14 1414 CHAPTER Programming MIS105 Week-15/ Lec02 Irfan Ahmed Ilyas.

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Programming

MIS105

Week-15/ Lec02

Irfan Ahmed Ilyas

02/3/2002 Prepared By: Irfan Ilyas 2

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Lecture Objectives• Phases in Software Development Cycle

– Phase1: Program Specifications– Phase2: Program Design (Documentation Techniques)

• Psuedo code• Flow charting

– Phase 3: Program Coding– Phase 4: Program Testing– Phase 5: Installing the Program– Phase 6: Program Documentation– Phase 7: Program Maintenance


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3. Program Code• Program design/ flow chart logics are transferred

to Computer Language Code

• Two main types of Computer Languages– Low Level (Machine Languages)

• A computer’s own internal language• Different for every computer• Very complex to write programs• Memory addresses need to be used literally• Example: machine code of Intel x86 processors or

21 4A5E 4096

A Machine Language Instruction


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… 3. Program Code• ….Main types of Computer Languages

– High Level (Symbolic Languages)• Uses English like syntax• Commonly used on different hardware platforms• Much easier to use than machine languages• Simple symbolic names can be used for Memory

addresses• Needs a translator program (compiler) to generate

the equivalent machine code• Examples: Quick BASIC, C++, Java

LET TOTAL = AMT1 + AMT2

A program instruction in Quick Basic


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….2- Example ( Advantage Advertising)C++ Code for “Compute time for Client A”


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…3. Program Code (Issues)• A variety of High Level Languages are available,

including• Visual Basic,• Visual C• Java• Small Talk• Fortran

• Selecting a particular language depends upon– The expertise of the programmer– Resources available for the program (hard-disk space, monitor

type etc.)– The application area of the program


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4. Program Test (Debugging)

• Process of removing bugs (errors) from a program• Possible error types

– Syntax Errors (Coding Errors)• Coding incorrectly

• Causes: Typing mistakes/ violating language rules

• Example:– PRNT “Hello” ‘A syntax error in PRINT statement of Quick

Basic

– printf(“%s: %d”,”Result”,x) ‘In C++, statement does not end with a semicolon (;)


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…4. Program Test (Debugging)

• ….Possible error types– Logic Errors (Algorithm Errors)

• Mistakes in algorithm steps

• Results in – incorrect outputs

– Run-time crashes

• Causes:– Mistakes in the instruction sequence

– Using inappropriate instructions

• Not very obvious when happening with some particular values of data inputs


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…4. Program Test (Debugging)• How to debug?

– Syntax Errors• Carefully comparing the program with the language valid codes• Captured automatically by the translator programs (compilers)

– Logic Errors• Running the program with test data (input values for

which correct results are known)• Logic errors are pinpointed when

– a known input-output pair doesn’t match– Program crashes for some input values.

• Debugger Programs are available (with almost all language compilers) to pinpoint logic errors


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…4. Program Test (Debugging)

• Standard program testing procedure– Desk checking– Manual testing with sample (test) data– Attempt at translation– Testing sample data on computer– Testing by a selected group of potential users

(beta users)


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5. Installing the Program

• A program is usually implemented as part of an overall, integrated information system

• Example:– An Accounting Information System

• Composed of many different programs (built independently)

• Each program works for a different accounting area like general ledger, payroll etc.

• The programs are then implemented in an integrated manner to bring up the overall information system


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6.Program Documentation

• Documentation explains every facet of a program (usage, development, error-handling)

• Should be on-going throughout program development

• Should be compiled and organized at the final stages

• Addresses three possible communities– Program Users– Program Operators– Program Developers


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7. Program Maintenance

• Two broad Maintenance categories– Correction of emerging errors– Modification for changing user needs

• Significantly consumes the share of total development time (>75%)

• Mostly done by specially hired programmers (Maintenance Programmers)


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Lecture Objectives

• Introducing Object Oriented Programming (OOP)– Classes & Objects– Attributes & methods

• Benefits of OOP– Reusability (inheritance)– Hiding complexity (encapsulation)– Context driven functionality (polymorphism)


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… Lecture Objectives

• Introducing Microsoft Access VBA Programming– Concept of Microsoft Access application– VBA- Object based Programming – Microsoft Access Objects– Event driven programs– Event procedures


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Object Oriented Programming (OOP)

• Object is a programming unit having – data (attributes)– methods (operations)

• Every object represents some physical object in the real life situation (being programmed)

• Every object in a program is created from its Class.• Programmers write Class code for every needed object (class)

• Main program is just creating objects and make use of their functionalities


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Example: Advantage Advertising

Client_BillClientNameRegularHoursOvertimeHoursRegularRateOvertimeRate

computeClientBill( TimeCardRecords )printBill( )

Client_Bill object for Client A

Main Program

Client_Bill object for Client B

A class for client bill object

Attributes

Methods


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Example: Advantage AdvertisingPsuedo code for the main program (using Client_Bill Objects)

START PROGRAM Create object bill_for_clientA from class Client_Bill

bill_for_clientA = new Client_Bill() Setting client attributes

bill_for_clientA.clientName= “ClientA”bill_for_clientA.RegularRates=100……

Calling object method for computing the billbill_for_clientA.computeClientBill ( timecardRecords )

Calling object method for printing the billbill_for_clientA.printClientBill ()

END PROGRAM


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Benefits of OOP

• Maximize Code Reusability– Pre-written class codes can be used in any program development– New classes can be derived from pre-written classes with some

added functionalities [Inheritance]– Example: Car class can be used for deriving more specific car

classes Toyota, Lexus, Mercedes etc.

