Structure Of Programming Languages

STRUCTURE OF PROGRAMMING LANGUAGES

VISUAL BASIC .NET

CONTENTS:

1. What is Visual Basic .NET?

3. Visual Basic .NET User Interface 5. Visual Basic .NET Versions 7. Operating Visual Basic .NET 9. Visual Basic .NET Controls 11.Keywords, Functions and Statements

VISUAL BASIC .NET §VISUAL BASIC (VB), FORMERLY CALLED THE VISUAL BASIC .NET (VB .NET), IS AN OBJECT ORIENTED COMPUTER PROGRAMMING LANGUAGE THAT CAN BE VIEWED AS AN EVOLUTION OF MICROSOFT’S VISUAL BASIC (VB) IMPLEMENTED ON THE MICROSOFT .NET

VISUAL BASIC START UP PAGE

VISUAL BASIC USER INERTFACE

SYSTEM REQUIREMENT: DEVELOPER : MICROSOFT

OPERATING SYSTEM : MIROSOFT WINDOWS , MS-DOS

VERSIONS OF VISUAL BASIC .NET §Visual Basic .NET §Visual Basic .NET 2003 (VB 7.1) §Visual Basic 2005 (VB 8.0) §Visual Basic 2008 (VB 9.0) §Visual Basic 'VBx' (VB 10.0)

OPERATING THE VISUAL BASIC SURROUNDING AND CREATING PROGRAMS

There's a lot happening on the start page. But basically, this is where you can start a new project, or open an existing one. The first Tab, Projects, is selected. At the moment, the area labelled "Open an Existing Project" is blank. This is what you'll see when you run the software for the first time (because you haven't created a project yet). When you create a project, the Name you gave it will be displayed on this page, as a hyperlink. Clicking the link will open the project.

At the bottom of the screen, there are two buttons: "New Project" and "Open Project". To get started, click the "New Project" button. When you do, you'll see this dialogue box appear:

As a beginner, you'll normally want the option selected: "Windows Application", in the "Visual Basic Projects" folder. This means that you're going to be designing a programme to run on a computer running the Microsoft Windows operating system. If you look in the Name textbox at the bottom, you'll see it says "WindowsApplication1". This is the default name for your projects. It's not a good idea to keep this name. After all, you don't want all of your projects to be called "WindowsApplication1", "WindowsApplication2",

Click the OK button, and the Visual Basic NET design time environment will open. It will look like the following (the 2008 edition is just the same):

In the Visual Basic NET design time environment, the first thing to concentrate on is that strange, big square in the top left. That's called a form. It's actually the pretty bit of your programme, the part that others will see when they launch your masterpiece. Granted, it doesn't look too attractive at the moment, but you'll soon discover ways to lick it into shape. To run the form, try this:

From the menu bar, click Debug From the drop down menu, click Start Alternatively, press the F5 key on your keyboard Your programme is launched

You have now created your very first programme. It should look like this:

Click the Red X on the form to stop it from running. You will then be returned to the software environment.

Be aware that there's a two step process to VB programming: designing and debugging §Design Time is where you get to play about with the form, spruce it up, add textboxes, and buttons, and labels (and code, of course ) §Debug is where you can test your programme and see how well it performs.

Things like buttons, textboxes, and labels are all things that you can add to your Forms. They are know as Controls, and are kept in the Toolbox for ease of use. The Toolbox can be found on the left of the screen. In the picture below, you can see the toolbox icon next to Form1:

To display all the tools, move your mouse over the toolbox icon. You'll see the following automatically appear:

There are seven categories of tools available. The toolbox you'll be working with first is the Common Controls toolbox. To see the tools, click on the plus symbol next to Common Controls. You'll see a long list of tools:

Let's start by adding a textbox to our form. With the tools displayed, do the following: Locate the TextBox tool Double click the icon A textbox is added to your form The textbox gets added to the top left position of your form. To move it down, hold your mouse over the textbox and drag to a new position:

Notice the small squares around the textbox. These are sizing handles. Move your mouse over one of them. The mouse pointer turns into an extended line with arrowheads. Hold your left mouse button down and drag outwards. The textbox is resized. Play around with the sizing handles until you're happy with the size of your textbox.

