VB SCRIPTING LANGUAGE

VB SCRIPTING LANGUAGE

• VBScript is a scripting language.
• A scripting language is a lightweight programming language.
• VBScript is a light version of Microsoft's programming language Visual Basic.

2.0 Comments

The comment argument is the text of any comment we want to include.
2.0 Purpose of comments:

o   We can use comments for making the script understandable.

o   We can use comments for making one or more statements disable from execution.

2.1 Syntax

Rem comment (After the Rem keyword, a space is required before comment.)

Or

            Apostrophe (') symbol before the comment

2.2 Comment/Uncomment a block of statements

• Select block of statement and use short cut key Ctrl + M (for comment)
• Select comment block and use short cut key Ctrl + Shift + M (for uncomment)

3.0 VB Script Variables

A variable is a convenient placeholder that refers to a computer memory location where we can store program information that may change during the time our script is running.

3.1 Declaring Variables

We declare variables explicitly in our script using the Dim statement, the Public statement, and the Private statement.
 For example:
Dim city
Dim x
We declare multiple variables by separating each variable name with a comma. For example:

Dim x, Top, Bottom, Left, Right

We can also declare a variable implicitly by simply using its name in our script. That is not generally a good practice because we could misspell the variable name in one or more places, causing unexpected results when our script is run. For that reason, the Option Explicit statement is available to require explicit declaration of all variables.
The Option Explicit statement should be the first statement in our script.
3.2 Option Explicit
 Forces explicit declaration of all variables in a script.

Option Explicit   ' Force explicit variable declaration.

Dim MyVar   ' Declare variable.

MyInt = 10   ' Undeclared variable generates error.

MyVar = 10   ' Declared variable does not generate error.

3.3 Naming Restrictions for Variables

Variable names follow the standard rules for naming anything in VBScript. A variable name:

• Must begin with an alphabetic character.
• Cannot contain an embedded period.
• Must not exceed 255 characters.
• Must be unique in the scope in which it is declared.

3.4 Scope of Variables

• A variable's scope is determined by where you declare it.

o   When we declare a variable within a procedure, only code within that procedure can access or change the value of that variable

o   If we declare a variable outside a procedure, we make it recognizable to all the procedures in our script. This is a script-level variable, and it has script-level scope.

3.5 Life Time of Variables

o   The lifetime of a variable depends on how long it exists.

o   The lifetime of a script-level variable extends from the time it is declared until the time the script is finished running.

o   At procedure level, a variable exists only as long as you are in the procedure.

3.6 Assigning Values to Variables

Values are assigned to variables creating an expression as follows:
The variable is on the left side of the expression and the value you want to assign to the variable is on the right.
For example:

B = 200

City = “Hyderabad”

3.7 Scalar Variables and Array Variables

A variable containing a single value is a scalar variable.

A variable containing a series of values, is called an array variable.

Array variables and scalar variables are declared in the same way, except that the declaration of an array variable uses parentheses () following the variable name.

Example:

Dim A(3) 

Although the number shown in the parentheses is 3, all arrays in VBScript are zero-based, so this array actually contains 4 elements.

We assign data to each of the elements of the array using an index into the array. Beginning at zero and ending at 10, data can be assigned to the elements of an array as follows:

A(0) = 256

A(1) = 324

A(2) = 100

A(3) = 55

Similarly, the data can be retrieved from any element using an index into the particular array element you want.
 For example:

SomeVariable = A(4) 

Arrays aren't limited to a single dimension. You can have as many as 60 dimensions, although most people can't comprehend more than three or four dimensions.

Arrays aren't limited to a single dimension. We can have as many as 60 dimensions, although most people can't comprehend more than three or four dimensions.

In the following example, the MyTable variable is a two-dimensional array consisting of 6 rows and 11 columns:

Dim MyTable(5, 10)

In a two-dimensional array, the first number is always the number of rows; the second number is the number of columns.

3.8 Dynamic Arrays 

We can also declare an array whose size changes during the time our script is running. This is called a dynamic array.

The array is initially declared within a procedure using either the Dim statement or using the ReDim statement.
However, for a dynamic array, no size or number of dimensions is placed inside the parentheses.
 For example:

Dim MyArray()

ReDim AnotherArray()

To use a dynamic array, you must subsequently use ReDim to determine the number of dimensions and the size of each dimension.

