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VB Script and QTP - Part1

Going forward, I am starting a series of posts on using VBScript with QTP. It will start from the basics of VB Script and move to the advanced course.

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:

1. Dim Statement
2. Public Statement
3. 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:

1. · Must begin with an alphabetic character.
2. · Cannot contain an embedded period.
3. · Must not exceed 255 characters.
4. · 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 = 49

Note 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.

Next post we will deal with constructs and arrays.