One thing you will notice is that you can't make the size any higher, but you can make it wider. The reason why you can't make it any higher is because the default action of a textbox is to have it contain only a single line of text. If it's only going to contain one line of text, Microsoft reasoned, there's no reason why you should be

Create two more textboxes by double clicking on the textbox icon in the toolbar (Or Right-click on the selected textbox and choose Copy. Then Right-click on the Form and choose Paste.) Resize them to the same size as your first one Line them up one below the other with space in between Try to create something that looks like the one

Let's add some labels near the textboxes so that your users will know what they are for. Locate the label control in the toolbox Double click the label icon A new label is added to your form It should look like the one below

Click on the label to select it. Now hold your left mouse button down on the label. Keep it held down and drag it to the left of the textbox.

Create two more labels, and position them to the left of the textboxes. You should now have a form like this one:

To see what your Form looks like as a programme, click Debug > Start from the menu bar. Or press F5 on your keyboard:

To stop the programme from running, you can do one of the following: 1. Click the Red X at the top right of your Form 2. Click Debug > Stop Debugging from the menu bar 3. Press Shift + F5 on your keyboard

You can also click the Stop button on the VB toolbars at the top, as in the image below:

SAMPLE PROGRAM FOR VISUAL BASIC .NET (VB .NET) Public Class Form1 Inherits System.Windows.Forms.Form [Windows Form Designer generated code] Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load MessageBox.Show("Hello World!") End Sub End Class OUTPUT; ‘ HELLO WORLD ‘ Press F5 or go to the Debug menu and select Start to start the program. You should see an alert box that says "Hello World!" and then the main window (with nothing on it) should open. Click the "X" in the title bar like you would to quit any program!

VISUAL BASIC .NET CONTROLS

Visible Controls Textboxes A TextBox is used to get and display text. A TextBox can only display text in one font, so it can't be used for word processing. By default, a TextBox will only display text on a single line. If you require more than one line you can set it's Multiline property to true. •Passwords If you need a TextBox for accepting a password you should set it's PasswordChar property to a character. The character you choose will be displayed in the TextBox instead of what is actually typed. Good characters to choose include * and ●. •Clipboard You can copy the selected text to the clipboard by using the TextBox.Copy method. Use the TextBox.Paste method to paste text into the Textbox from the

Labels Labels are used to display text. Unlike the textbox, it is not meant to accept input from the user. Often a Label is used to describe another control, and is often used as a prompt for a Textbox.label display read-only text as far as the user is concerned. Buttons Buttons are controls that are usually raised that the user most often can click on to perform some action defined by the programmer. Once the programmer has added the button control to a form, he can define an event handler to perform an action when the button is clicked. Checkboxes A check box indicates a two-way choice or state (true/false) which can be edited by the user. Check boxes are shown on the screen as a square box that can contain white space (for false) or a check mark (for true). Adjacent to the check box is normally shown a caption describing the meaning of the check box. Inverting the state of a check box is done by clicking the mouse

Radio Buttons A radio button allows the user to choose exactly one of a predefined set of options. Radio buttons are arranged in groups of two or more and displayed on screen a list of circular holes that can contain white space (for unselected) or a dot (for selected). Each radio button can show a caption describing the choice that this radio button represents. This is done by setting the radio button's text property.

RichTextBox Can easily save Richtext files with Colours and Fonts. Has all the qualities of a textbox but with built in save method(richtextbox1.savefile(pathname)) and openfile(Richtextbox1.openfile(filename)).

Other controls not visible at design time

OpenFileDialog An OpenFileDialog displays the standard "Open" dialog. It lets the user browse for a file. SaveFileDialog A SaveFileDialog displays the standard "Save" dialog. It lets the user browse for a directory to save files and enter a filename. It can (optionally) automatically append extensions to the filename. FontDialog A FontDialog lets the user to select a font from a list of installed fonts. ColorDialog A ColorDialog lets the user select predefined color or specify a custom color. Timer Control A Timer Control is a control that will execute code at intervals. It is not visible at runtime. The interval can be set in the properties in the measurement of milliseconds. The timer control will continue to

Comparative Samples

The following simple example demonstrates similarity in syntax between VB and VB.NET. Both examples pop up a message box saying "Hello, World" with an OK button.

Classic

VB example:

Private Sub Command1_Click() MsgBox "Hello, World" End Sub

A

VB.NET example:

Public Class Form1 Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click MessageBox.Show("Hello, World") End Sub End Class

Obsolete Keywords, Functions, and Statements in VB .NET Keyword, Function or Statement §Array

•Circle, Line §Currency §MsgBox

§String

Keyword, Function or Statement •Type •String Functions

Variant

Disposition

New Keywords, Functions, and Statements in VB .NET Class §IsArray

§Short, CShort

§^=, *=, /=, \=, +=, -=, &=

§MyClass

Class §Namespace

§DirectCast

§IsReference

Disposition

END OF PRESENTATION BY: aLjoN