Starting Out with Visual Basic.NET 2 nd Edition Chapter 1 Introduction to Programming and Visual Basic.NET

Starting Out with Visual Basic .NET 2nd EditionStarting Out with Visual Basic .NET 2nd Edition

Chapter 1

Introduction to Programming and Visual Basic .NET


1.1Introduction

Starting Out with Visual Basic .NET 2nd Edition

With Visual Basic .NET, You May

• Create applications with graphical windows, dialog boxes, menus, and so on

• Create applications that work with databases

• Create web applications and applications that use internet technologies

• Create applications that display graphics


1.2Computer Systems:

Hardware and Software

All Computer Systems Consist of Similar Hardware Devices and

Software Components


Organization of a Computer System

CentralProcessing

Unit

MainMemory

InputDevice

OutputDevice

SecondaryStorage


The CPU

• Fetches instructions

• Carries out the operations commanded by the instructions

• Produces some outcome or resultant information

• The instructions are part of a program stored as binary numbers


Main Memory

• Commonly known as RAM (Random Access Memory)

• Consists of sequentially numbered storage locations

• In most contemporary computers, each location can store 8 bits, called a byte

• RAM is normally a volatile storage medium


Secondary Storage

• A nonvolatile storage medium

• Will hold data without the computer being turned on

• Usually a disk drive (magnetic storage)• Hard disks• Floppy disks


Input Devices

• A device that receives information from the outside world• Keyboard• Mouse• Scanner


Output Devices

• Sends information from the computer to the outside world• Display• Printer


Software

• Programs that run the computer

• Operating System Software: a set of programs that manages the computer's hardware devices (e.g. Windows 2000)

• Application Software: a program that makes the computer useful to the user (e.g. Word, computer games, Internet browsers)


1.3Programs and Programming

Languages

A Program Is a Set of Instructions a Computer Follows in Order to Perform a Task

A Programming Language Is a Special Language Used to Write Computer Programs


What Is a Program?, I

1. Display a message on the screen: "How many hours did you work?"

2. Allow the user to enter the number of hours worked

3. Once the user enters a number, store it in memory

4. Display a message on the screen: "How much do you get paid per hour?"

5. Allow the user to enter an hourly pay rate


What Is a Program?, II

6. Once the user enters a number, store it in memory

7. Once both the number of hours worked and the hourly pay rate are entered, multiply the two numbers and store the result in memory

8. Display a message on the screen that shows the amount of money earned. The message must include the result of the calculation performed in step 7


Common Programming Languages

• BASIC• FORTRAN• COBOL

• Pascal• C• C++• Java


Methods of Programming

• Procedural• Constructed as a set of procedures

(operational, functional units)

• Object-Oriented• Constructed as a set of objects• Objects have data elements and perform actions


Example of an Object

• This is a GUI object

• Data includes number-of-hours-worked, hourly-pay-rate, and gross-pay-earned

• Action is to calculate and display gross-pay- earned, given number-of-hours-worked and hourly-pay-rate


Event Driven Programming: Events

• An event is an action that takes place within a program, such as the clicking of a control

• All Visual Basic .NET controls are capable of detecting various events


Event Driven Programming: Procedures

• For every event, there must be an event procedure

• You will write Visual Basic .NET code that will instruct the computer what actions to take whenever a specific event is triggered


1.4More About Controls and

Programming

As a Visual Basic .NET Programmer, You Must Design and Create the Two Major Components of an Application: the GUI

Elements (Forms and Other Controls) and the Programming Statements That Respond to And/or Perform Actions (Event

Procedures)


Visual Basic .NET Controls

• As a Windows Operating System user, you are already familiar with many of these controls:• Label - A box that displays text• RadioButton - A round button that can be

selected or not with the mouse• Form - A window with other controls within it


Other Visual Basic .NET Controls

• CheckBox• ComboBox• Button• GroupBox

• HScrollBar• ListBox• TextBox• VScrollBar


Name Property

• All of the controls have Properties

• Each Property has a value (or values)

• Every control has a Name Property

• The value of the Name Property is what it is called in programs• The value of the name property of one of the

authors of this book is: Tony


Examples of Names, I

btnCalcGrossPay btnClose

txtHoursWorked

txtPayRate

lblGrossPay

Label1Label2

Label3


Examples of Names, II

• Names like Label1 are default names generated by Visual Basic .NET

• Others are programmer specified using a naming convention:• txt… for Text Boxes

• lbl… for Labels

• btn… for Buttons


Gross Pay Calculation Code

Private Sub btnCalcGrossPay_Click(ByVal sender As System.Object, _

ByVal e As System.EventArgs) Handles btnCalcGrossPay.Click

Dim grossPay As Single

‘ The next line calculates the gross pay.

grossPpay = Val(txtHoursWorked.Text) * Val(txtPayRate.Text)

lblGrossPay.Text = FormatCurrency(grossPay)

End Sub


Close Code

Private Sub btnClose_Click(ByVal sender As System.Object, _

ByVal e As System.EventArgs) Handles btnClose.Click

‘ End the application.

