Computer Programming - Visual Basic

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Computer Studies Chapter 1 Introduction to the Visual Basic Language and Environment

Transcript of Computer Programming - Visual Basic

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Computer StudiesChapter 1

Introduction to the Visual BasicLanguage and Environment

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W hat is Visual Basic?

a tool that allows you to developWindows (Graphic User Interface - GU I)

applications.It is event-driven, meaning code remainsidle until called upon to respond to some

event (button pressing, menu selection, ...).It is governed by an event processor.

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Event Processor

Once an event is detected, the codecorresponding to that event (event procedure)is executed. Program control is then returnedto the event processor.

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Some Features of Visual Basic

Sequential and random access file supportUseful debugger and error-handling facilities

Powerful database access toolsActiveX supportPackage & Deployment Wizard makes

distributing your applications simple

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Visual Basic 6.0 versus Other Versionsof Visual Basic

The original Visual Basic for DOS and VisualBasic For Windows were introduced in 1991.

Visual Basic 3.0 - 1993.Visual Basic 4.0 - 1995 (added 32 bitapplication support).

Visual Basic 5.0 - 1996. New environment,supported creation of ActiveX controls,deleted 16 bit application support.

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S tructure of a Visual Basic Application

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Application (Project) is made up of:

Methods - Built-in procedure that can be invokedto impart some action to a particular object.Event Procedures - Code related to some object.This is the code that is executed when a certainevent occurs.G eneral Procedures - Code not related to objects.This code must be invoked by the application.Modules - Collection of general procedures,variable declarations, and constant definitionsused by application.

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S teps in Developing Application

1. Draw the user interface2. Assign properties to controls

3. Attach code to controls

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Drawing the U ser Interface andS etting Properties

Visual Basic operates in three modes. ± Design mode - used to build application ± R

un mode - used to run the application ± Break mode - application halted and debugger is

available

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Main W indow

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Form W indow

Is central to developing Visual Basicapplications. It is where you draw yourapplication.

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Toolbox

Is theselectionmenu forcontrols usedin yourapplication.

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Properties W indow

is used toestablishinitialpropertyvalues forobjects.

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Form Layout W indow

shows where (uponprogram execution)your form will bedisplayed relative toyour monitor sscreen:

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Project W indow

displays a list of all forms andmodulesmaking up yourapplication.

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Exercise 1Hello World!

Create a simple program that will displayHello World! using Visual Basic

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Exercise 2S topwatch Application - Drawing

Controls

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A Brief History of BasicLanguage developed in early 1960's atDartmouth College

± B (eginner's) ± A (All-Purpose) ± S (Symbolic) ± I (Instruction) ±

C (Code)Answer to complicated programming languages(FORTRAN, Algol, Cobol ...).First timesharelanguage.

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A Brief History of Basic

In the mid-1970's, two college students writefirst Basic for a microcomputer (Altair) - cost$350 on cassette tape. You may have heard of them: Bill Gates and Paul Allen!Every Basic since then essentially based onthat early version. Examples include: GW-Basic, QBasic, QuickBasic.Visual Basic was introduced in 1991.

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Visual Basic S tatements and

ExpressionsThe simplest statement is the assignmentstatement. It consists of a variable name,followed by the assignment operator (=),followed by some sort of expression.Examples:

± Start T ime = Now ± Explorer.Caption = "Captain Spaulding" ± BitCount = ByteCount * 8 ± Energy = Mass * LIGH TSPEE D ^ 2 ± NetWorth = Assets - Liabilities

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Comment statements

begin with the keyword R em or a single quote(')Example

Rem T his is a remark' T his is also a remarkx = 2 * y ' another way to write a remark or comment

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Visual Basic Operators

Operator Operation^ Exponentiation

* / Multiplication and division\ Integer division (truncates)Mod Modulus

+ - Addition and subtractionParentheses around expressions can change

precedence.

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Comparison operatorsOperator Comparison> Greater than< Less than> = Greater than or equal to<= Less than or equal to= Equal to<> Not equal toThe result of a comparison operation is a

Boolean value ( True or False).

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Logical operators

Operator OperationNot Logical not

And Logical andOr Logical orT he Not operator simply negates an operand.T

he And operator returns aTrue if both operands areTrue. E lse, it returns a False.

T he Or operator returns a True if either of its operandsis True, else it returns a False.

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Common Visual Basic Functions

Format Date or number converted to atext string

Now Current time and dateSqr Square root of a numberStr Number converted to a text

stringT ime Current time as a text stringVal Numeric value of a given text

string

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E xercise 3S avings Account

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Visual Basic Branching

Branching statements are used to cause certainactions within a program if a certain conditionis met.

The if statement is used to check a conditionand if the condition is true, we run a block of statements (called the if-block ), else weprocess another block of statements (calledthe else-block ). The else clause is optional.

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If S tatements

The simplest is the If/ Then statement:If Balance - Check < 0 Then

Print "You are overdrawn³Here, if and only if Balance - Check is less thanzero, the statement You are overdrawn isprinted.

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If S tatements

You can also have If/ Then/End If blocks toallow multiple statements:

If Balance - Check < 0T

henPrint "You are overdrawn"Print "Authorities have been notified"

End If In this case, if Balance - Check is less thanzero, two lines of information are printed.

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If S tatementsIf/ Then/Else/End If blocks:If Balance - Check < 0 Then

Print "You are overdrawn"

Print "Authorities have been notified"E lse

Balance = Balance - CheckEnd If

Here, the same two lines are printed if you are overdrawn (Balance -Check < 0),but, if you are not overdrawn ( Else), your new Balance is computed.

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If S tatementsOr, we can add the ElseIf statement:If Balance - Check < 0 Then

Print "You are overdrawn"

Print "Authorities have been notified"E lseIf Balance - Check = 0 Then

Print "Whew! You barely made it"

Balance = 0E lse

Balance = Balance - Check

End If

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S elect Case - Another W ay toBranch

S elect Case format can be used when thereare multiple selection possibilities.

Runs one of several groups of statements,depending on the value of an expression.Select [ Case ] testexpression

[ Case expressionlist [ statements ] ][ Case E lse [ elsestatements ] ]

End Select

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using the If statement:If Age = 5 T henCategory = "Five Year Old"

E lseIf Age > = 13 and Age <= 19 T henCategory = " Teenager"

E lseIf (Age > = 20 and Age <= 35) Or Age = 50 Or (Age > =60 and Age <= 65)

T henCategory = "Special Adult"

E lseIf Age > 65 T henCategory = "Senior Citizen"

E lseCategory = " Everyone E lse"

E nd If

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code with S elect CaseSelect Case AgeCase 5

Category = "Five Year Old"Case 13 To 19

Category = " Teenager"

Case 20 To 35, 50, 60 To 65Category = "Special Adult"

Case Is > 65

Category = "Senior Citizen"Case E lse

Category = " Everyone E lse"E

nd Select

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E xercise 4Password validation

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