VBScript- VBScript (visual Basic Scripting) is scripting language developed by Microsoft for windows operating systems.
A VBScript code must be executed within a host environment. It allows you to interact with the host environment to perform some Programming tasks.
Internet Explorer (IE) - allows you to include VBScript code in HTML documents to be executed while IE is rendering HTML Documents.
Windows Script Host (WSH) - Allows you to include VB Script code in Script files to be executed directly on the windows operating system.
VBScript is actually is a limited variation of Microsoft's Visual Basic programming language. Therefore VBScript shares the same language syntax as Visual Basic
VARIABLES
Like many other programming languages, Visual Basic (VB) uses variables to reserve memory to store data and to name that memory location.
A variable must be declared with a name and a specific data type.
Example.
1. Explicit Declaration - A variable is declared with the "Dim" statement in the following syntax:
Dim variable_name As data_type
Where “Variable_name” is name of the variable and data_type data type for variable.
2. Implicit Declaration - A variable name is used on the left side of an assignment statement without
Being declared previously. The data type of an implicitly declared variable is "Variant
Assigning Values to Variables
variable_name = data_value. Value=8;
Variable_name is name of the variable
Data value is value assigned to the variable.
Numeric Comparisons
Numeric comparisons are operations that:
Operates on two numeric operands.
Produces a Boolean value by applying the comparison operation specified
a. Equal to (=): Resulting (True) if two operands are numerically equal.
b. Not equal to (<>): Resulting (True) if two operands are numerically not equal.
c. Greater than (>): Resulting (True) if the first operand is numerically greater than the second operand.
d. Less than (<): Resulting (True) if the first operand is numerically less than the second operand.
e. Greater than or equal to (>=): Resulting (True) if the first operand is numerically greater than or equal to the second operand.
f. Less than or equal to (<=): Resulting (True) if the first operand is numerically less than or equal to the second operand .
Math Built-In Functions
Abs(vNumber) - Returns the absolute value of a specified number
Atn(vNumber) - Returns the arctangent of a specified number
Cos(vNumber) - Returns the cosine of a specified number (angle)
Exp(vPower) - Returns e raised to a power
Hex(vNumber) - Returns the hexadecimal value of a specified number
Int(vNumber) - Returns the integer part of a specified number
Fix(vNumber) - Returns the integer part of a specified number
Log(vNumber) - Returns the natural logarithm of a specified number
Conditional Statements
Using conditional statements, you can write VBScript code that makes decisions and repeats actions. The following conditional statements are available in VBScript:
- If...Then...Else statement
- Select Case statement
Making Decisions Using If...Then...Else
The If...Then...Else statement is used to evaluate whether a condition is True or False and, depending on the result, to specify one or more statements to run. Usually the condition is an expression that uses a comparison operator to compare one value or variable with another. For information about comparison operators, see Comparison Operators. If...Then...Else statements can be nested to as many levels as you need.
Running Statements if a Condition is True
To run only one statement when a condition is True, use the single-line syntax for the If...Then...Else statement. The following example shows the single-line syntax. Notice that this example omits the Else keyword.
Sub FixDate()
Dim myDate
myDate = #2/13/95#
If myDate < Now Then myDate = Now
End Sub
To run more than one line of code, you must use the multiple-line (or block) syntax. This syntax includes the End If statement, as shown in the following example:
Sub AlertUser(value)
If value = 0 Then
AlertLabel.ForeColor = vbRed
AlertLabel.Font.Bold = True
AlertLabel.Font.Italic = True
End If
End Sub
Running Certain Statements if a Condition is True and Running Others if a Condition is False
You can use an If...Then...Else statement to define two blocks of executable statements: one block to run if the condition is True, the other block to run if the condition is False.
Sub AlertUser(value)
If value = 0 Then
AlertLabel.ForeColor = vbRed
AlertLabel.Font.Bold = True
AlertLabel.Font.Italic = True
Else
AlertLabel.Forecolor = vbBlack
AlertLabel.Font.Bold = False
AlertLabel.Font.Italic = False
End If
End Sub
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.
