What is VBScript?
VBScript
is a subset of Visual Basic 4.0 language. It was developed by Microsoft
to provide more processing power to Web pages. VBScript can be used to
write both server side and client side scripting. (If you already know
Visual Basic or Visual Basic for Applications (VBA), VBScript will be
very familiar. Even if you do not know Visual Basic, once you learn
VBScript, you are on your way to programming with the whole family of
Visual Basic languages.)
Data types
VBScript
supports only one data type called ‘Variant’. The variant data type is
a special kind of data type that can contain different kinds of
information. It is the default data type returned by all functions in
VBScript. A variant behaves as a number when it is used in a numeric
context and as a string when used in a string context. It is possible
to make numbers behave as strings by enclosing them within quotes.
Variables
A
variable is a placeholder that refers to a memory location that stores
program information that may change at run time. A variable is referred
to by its name for accessing the value stored or to modify its value.
Variable Declaration
Variables in VBScript can be declared in three ways:
Dim Statement
Public Statement
Private Statement
For example:
Dim No_Passenger
Multiple variables can be declared by separating each variable name with a comma. For example:
Dim Top, Left, Bottom, Right
You
can also declare a variable implicitly by simply using its name in your
script. That is not generally a good practice because you could
misspell the variable name in one or more places, causing unexpected
results when your 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 your script.
Note:
Variables declared with Dim
at the script level are available to all procedures within the script.
At the procedure level, variables are available only within the
procedure.
Public statement variables are available to all procedures in all scripts.
Private statement variables are available only to the script in which they are declared.
Naming Convention
There are standard rules for naming variables 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.
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
Scalar Variables and Array Variables
Much
of the time, you only want to assign a single value to a variable you
have declared. A variable containing a single value is a scalar
variable. Other times, it is convenient to assign more than one related
value to a single variable. Then you can create a variable that can
contain a series of values. This 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. In the following example, a
single-dimension array containing 11 elements is declared:
Dim
A(10)Although the number shown in the parentheses is 10, all arrays in
VBScript are zero-based, so this array actually contains 11 elements.
In a zero-based array, the number of array elements is always the
number shown in parentheses plus one. This kind of array is called a
fixed-size array.
Constants
A
constant is a meaningful name that takes the place of a number or a
string, and never changes. VBScript in itself has a number of defined
intrinsic constants like vbOK, vbCancel, vbTrue, vbFalse and so on.
You
create user-defined constants in VBScript using the Const statement.
Using the Const statement, you can create string or numeric constants
with meaningful names and assign them literal values. For example:
Const
MyString = "This is my string."Const MyAge = 49Note that the string
literal is enclosed in quotation marks (" "). Also note that constants
are public by default.
Within procedures, constants are always private; their visibility can't be changed.
|