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Control Structures
Control structures allow you to control the flow of execution of your scripts.
You can specify that some code should be executed only under certain
circumstances, using conditional structures. You can specify that some code
should be executed repeatedly, using looping structures. Lastly, you can
specify that code from somewhere else in the script should be executed using
branching controls.
Conditional Structures
The If...Then...Else construct allows you to choose which block of code to
execute based on a condition or series of conditions.
<%
If condition1 Then
codeblock1
ElseIf condition2 Then
codeblock2
Else
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codeblock3
End If
%>
If condition1 is true, codeblock1 is executed. If it is false, and condition2 is
true, codeblock 2 is executed. If condition1 and condition2 are both false,
codeblock3 executes. An If-Then construct may have zero or more ElseIf
statements, and zero or one Else statements.
In place of some really complex If ...Then constructs, you can use a Select
Case statement. It takes the following form:
Select Case variable
Case choice1
codeblock1
Case choice2
codeblock2
Case choicen
codeblockn
Case default
default code block
End Select
This compares the value of variable with choicel, choice2, and so on. If it
finds a match, it executes the code associated with that choice. If it does not, it
executes the default code.
Looping Structures
Looping structures allow you to execute the same block of code repeatedly.
The number of times it executes may be fixed or may be based on one or
more conditions.
The For...Next looping structure takes the following form:
For counter = start to stop
codeblock
Next
codeblock is executed with counter having the value start, then with counter
having the value start+1, then start+2, and so forth through the value stop.
Optionally, you may specify a different value to increment counter by. In this
case the form looks like this:
For counter = start to stop Step stepvalue
codeblock
Next
Now counter will take the values start+stepvalue, start+stepvalue+stepvalue,
and so forth. Notice that if stepvalue is negative, stop should be less than start.
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The For Each...Next looping structure takes the following form:
For Each item In Set
codeblock
Next
codeblock is executed with item taking the value of each member of Set. Set
should be an array or a collection.
The Do While-Loop looping structure has the following form:
Do While booleanValue
code block
codeblock is executed as long as booleanValue is True. If it is False to begin
with, the loop is not executed at all.
The While...Wend looping structure has the following form:
While booleanValue
codeblock
Wend
codeblock is executed as long as booleanValue is True. If it is False to begin
with, the loop is not executed at all.
The Do-Loop While looping structure has the following form:
Do
code block
Loop While booleanValue
codeblock is executed as long as booleanValue is True. The loop is executed
at least once no matter what.
The Do Until-Loop looping structure has the following form:
Do Until booleanValue
codeblock
code block is executed as long as booleanValue is false. If it is true to begin
with, the loop is not executed at all.
The Do...
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Do
code block
Loop Until booleanValue
code block is executed as long as booleanValue is false. The loop is executed
at least once no matter what.
Branching Structures
Branching structures allow you to jump from one position in the code to
another. A subroutine does not return a value. It simply executes. Subroutines
look like this:
Sub name (argumentlist)
code block
End Sub
Functions do return values and have the following form:
Function name (argumentlist)
code block
name = expression
End Function
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