End

End Sub


Language Elements

• Keywords: Words with special meaning to Visual Basic .NET (e.g., Private, Sub)

• Programmer-defined-names: Names created by the programmer (e.g., grossPay)

• Operators: Special symbols to perform common operations (e.g.: +, -, *, and /)

• Remarks: Comments inserted by the programmer - not part of the running program


Language Elements: Syntax

• Syntax means how things are formed

• The syntax of Visual Basic .NET specified how the Language Elements can be combined to form a valid program

• The syntax of the English Language defines how sentences are formed from the parts of speech (nouns, verbs, etc.)


1.5The Programming Process

The Programming Process Consists of Several Steps, Which Include Design,

Creation, Testing, and Debugging Activities


Step 1 of Developing an Application

• Clearly define what the program is to do• For example:

• Purpose: To calculate the user’s gross pay

• Input: Number of hours worked, hourly pay rate

• Process: Multiply number of hours worked by hourly pay rate (The result is the user’s gross pay)

• Output: Display a message indicating the user’s gross pay



• Visualize the application running on the computer and design its user interface



• Make a list of the controls needed• Partial list:

Type Name DescriptionTextBox txtHoursWorked Allows the user to enter the number of hours worked.TextBox txtPayRate Allows the user to enter the hourly pay rateLabel lblGrossPay Displays the gross pay, after the btnCalcGrossPay

button has been clickedButton btnCalcGrossPay When clicked, multiplies the number of hours worked

by the hourly pay rateButton btnClose When clicked, terminates the application



• Define the Values of Each Control's Relevant Properties:

Control Type Control Name TextForm (Default) "Wage Calculator"Label (Default) "Number of Hours Worked"Label (Default) "Hourly Pay Rate"Label (Default) "Gross Pay Earned"Label lblGrossPay "$0.00"TextBox txtHoursWorked ""TextBox txtPayRate ""Button btnCalcGrossPay "Calculate Gross Pay"Button btnClose "Close"



• Make a list of methods needed for each control:

Method DescriptionbtnCalcGrossPay_Click Multiplies the number of hours worked by the

hourly pay rateThese values are entered into thetxtHoursWorked and txt-PayRate TextBoxesThe result is stored in the lblGrossPay Textproperty

btnClose_Click Terminates the application



• Create a pseudocode version of each method:• Pseudocode is a combination of English and a programming language• For this application:

Store Number of Hours Worked times Hourly Pay Rate in grossPay.Store the value in grossPay in lblGrossPay.Text.



• Check the code for errors:• Go step by step through the code, running it in your

head as though the computer is running it

• Keep track of where in the code is being executed

• Keep track of the values of all of the variables



• Use Visual Basic .NET to create the forms and other controls identified in step 3• This is the first use of Visual Basic .NET, all of the

previous steps have just been on paper



• Use Visual Basic .NET to write the code for the event procedures and other methods created in step 6• This is the second step on the computer



• Attempt to run the application - find syntax errors• Correct any syntax errors found and repeat this step as

often as necessary

• All of the syntax errors must be removed before Visual Basic .NET will create a program that you can actually run on the computer



• Run the application - once all syntax errors are fixed• Run the program with a variety of test data

• Check the results to be sure that they are correct

• Correct any errors found

• Repeat steps 10 and 11 as many times as necessary


1.6Visual Studio and the

Visual Basic .NET Environment

Visual Studio Consists of Tools That You Use to Build Visual Basic .NET

Applications


The Visual Basic .NET Environment, I

• Design Window

• Solution Explorer Window

• Dynamic Help Window

• Properties Window

• Docked and Floating Windows

• Title Bar


The Visual Basic .NET Environment, II

• Menu Bar

• Standard Toolbar

• Layout Toolbar

• Toolbox

• Using Tooltips

Documents

Starting Out with Visual Basic.NET 2 nd Edition Chapter 1 Introduction to Programming and Visual Basic.NET