In the following example, ReDim sets the initial size of the dynamic array to 25. A subsequent ReDim statement resizes the array to 30, but uses the Preserve keyword to preserve the contents of the array as the resizing takes place.

ReDim MyArray(25)

ReDim Preserve MyArray(30)

There is no limit to the number of times we can resize a dynamic array, although if we make an array smaller, we lose the data in the eliminated elements.

4.0 VB Script Data Types

VBScript has only one data type called a Variant. A Variant is a special kind of data type that can contain different kinds of information, depending on how it is used. Because Variant is the only data type in VBScript, it is also the data type returned by all functions in VBScript.

4.1 Variant Subtypes

Beyond the simple numeric or string classifications, a Variant can make further distinctions about the specific nature of numeric information. For example, we can have numeric information that represents a date or a time. When used with other date or time data, the result is always expressed as a date or a time. We can also have a rich variety of numeric information ranging in size from Boolean values to huge floating-point numbers. These different categories of information that can be contained in a Variant are called subtypes. Most of the time, we can just put the kind of data we want in a Variant, and the Variant behaves in a way that is most appropriate for the data it contains.
The following table shows subtypes of data that a Variant can contain.

Subtype	Description
Empty	Variant is uninitialized. Value is 0 for numeric variables or a zero-length string ("") for string variables.
Null	Variant intentionally contains no valid data.
Boolean	Contains either True or False.
Byte	Contains integer in the range 0 to 255.
Integer	Contains integer in the range -32,768 to 32,767.
Currency	-922,337,203,685,477.5808 to 922,337,203,685,477.5807.
Long	Contains integer in the range -2,147,483,648 to 2,147,483,647.
Single	Contains a single-precision, floating-point number in the range -3.402823E38 to -1.401298E-45 for negative values; 1.401298E-45 to 3.402823E38 for positive values.
Double	Contains a double-precision, floating-point number in the range -1.79769313486232E308 to -4.94065645841247E-324 for negative values; 4.94065645841247E-324 to 1.79769313486232E308 for positive values.
Date (Time)	Contains a number that represents a date between January 1, 100 to December 31, 9999.
String	Contains a variable-length string that can be up to approximately 2 billion characters in length.
Object	Contains an object.
Error	Contains an error number.

We can use conversion functions to convert data from one subtype to another. In addition, the VarType function returns information about how your data is stored within a Variant.

5.0 VB Script Operators

Operators are used for performing mathematical, comparison and logical operations.

VBScript has a full range of operators, including arithmetic operators, comparison operators, concatenation operators, and logical operators.

4.1 Operator Precedence

When several operations occur in an expression, each part is evaluated and resolved in a predetermined order called operator precedence.
We can use parentheses to override the order of precedence and force some parts of an expression to be evaluated before others.
Operations within parentheses are always performed before those outside. Within parentheses, however, standard operator precedence is maintained.
When expressions contain operators from more than one category, arithmetic operators are evaluated first, comparison operators are evaluated next, and logical operators are evaluated last.
Comparison operators all have equal precedence; that is, they are evaluated in the left-to-right order in which they appear.
Arithmetic and logical operators are evaluated in the following order of precedence.

4.2 Arithmetic Operators:

Operator	Description
1) Exponentiation Operator (^)	Raises a number to the power of an exponent.
2) Multiplication Operator (*)	Multiplies two numbers.
3) Division Operator (/)	Divides two numbers and returns a floating-point result.
4) Integer Division Operator (\)	Divides two numbers and returns an integer result.
5) Mod Operator	Divides two numbers and returns only the remainder.
6) Addition Operator (+)	Sums two numbers.
7) Subtraction Operator (-)	Finds the difference between two numbers or indicates the negative value of a numeric expression.
8) Concatenation Operator (&)	Forces string concatenation of two expressions.

4.3 Comparison Operators

Used to compare expressions.

