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To get your mind around the concept of productivity, imagine a small, insular farming village in which all of the good land is being farmed and every household grows or makes whatever it uses -- from food to the house itself. Further suppose that a stranger walks into town looking for work.

If you subscribe to the "lump of labor" theory, then this guy is out of luck. The only way he could go to work would be by farming part of someone else's land. If he eats more, someone else must eat less.

But that's not how the world works. Suppose the guy who walks into town has figured out how to build a more effective plow. He can sell his plows to farmers, who will pay for them with a share of their more bountiful harvests. Not only will our stranger have a job, but the farmers will be growing and eating more -- even after paying for their new plows.

Conditional Constructs

Conditional Constructs execute statements or repeat certain set of statements based on conditions.

The following conditional constructs are available in VBScript

· If – Then –Else

· Select Case

f – Then – Else Construct

The If – Then- Else Construct is used to evaluate whether a condition is true or false and depending on the result, to specify one or more statements to execute. Usually the condition is an expression that uses a comparison operator to compare one value or variable with another. The If- Then – Else statements can be nested to as many levels as needed.

For example:

Sub ReportValue(value)
If value = 0 Then
MsgBox value
ElseIf value = 1 Then
MsgBox value
ElseIf value = 2 then
Msgbox value
Else
Msgbox "Value out of range!"
End If

You can add as many ElseIf clauses as you need to provide alternative choices. Extensive use of the ElseIf clauses often becomes cumbersome. A better way to choose between several alternatives is the Select Case statement.

Select Case Construct

The Select-Case structure is an alternative to If Then Else for selectively executing one block of statements from among multiple blocks of statements. The Select Case Construct makes code more efficient and readable.

A Select Case structure works with a single test expression that is evaluated once, at the top of the structure. The result of the expression is then compared with the values for each Case in the structure. If there is a match, the block of statements associated with that Case is executed.

For example:

Select Case Document.Form1.CardType.Options(SelectedIndex).Text

Case "MasterCard"

DisplayMCLogo

ValidateMCAccount

Case "Visa"

DisplayVisaLogo

ValidateVisaAccount

Case "American Express"

DisplayAMEXCOLogo

ValidateAMEXCOAccount

Case Else DisplayUnknownImage PromptAgain

End Select

Iterative Constructs

· Do – Loop

· While – Wend

· For – Next

Do – Loop

The basic difference between a “Do while – Loop” and “Do - Loop while” is that the previous one gets executed only when the condition in the while statement holds true where as a “Do – Loop while” gets executed atleast once, because the condition in the while statement gets checked at the end of the first iteration.

For..Next

For example:

For j = 2 To 10 Step 2

total = total + j

Next

Arrays

An array is a contiguous area in the memory referred to by a common name. It is a series of variables having the same data type. Arrays are used to store related data values. VBScript allows you to store a group of common values together in the same location. These values can be accessed with their reference numbers.

An array is made up of two parts, the array name and the array subscript. The subscript indicates the highest index value for the elements within the array. Each element of an array has a unique identifying index number by which it can be referenced. VBScript creates zero based arrays where the first element of the array has an index value of zero.

Declaring Arrays

· Local Arrays

A local array is available only within the function or procedure, where it is declared.

· Global Arrays

A global array is an array that can be used by all functions and procedures. It is declared at the beginning of the VBScript Code.

The Dim statement is used to declare arrays. The syntax for declaring an array is as follows:

Dim ArrayName(subscriptvalue)

Where, ArrayName is the unique name for the array and SubscriptValue is a numeric value that indicates the number of elements in the array dimension within the array.

Example:

Dim No_Passengers(3)

The No_Passengers can store 4 values.

Assigning values to the array

No_Passengers(1) = 2

No_Passengers(2) = 3

No_Passengers(3) = 4

VBScript provides flexibility for declaring arrays as static or dynamic.

A static array has a specific number of elements. The size of a static array cannot be altered at run time.

A dynamic array can be resized at any time. Dynamic arrays are useful when size of the array cannot be determined. The array size can be changed at run time.

Next we will deal with user defined procedures, functions and subroutines.

Standard maximization problems are special kinds of linear programming problems.

Q Remind me what a linear programming problem is.

A A linear programming (LP) problem is a problem in which we are asked to find the maximum (or minimum) value of a linear objective function

	p = ax + by + cz + ...	Example: p = 3x - 2y + z
Subject to one or more linear constraints of the form
	Ax + By + Cz + . . . (or ) N	Example: x + y - 3z 12

The desired largest (or smallest) value of the objective function is called the optimal value, and a collection of values of x, y, z, . . . that gives the optimal value constitutes an optimal solution. The variables x, y, z, . . . are called the decision variables.

Odd vertex: a vertex that has an odd number of edges emerging from it.

Even vertex: a vertex that has an even number of edges emerging from it.

The Class Model is at the core of object-oriented development and design - it expresses both the persistent state of the system and the behavior of the system. A class encapsulates state (attributes) and offers services to manipulate that state (behavior). Good object-oriented design limits direct access to class attributes and offers services which manipulate attributes on behalf of the caller. This hiding of data and exposing of services ensures data updates are only done in one place and according to specific rules - for large systems the maintenance burden of code which has direct access to data elements in many places is extremely high.

The class is represented as below:

the class has three distinct areas:

Attributes and methods may be marked as