VBScript is a subset of the Visual Basic Programming language.
The result of the slimming down process is a very small language
that is easy to use. JavaScript can do all that VBScript
can do and far more. So why use VBScript instead of JavaScript?
Because VBScript is much easier to learn than JavaScript.
Visual Basic for Applications (VBA) is another subset of
the Visual Basic Programming language for use with Microsoft
Word, Excel, Access etc. While it contains a good many freatures
not supported by VBScript, the basic syntax, or construction
of the language, is very similar.
Syntax
A variable is a virtual container in the computer's memory
that's used to hold information. In concept, it is much the
same as a notepad. You can jot down information on the page
of a notepad and return to that specific page later to remember
what you wrote or modify the information. A computer program
can store information in a variable and then access that
information later by referring to the variable's name.
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 computer know which
variable you are referring to. You have two ways to create
a variable. For example, you want to create a variable called
Quantity, you would enter:
| |
Dim Quantity
'To assign a value to the variable quantity use:
Quantity
= 5
|
A control structure is a combination of keywords in code
used to make a decision that alters the flow of code the
computer executes.
If…Then
The first control structure you should know about is If…Then.
The syntax for this control structure is given as:
| |
If condition
= True Then
...the code that executes if the condition is satisfied
End If
|
where condition is some test you want to apply to
the conditional structure. If the condition is true, the
code within the If and End
If statements is executed. If the condition is not
true, the code within these statements is skipped over and
does not get executed.
If…Then…Else
What if you want to do one thing if the condition is true
but another thing if the condition is false? You could use
two statements:
| |
If condition
= True Then
Msgbox "The condition is true!"
End If
If condition = False Then
Msgbox "The condition is false!"
End If
|
but wouldn't it be nice if you didn't have to repeat the test Fortunately,
you have another control structure available to you in VBScript that makes
this process easier. The control structure, called If…Then…Else,
is represented as
| |
If condition
= True Then
...this is the code that executes if the condition is satisfied
Else
...this is the code that executes if the condition is not satisfied
End If
|
ElseIf
What if you had a few other cases you wanted to test? You're
in luck: You can do as many tests as you want by simply placing ElseIf statements
between the first If statement and the End If statement.
The syntax of such a structure looks like this:
| |
If condition1
= True Then
...the code that executes for condition1
ElseIf condition2 = True Then
...the code that executes for condition2
ElseIf condition3 = True Then
...the code that executes for condition3
Else
...the code that executes if none of the above are true
End If
|
Select Case
What if you have to perform a large number of tests on the
same expression? The Select statement often makes your code
easier to read and interpret than would a long list of Else and Else
If statements. The Select Case structure is defined
as follows:
| |
Select
Case test_expression
Case expression-1
...this is the code that executes if expression-1 matches test_expression
Case expression-2
...this is the code that executes if expression-2 matches test_expression
Case expression-3
...this is the code that executes if expression-3 matches test_expression
Case Else
...this is the code that executes if expression-n matches test_expression
End Select
|
Consider an example in which you want to print a message
to the user based on what state the user lives in:
| |
Select
Case State
Case "Michigan"
Message = "Michigan is a wonderful state to visit if you enjoy fresh-water
lakes."
Case "Virginia"
Message = "Visit the Commonwealth for a wide variety of historical landmarks
and beautiful mountain-scapes."
Case "Arizona"
Message = "Arizona is a wonderful getaway for those who love heat with low
humidity" Case "Colorado"
Message = "Colorado is almost unsurpassed for its majestic mountains and rivers."
Case Else Message = "No specific information
is available about this state."
End Select
|
On occasion, you will need to write code that repeats some
set of statements. Oftentimes, this will occur when you need
to perform some calculation over and over or when you have
to apply the same calculations or processing to more than
one variable. This section shows you all the control structures
you can use in VBScript to control code in your program that
repeats.
For…Next
The first structure is often referred to as the For…Next loop.
The syntax for this structure is
| |
For counter
= start to finish
...code that gets repeated
Next
|
For Example the following code will display a message box
on the screen displaying the current value of x as it increments
from 5 to 50.
| |
For counter
= 1 to 10
x = x + 5
msgbox x
Next
|
Do While…Loop
The basic syntax for this structure is
| |
Do
While condition
...code within the loop goes here
Loop
|
where the condition is either true or false. As long as
the condition is true, the code within the loop gets executed.
Once the condition becomes false, the loop stops and the
code after the loop is executed. The only way for the program
to break out of the loop is if the condition becomes false
or if an Exit Do statement is encountered somewhere inside
the loop. Consider the following example:
| |
Again = True
DoubleIt = 1
' Keep doubling the number as long as the user desires
Do While Again = True
' Show current results and prompt to see if we should continue
If MsgBox("Current total is " & DoubleIt & ". Double it again ?", vbYesNo)
= vbYes Then
DoubleIt = DoubleIt * 2
Else
Again = False
End If
Loop
|
In this example, the first line of code sets the variable
that gets tested in the loop equal to true. The second line
sets the initial value of the variable that gets doubled
to one. Setting the loop variable ("Again") equal
to true allows the loop to begin running because the third
line says, "If Again is true, enter the loop." The first
statement in the loop displays the result to the user.
Because nothing has been doubled yet, the result is one-the
initial value of the DoubleIt variable. When the results
are displayed, the user is asked if they want to continue.
If they choose to go forward, the variable DoubleIt is multiplied
by two. When the program hits the Loop instruction, it will
return to the top of the loop and once again check to see
if the condition is set to true. Because the condition has
not changed, the loop executes again. It will continue to
execute until the user chooses not to continue. Once that
happens, the variable Again is set to False.
Now, when Loop is reached, the code swings back up to the
top of the loop and evaluates the condition once more. This
time, the condition is false, so the loop does not execute
again. The code moves on beyond the loop.
Do Until…Loop
This is very similar to the Do While…Loop except that rather
than perform the operations within the loop while the condition
is true, it executes the operations inside the loop until
the condition is true. The Do
Until…Loop structure takes the form
| |
Do
Until condition
...code within the loop goes here
Loop
|
| Category |
Omitted Feature/Keyword |
| Array Handling |
Option Base
Declaring arrays with lower bound <> 0 |
| Collection |
Add, Count, Item, Remove
Access to collections using ! character (e.g., MyCollection!Foo) |
| Conditional Compilation |
#Const
#If...Then...#Else |
| Control Flow |
DoEvents
GoSub...Return, GoTo
On Error GoTo On...GoSub, On...GoTo
Line numbers, Line labels |
| Conversion |
CVar, CVDate Str, Val |
| Data Types |
All intrinsic data types except Variant Type...End
Type |
| Date/Time |
Date statement, Time statement |
| DDE |
LinkExecute, LinkPoke, LinkRequest, LinkSend |
| Debugging |
Debug.Print
End, Stop |
| Declaration |
Declare (for declaring DLLs)
Optional
ParamArray
Static |
| Error Handling |
Erl
Error
Resume, Resume Next |
| File Input/Output |
All traditional Basic file I/O |
| Financial |
All financial functions |
| Object Manipulation |
TypeOf |
| Objects |
Clipboard
Collection |
| Operators |
Like |
| Options |
Deftype
Option Base
Option Compare
Option Private Module |
| Select Case |
Expressions containing Is keyword or any comparison
operators Expressions containing a range of values using
the To keyword. |
| Strings |
Fixed-length strings
LSet, RSet
Mid Statement
StrConv |
| Using Objects |
Collection access using ! |
Related Links
Microsoft's
scripting pages.
|
