VB Script and QTP - Part2
Conditional Constructs
Conditional Constructs execute statements or repeat certain set of statements based on conditions.
The following conditional constructs are available in VBScript
· If – Then –Else
· Select Case
If – Then – Else Construct
The
If – Then- Else Construct is used to evaluate whether a condition is
true or false and depending on the result, to specify one or more
statements to execute. Usually the condition is an expression that uses
a comparison operator to compare one value or variable with another.
The If- Then – Else statements can be nested to as many levels as
needed.
For example:
Sub
ReportValue(value)If value = 0 Then MsgBox valueElseIf value = 1 Then
MsgBox valueElseIf value = 2 then Msgbox valueElse Msgbox "Value out of
range!"End If
You can add as many ElseIf clauses as you need to provide alternative choices. Extensive use of the ElseIf clauses often becomes cumbersome. A better way to choose between several alternatives is the Select Case statement.
Select Case Construct
The
Select-Case structure is an alternative to If Then Else for selectively
executing one block of statements from among multiple blocks of
statements. The Select Case Construct makes code more efficient and
readable.
A Select Case structure works with a single test
expression that is evaluated once, at the top of the structure. The
result of the expression is then compared with the values for each Case
in the structure. If there is a match, the block of statements
associated with that Case is executed.
For example:
Select Case Document.Form1.CardType.Options(SelectedIndex).Text
Case "MasterCard"
DisplayMCLogo
ValidateMCAccount
Case "Visa"
DisplayVisaLogo
ValidateVisaAccount
Case "American Express"
DisplayAMEXCOLogo
ValidateAMEXCOAccount
Case Else DisplayUnknownImage PromptAgain
End Select
Iterative Constructs
Looping
allows to run a group of statements repeatedly. The loop is repeated
based on a condition. The loop runs as long as the condition is true.
The following looping constructs are available in VBScript.
Do – Loop
While – Wend
· For – Next
Do – Loop
Do
– Loop statements are used to execute a block of statements based on a
condition. The statements are repeated either while a condition is true
or until a condition becomes true. While Keyword can be used to check a
condition in a Do – Loop construct. The condition can be checked before
entering into the loop or after the loop has run at least once.
The
basic difference between a “Do while – Loop” and “Do - Loop while” is
that the previous one gets executed only when the condition in the
while statement holds true where as a “Do – Loop while” gets executed
atleast once, because the condition in the while statement gets checked
at the end of the first iteration.
While – Wend
The
While...Wend statement is provided in VBScript for those who are
familiar with its usage. However, because of the lack of flexibility in
while...wend, it is recommended that you use Do...Loop instead.
For..Next
The
For-Next loop can be used to run a block of statements a specific
number of times. For loops use a counter variable whose value is
increased or decreased with each repetition of the loop. The Step
Keyword is used to increase or decrease the counter variable by the
value that is specified along with it. The For-Next statement can be
terminated before the counter reaches its end value by using the Exit
For statement.
For example:
Dim j, total
For j = 2 To 10 Step 2
total = total + j
Next
MsgBox "The total is " & total
Arrays
An
array is a contiguous area in the memory referred to by a common name.
It is a series of variables having the same data type. Arrays are used
to store related data values. VBScript allows you to store a group of
common values together in the same location. These values can be
accessed with their reference numbers.
An array is made up of
two parts, the array name and the array subscript. The subscript
indicates the highest index value for the elements within the array.
Each element of an array has a unique identifying index number by which
it can be referenced. VBScript creates zero based arrays where the
first element of the array has an index value of zero.
Declaring Arrays
An array must be declared before it can be used. Depending upon the accessibility, arrays are of two types:
· Local Arrays
A local array is available only within the function or procedure, where it is declared.
· Global Arrays
A
global array is an array that can be used by all functions and
procedures. It is declared at the beginning of the VBScript Code.
The Dim statement is used to declare arrays. The syntax for declaring an array is as follows:
Dim ArrayName(subscriptvalue)
Where,
ArrayName is the unique name for the array and SubscriptValue is a
numeric value that indicates the number of elements in the array
dimension within the array.
Example:
Dim No_Passengers(3)
The No_Passengers can store 4 values.
Assigning values to the array
No_Passengers(0) = 1
No_Passengers(1) = 2
No_Passengers(2) = 3
No_Passengers(3) = 4
Static and Dynamic Arrays:
VBScript provides flexibility for declaring arrays as static or dynamic.
A static array has a specific number of elements. The size of a static array cannot be altered at run time.
A
dynamic array can be resized at any time. Dynamic arrays are useful
when size of the array cannot be determined. The array size can be
changed at run time.
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