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VB Script – A Widely Used Scripting Language

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What we learn last session?

Branching

Branching using If…Then…Else statement.

Branching using Select Case

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Subjects for session 5

Looping through code.

Do…Loop

While…Wend

For…Next

For…Each

Exit statement.

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Looping Through Code

Looping allows you to run a group of statements repeatedly.

Some loops repeat statements until a condition is False;

others repeat statements until a condition is True.

There are also loops that repeat statements a specific number of times.

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Do While/Until

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Looping Through Code Using Do…Loop Statement

Repeats a block of statements while a condition is True or until a condition becomes True.

The following looping statements are available in VBScript:

Do [{While | Until} condition]    [statements]    [Exit Do]    [statements]

Loop

Do [{While | Until} condition]    [statements]    [Exit Do]    [statements]

Loop

Do    [statements]   [Exit Do]    [statements]

Loop [{While | Until} condition]

Do    [statements]   [Exit Do]    [statements]

Loop [{While | Until} condition]

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Looping Through Code Using Do…Loop Statement

You can exit a Do...Loop by using the Exit Do statement.

Because you usually want to exit only in certain situations, such as to avoid an endless loop, you should use the Exit Do statement in the True statement block of an If...Then...Else statement.

If the condition is False, the loop runs as usual.

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Looping Through Code Using Do…Loop Statement

Dim bCheck, Count

bCheck = True : iCount = 0 ' Initialize variables.

Do ' Outer loop.

Do While iCount < 20 ' Inner loop.

iCount = iCount + 1 ' Increment Counter.

If iCount = 10 Then ' If condition is True...

bCheck = False ' set value of flag to False.

Exit Do ' Exit inner loop.

End If

Loop

Loop Until bCheck = False ' Exit outer loop immediately.

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Looping Through Code Using While…Wend Statement

Executes a series of statements as long as a given condition is True.

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.

The While...Wend statement is provided in VBScript for those who are familiar with its usage.

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Looping Through Code Using For…Next Statement

Repeats a group of statements a specified number of times.

You can use For...Next statements to run a block of statements a specific number of times.

For loops, use a counter variable whose value increases or decreases with each repetition of the loop

Dim x For x = 1 To 50

MyProc Next

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Looping Through Code Using For…Next Statement

Using the Step keyword, you can increase or decrease the counter variable by the value you specify.

In the following example, the counter variable j is incremented by 2 each time the loop repeats.

When the loop is finished, the total is the sum of 2, 4, 6, 8, and 10.

Dim j, itotal For j = 2 To 10 Step 2

itotal = itotal + j Next Msg = "The total is " & itotal

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Looping Through Code Using For…Next Statement

You can exit any For...Next statement before the counter reaches its end value by using the Exit For statement.

Because you usually want to exit only in certain situations, such as when an error occurs, you should use the Exit For statement in the True statement block of an If...Then...Else statement.

If the condition is False, the loop runs as usual.

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A For Each...Next loop is similar to a For...Next loop.

Instead of repeating the statements a specified number of times, a For Each...Next loop repeats a group of statements for each item in a collection of objects or for each element of an array.

This is especially helpful if you don't know how many

elements are in a collection.

Looping Through Code Using For Each...Next Statement

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Looping Through Code Exit Statement

Exits a block of Do...Loop, For...Next, Function, or Sub code.

Exit Do

Provides a way to exit a Do...Loop statement.

It can be used only inside a Do...Loop statement.

Exit For

Provides a way to exit a For loop.

It can be used only in a For...Next or For Each...Next loop.

Exit Function

Immediately exits the Function procedure in which it appears.

Exit Property

Immediately exits the Property procedure in which it appears.

Exit Sub

Immediately exits the Sub procedure in which it appears.