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Declaring Variables
You declare variables explicitly in your script using the
Dim statement, the Public
statement, and the Private
statement. For example:
Dim DegreesFahrenheit
You declare multiple variables by separating each
variable name with a comma. For example:
Dim Top, Bottom, Left, 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.
Naming Restrictions
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.
Scope and Lifetime of Variables
A variable's scope is determined by where you declare it.
When you declare a variable within a procedure, only code
within that procedure can access or change the value of that
variable. It has local scope and is a procedure-level
variable. If you declare a variable outside a procedure, you
make it recognizable to all the procedures in your script.
This is a script-level variable, and it has script-level
scope.
The lifetime of a variable depends on how long it exists.
The lifetime of a script-level variable extends from the
time it is declared until the time the script is finished
running. At procedure level, a variable exists only as long
as you are in the procedure. When the procedure exits, the
variable is destroyed. Local variables are ideal as
temporary storage space when a procedure is executing. You
can have local variables of the same name in several
different procedures because each is recognized only by the
procedure 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.
You 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(10) = 55
Similarly, the data can be retrieved from any element
using an index into the particular array element you want.
For example:
. . .
SomeVariable = A(8)
. . .
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. You can
declare multiple dimensions by separating an array's size
numbers in the parentheses with commas. 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.
You can also declare an array whose size changes during
the time your 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 you can resize a
dynamic array, although if you make an array smaller, you
lose the data in the eliminated elements.
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