Operator	Description	Operator	Description
1) =	Equal to	5) <=	Less than or equal to
2) <>	Not equal to	6) >=	Greater than or equal to
3) <	Less than	7) Is	Object equivalence
4) >	Grater than

 

4.4 Concatenation Operators

Operator	Description
1) Addition Operator (+)	Sums two numbers. If Then 1) Both expressions are numeric Add. 2) Both expressions are strings Concatenate. 3) One expression is numeric and the other is a string Add.
2) Concatenation Operator (&)	Forces string concatenation of two expressions.

4.5 Logical Operators

Operator	Description	Syntax
1) Not	Performs logical negation on an expression.	result= Not expression
2) And	Performs a logical conjunction on two expressions.	result= expression1 And expression2
3) Or	Performs a logical disjunction on two expressions.	result= expression1 Or expression2
4) Xor	Performs a logical exclusion on two expressions.	result= expression1 Xor expression2
5) Eqv	Performs a logical equivalence on two expressions.	result= expression1 Eqv expression2
6) Imp	Performs a logical implication on two expressions.	result= expression1 Imp expression2

6) Input/Output Operations

6.1 InputBox Function

Displays a prompt in a dialog box, waits for the user to input text or click a button, and returns the contents of the text box.

Example:

Dim Input

Input = InputBox("Enter your name") 

MsgBox ("You entered: " & Input)

6.2 MsgBox Function

Displays a message in a dialog box, waits for the user to click a button, and returns a value indicating which button the user clicked.

Example:

Dim MyVar

MyVar = MsgBox ("Hello World!", 65, "MsgBox Example")

   ' MyVar contains either 1 or 2, depending on which button is clicked.

7) VB Script Constants

A constant is a meaningful name that takes the place of a number or string and never changes.

7.1 Creating Constants

We create user-defined constants in VBScript using the Const statement. Using the Const statement, we can create string or numeric constants with meaningful names and assign them literal values.
Const statement
Declares constants for use in place of literal values.
Example:

Const MyString = "This is my string."

Const MyAge = 49

Const CutoffDate = #6-1-97#

Note that String literal is enclosed in quotation marks (" ").

Represent Date literals and time literals by enclosing them in number signs (#).
We declare multiple constants by separating each constant name and value with a comma. For example:
Const price= 100, city= “Hyderabad”, x= 27

8) Conditional Statements

We can control the flow of our script with conditional statements and looping statements.
Using conditional statements, we can write VBScript code that makes decisions and repeats actions. The following conditional statements are available in VBScript:
1) If…Then…Else Statement

2) Select Case Statement 

8.1 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.

If...Then...Else statements can be nested to as many levels as you need.

8.1.1 Running a Statements if a Condition is True (single statement)

To run only one statement when a condition is True, use the single-line syntax for the If...Then...Else statement.

Dim myDate

    myDate = #2/13/98#

    If myDate < Now Then myDate = Now

8.1.2 Running Statements if a Condition is True (multiple statements)

To run more than one line of code, we must use the multiple-line (or block) syntax. This syntax includes the End If statement.

Dim x

x= 20

If x>10  Then

               msgbox "Hello AkhilReddy"

               msgbox "x value is: "&x

               msgbox "Bye Bye"

End If

8.1.3 Running Certain Statements if a Condition is True and Running Others if a Condition is False

We 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.

Example:

Dim x

x= Inputbox (" Enter a value")

If x>100  Then

               Msgbox "Hello AkhilReddy "

               Msgbox "X is a Big Number"

               Msgbox "X value is: "&X

Else 

               Msgbox "AR"

    Msgbox "X is a Small Number"

   Msgbox "X value is: "&X

End If

8.1.4 Deciding Between Several Alternatives

A variation on the If...Then...Else statement allows us to choose from several alternatives. Adding ElseIf clauses expands the functionality of the If...Then...Else statement so we can control program flow based on different possibilities.
Example:

Dim x

x= Inputbox (" Enter a value")

If x>0 and x<=100 Then

               Msgbox "Hello AkhilReddy "

               Msgbox "X is a Small Number"

               Msgbox  "X value is "&x

Else IF x>100 and x<=500 Then

               Msgbox "Hello AR"

               Msgbox "X is a Medium Number"

Else IF x>500 and x<=1000 Then

               Msgbox "Hello AKKI"

               Msgbox "X is a Large Number"

Else 

               Msgbox "Hello Sir"

               Msgbox "X is a Grand Number"

End If

End If

End If

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