Visual Basic VB: An Introduction

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Visual Basic (VB)An Introduction
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VB History

• Evolved from Beginners All-purpose Symbolic
  Instruction Code (BASIC).
• Introduced at Dartmouth College in the USA by
  Kemeney Kurtz in 1963.
• Designed for beginners, to aid learning computer
  programming.
• Programs execute sequentially.
• In 1975, Bill Gates Paul Allen produced a BASIC
  version for PCs.
• BASIC was the first product sold by the Microsoft
  corporation.

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Cont. VB History

• Visual BASIC was then introduced by Microsoft.
• Aim was to enable software development under
  Windows.
• Event-driven programming language.
• Last version VB6, 1996.
• No VB7.
• Visual Basic .Net 2003, introduced as part of
  Microsofts .Net framework.
• Object-oriented programming language.
• Almost no backward compatibility.

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VB is a 4GL

• 4GLs (fourth-generation languages) are closer to
  human languages than typical high-level
  programming languages.
• 4GLs use graphical paradigm to help developers.
• By contrast
• First generation machine language (0s1s).
• Second generation assembly language
• (LOAD 43, STORE 44).
• Third generation high-level programming
  languages, such as C, C, and Java (xy).

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Why VB in RAD?

• High-level programming language, rich visual
  environment.
• Using VB, quick prototypes can be produced to
  help elicit, refine and prioritise requirements.
• Why not using VB for all projects
• Portability running only on a Microsoft
  operating system.
• Compatibility limited between versions.
• Scalability criticised for not suiting large
  projects.

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VB Event-Driven

• Flow of program execution is determined by users
  actions, interacting with a Graphical User
  Interface (GUI).
• Events can be clicks, changes in text, mouse
  movements, etc.
• Components must programmed to response to user
  events.

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Major Components of a VB Application

• The whole application is called a Project.
• Forms
• Individual windows containing other components,
  i.e. controls
• Controls
• Buttons, text boxes, check boxes, list boxes,
  etc.
• Modules - classes
• Shared instructions, or code.
• Provide much of the underlying functionality of
  the system using Function and Sub procedures
• Event handlers
• Code specific to certain components, not
  necessarily shared.
• Enables the system to react to users actions.
• Invoked (called) automatically by the system when
  an event occurs at the user interface.

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VB Object-oriented

• Most of this programming paradigm is beyond the
  scope of this module.
• However, well mention objects briefly here.
• Even though you wont notice it, you be
  experiencing the basic principles of OO, namely
• Inheritance
• Polymorphism
• Abstraction
• Encapsulation

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The Notion of an Object

• Forms, controls and some other components of a VB
  application are all types of object.
• All these components together to constitute a
  project, from which your executable file is built
  (compiled) to create your app.
• Objects are examples of things. Nouns if you
  like.
• The form, apple, Yussuf Abu-Shaaban, etc.
• An object has a type a class.
• Apple class Fruit.
• Yussuf class Person.
• Objects have characteristics (called attributes
  or properties)
• The form has a colour and a size.
• The apple has an origin, sell by date, colour,
  weight, variety, etc.
• Yussuf has an address, shoe size, a DoB, etc.
• These attributes make objects unique and
  constitute their internal state.

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An Objects Internal State

• Different objects of the same type react in
  different ways to external circumstances,
  depending on their internal state.
• if you are hungry and someone offers you food,
  you will probably accept
• if you are not hungry, you will probably decline.
  
• Your state of hunger determines your response to
  the external stimulus and is often different to
  your friends state.
• For a VB application, each object (form,
  controls, etc.) behaves in different ways
  depending on the events that happen to it, its
  own internal state and the state of the rest of
  the system.
• But what handles these events inside the object?
• For this we need methods.

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The Notion of Methods

• Weve mentioned attributes/properties already as
  being part of objects
• their size, colour, etc.
• But we also have methods that belong to the
  object
• If objects are things (nouns), then methods are
  actions (verbs).
• From the human analogy, our methods are in our
  brain and help us make decisions.
• Methods provide the objects behaviour and
  generally react to events.
• Ask me a question and Ill reply
• Ive got a built-in behaviour (method) that can
  make me reply when I am asked a question.
• Click the submit button and well process your
  order
• So we need a method to process orders after the
  click event.

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Intermediate Recap

• VB applications are made up of a project.
• A project can contain various objects.
• Objects have
• A type (the class or family it belongs to).
• Properties (to provide internal state).
• Methods (to provide behaviour, e.g. change state
  or communicate with other objects).
• Methods respond to events received by the objects.

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Project
State
Type/Class
Properties/ attributes
Has a
Has a
Has
Receives Generates
Object
Events
Affect
Has
Respond to
Arrows imply reading order not data flow
Methods/ Behaviour
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The VB Environment
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The VB Environment

• MS-Visual Studio.Net
• Described as an IDE (Integrated Development
  Environment).
• Handles other languages than just VB.
• Provides a place to
• Develop applications.
• Debug those applications.
• Lots of clever tools here.
• Provides productivity enhancements.
• Automatic completion of property and method names
• Inline highlighting and correction of syntax
  based on context
• Help with documentation
• Etc.

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Events
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The VB Code

• Private Sub RicksTextBox1_TextChanged(...)...
• Me.Text RicksTextBox1.Text
• End Sub
• Notice the indentation!
• Why?
• Well look at Sub, Me, full stops, etc later.
• The labs should give you a flavour.

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The Result
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Variables

• Used to store intermediate results in your
  program.
• The properties/attributes of objects are usually
  variables.
• They are called variables because their values
  may vary as the program runs.
• Each has a name which uniquely identifies it.
• Names should begin with an alphabetic character
  and should contain only alphabetic and numeric
  characters and the underscore (_) character.
• Store a value in each variable, and when you
  access it, it has the same value that you left
  there last time you accessed it.
• Each time you access it, you may look at the
  value it contains, or change the value that it
  contains.

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Declaring Variables

• Variables should be declared before they are
  used.
• The variable declaration specifies the name of
  the variable and its type.
• Just like objects, variables have a type
• The properties we mentioned earlier are generally
  variables
• Dim x As Integer 'whole number eg 78, range
  -2147483648 to 2147483647
• Dim cheese as Long big integer, range much
  bigger 9 x 1018
• Dim y As String 'string of chars, eg "sdffg"
• Dim z As Single 'floating point number eg
  45.678, range gtgt Long
• Dim w As Double 'large floating point number,
  range gtgt Single
• Dim t As Object 'may contain any value
• Dim s As Boolean 'true or false
• Others include Char, Date, Byte, etc.

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Arithmetic Operators

• Enable us to specify calculations which may be
  applied to data.
• Multiply
• / Divide
• Mod Remainder after division
• Add
• - Subtract
• Multiply, divide, and mod are performed before
  plus and minus, unless brackets are used to
  change the order.
• x 437 would leave a value of 25 in x.
• x (43)7 would leave a value of 49 in x.
• x (717)/(24) would leave a value of 4 in x.
• z 11 Mod 3 ' Returns 2.

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Further study

• Read and do the exercises in chapters 1, 2 and 4
  of Bell and Parrs Visual Basic .NET for
  students in the next week.
• Remember, you should be working outside of
  timetabled classes.

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Module Outline