The following looping statements are available in VBScript:
- Do...Loop: Loops while or until a condition is True.
- While...Wend: Loops while a condition is True.
- For...Next: Uses a counter to run statements a specified number of times.
- For Each...Next: Repeats a group of statements for each item in a collection or each element of an array.
Using Do Loops
You can use Do...Loop statements to run a block of statements an indefinite number of times. The statements are repeated either while a condition is True or until a condition becomes True.
Repeating Statements While a Condition is True
Use the While keyword to check a condition in a Do...Loop statement. You can check the condition before you enter the loop (as shown in the following ChkFirstWhile example), or you can check it after the loop has run at least once (as shown in the ChkLastWhile example). In the ChkFirstWhile procedure, if myNum is set to 9 instead of 20, the statements inside the loop will never run. In the ChkLastWhile procedure, the statements inside the loop run only once because the condition is already False.
Sub ChkFirstWhile()
Dim counter, myNum
counter = 0
myNum = 20
Do While myNum > 10
myNum = myNum - 1
counter = counter + 1
Loop
MsgBox "The loop made " & counter & " repetitions."
End Sub
Sub ChkLastWhile()
Dim counter, myNum
counter = 0
myNum = 9
Do
myNum = myNum - 1
counter = counter + 1
Loop While myNum > 10
MsgBox "The loop made " & counter & " repetitions."
End Sub
Repeating a Statement Until a Condition Becomes True
There are two ways to use the Until keyword to check a condition in a Do...Loop statement. You can check the condition before you enter the loop (as shown in the following ChkFirstUntil example), or you can check it after the loop has run at least once (as shown in the ChkLastUntil example). As long as the condition is False, the looping occurs.
Sub ChkFirstUntil()
Dim counter, myNum
counter = 0
myNum = 20
Do Until myNum = 10
myNum = myNum - 1
counter = counter + 1
Loop
MsgBox "The loop made " & counter & " repetitions."
End Sub
Sub ChkLastUntil()
Dim counter, myNum
counter = 0
myNum = 1
Do
myNum = myNum + 1
counter = counter + 1
Loop Until myNum = 10
MsgBox "The loop made " & counter & " repetitions."
End Sub
Exiting a Do...Loop Statement from Inside the Loop
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.
In the following example, myNum is assigned a value that creates an endless loop. The If...Then...Else statement checks for this condition, preventing the endless repetition.
Sub ExitExample()
Dim counter, myNum
counter = 0
myNum = 9
Do Until myNum = 10
myNum = myNum - 1
counter = counter + 1
If myNum < 10 Then Exit Do
Loop
MsgBox "The loop made " & counter & " repetitions."
End Sub
Using 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.
Using For...Next
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.
The following example causes a procedure called MyProc to execute 50 times. The For statement specifies the counter variable x and its start and end values. The Next statement increments the counter variable by 1.
Sub DoMyProc50Times()
Dim x
For x = 1 To 50
MyProc
Next
End Sub
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.
Sub TwosTotal()
Dim j, total
For j = 2 To 10 Step 2
total = total + j
Next
MsgBox "The total is " & total
End Sub
To decrease the counter variable, use a negative Step value. You must specify an end value that is less than the start value. In the following example, the counter variable myNum is decreased by 2 each time the loop repeats. When the loop is finished, total is the sum of 16, 14, 12, 10, 8, 6, 4, and 2.
Sub NewTotal()
Dim myNum, total
For myNum = 16 To 2 Step -2
total = total + myNum
Next
MsgBox "The total is " & total
End Sub
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.
Using For Each...Next
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.
Sub cmdChange_OnClick
Dim d 'Create a variable
Set d = CreateObject("Scripting.Dictionary")
d.Add "0", "Athens" 'Add some keys and items
d.Add "1", "Belgrade"
d.Add "2", "Cairo"
For Each I in d
Document.frmForm.Elements(I).Value = D.Item(I)
Next
End Sub
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