True Then
   WScript.Echo “theButton is equivalent to Button.”
Else
   WScript.Echo “theButton is NOT equivalent to Button.”
End If
You can also perform the comparison directly in an 
if
 statement:
If theButton Is Button Then
   WScript.Echo “theButton is equivalent to Button.”
Else
   WScript.Echo “theButton is NOT equivalent to Button.”
End If
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26
 Part 
I
 
Getting Started with Windows Scripting
Performing operations on strings
The most common string operations you’ll want to perform are assignment and concatenation. You 
assign values to strings using the equals sign, ensuring that the value is enclosed in double quota-
tion marks, such as:
aString = “This is a String.”
Concatenation is the technical term for adding strings together. Although you can use the 
+
 operator 
to concatenate strings, the normal operator for string concatenation is the 
&
 operator. Using the 
&
 
operator, you can add strings together as follows:
custAddress = streetAdd & “ “ & cityState & “ “ & zipCode
Sometimes you may also want to display the value of a string in a message box. In such an instance, 
you will use the 
&
 operator as well. For example:
aString = “I get it!”
WScript.Echo “The string value is: “ & aString
would display a dialog box with the message:
The string value is: I get it!
Conditional Statements
Traffic lights control the flow of traffic on the street. Conditional instructions control the flow of 
instructions in your code.
Using If…Then
You use 
If
 statements to execute a set of instructions only when certain conditions are met. In 
VBScript, 
If…Then
 structures follow this syntax:
If condition = True Then
  ‘Handle the condition
End If
or
If condition Then
   ‘Handle the condition
End If
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27
 VBScript 
Essentials 
2
Note the use of the 
End If
 statement. This is what makes it possible to execute multiple commands 
when a condition exists, such as:
If sum > 25 Then
   WScript.Echo “The sum exceeds the expected Result”
   ‘Reset sum to zero
   sum = 0
End If
You can control the execution of instructions based on a false condition as follows:
If condition = False Then
  ‘The condition is false
End If
or
If Not condition Then
  ‘The condition is false
End If
Using Else and ElseIf
You can extend the 
If
…
Then
 condition with 
Else
 statements. The 
Else
 statement provides an alter-
native when a condition that you specified is not met. The structure of an 
If
…
Then Else
 statement 
is as follows:
If checkValue = “Yes” Then
   WScript.Echo “The condition has been met.”
Else
   WScript.Echo “The condition has not been met.”
End If
To add more conditions, you can use 
ElseIf
 statements. Each additional condition you add to the 
code is then checked for validity. An example using 
ElseIf
 is shown in Listing 2-4.
LISTING 2-4
Working with ElseIf
testvalue.vbs
currValue = 5
If currValue < 0 Then
  WScript.Echo “The value is less than zero.”
ElseIf currValue = 0 Then
  WScript.Echo “The value is equal to zero.”
continued
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