• Simplify Program Writing– Users of an object do not need to know the exact mechanism of

any of the object functionalities [Encapsulation]– Easier for the programmers to change the functionality mechanism

any time without asking users to change their programs


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…Benefits of OOP

• Context driven method calls– Some methods look similar in interface and semantics

but implemented differently for different objects [Polymorphism]

– User doesn’t need to worry about the mechanism – Example:

• print method in Client_Bill class• For two different types of client bills

(clilent_printed_bill & client_onscreen_bill), the methods print does the same (semantically), however using different mechanism


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Introducing Visual Basic for Applications

• Visual Basic for Applications (VBA) is the language for building applications with Microsoft office products

• VBA is an Object Based Language (not fully object Oriented)– It doesn’t allow you to use inheritance & polymorphism features– Encapsulation feature can be used to some extent.

• VBA allows to program already existing objects in different Microsoft Applications


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…Introducing Visual Basic for Applications

• VBA code helps in integrating the use of different objects (tables, queries, forms etc.)

• Produces the effect of a completely customized application


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An Example Microsoft Access Database

Tables-tblStudent-tblCourse-tblGrades

QueriesForms

-frmStudentManagement-frmCourseManagement-frmStudentGrades

A Microsoft Access Database (college.mdb)

User needs to use database objects interactively (using the command interface available in Access)


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An Example Microsoft Access Application

College.mdb Database Objects

Users use all objects in an integrated fashion


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VBA in Microsoft Access Environment

• Microsoft Access provides an event driven programming environment

• An event is a specific action that occurs on (or with) a certain Access object.

• Every object in Microsoft Access has a series of events defined.– Command Button Events

• Click, DblClick, GotFocus, LostFocus, MouseMove, MouseDown, MouseUp

– Form Events• Load, LostFocus, MouseDown, MouseUp, OnConnect, OnDiscount etc.

– And many others


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Event Driven Programming

• An event may come into action (initiated/ triggered) because of– a user action (clicking, pressing a key, changing data etc.)– A time value reached (timing events)– A consequence of another event

• Programmers are allowed to write a series of actions (VBA code/ Macro commands) in response to any event.

Event Name Objects allowing the eventmouse click

command buttoncheck boxForm (Header/ Footer/ Detail Sections)radio button

changes in datatext boxcombo boxlist box

Opening or closingForm

Examples of Events in Microsoft Access

Event Name Objects allowing the eventmouse click

command buttoncheck boxForm (Header/ Footer/ Detail Sections)radio button

changes in datatext boxcombo boxlist box

Opening or closingForm

Examples of Events in Microsoft Access


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An Example Event Driven Program

•Event Chart for a command button object

•Click event has a VBA Procedure attached to it.

Private Sub Command5_Click()MsgBox "Command Button Works OK"End SubMouse Click Event Happens

Go to the event chart of the command button

Run the procedure attached to it.

Program Output


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Main components of VBA Programming

• Writing Procedures– VBA statements are written in form of procedures– A procedure is a series of VBA statements– A procedure may be

• attached to any objects event (event procedure) Or• written separately (without linking it to any object)

– Syntax:Sub procedure_name( ) statement 1 statement 2 : :End Sub


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….Main components of VBA Programming

• What to write in VBA Procedures?– Data declaration statements

• Syntax: – Dim variable_name As data_type_in_VBA

• Example:– Dim X As Integer

– Calling Microsoft Access standard Procedures\ Functions (e.g. MsgBox)

• Syntax: – MsgBox(prompt[, buttons] [, title] [, helpfile, context])

• Example: – MsgBox(“My First VBA Program”, vbOK, “Test Message”)


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• .. What to write in VBA Procedures?– Using Microsoft Access objects

• Setting attributes/ calling methods from Microsoft Access Objects

• Syntax:– ObjectName.attribute_name = <new value>– ObjectName.method_name [arguments]

• Example:– DoCmd.OpenForm frmStudents

– Forms!frmStudents.Caption = “New Caption”

– Me.Caption = “Changed Caption”


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• .. What to write in VBA Procedures?– Using VBA Control Structures

• Selection StructureIf condition Then

Statement(s)[Else

Statement(s)]End If

• Example:If value = 0 Then

AlertLabel.ForeColor = "Red"

AlertLabel.Font.Bold = True

AlertLabel.Font.Italic = True

End If


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• .. What to write in VBA Procedures?– Using VBA Control Structures

• Loop Structure

• Example:


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Generations of Programming Languages

• Occurring in “generations”– Levels

– Machine languages to natural languages

• Lower level closer to machine language

• Higher level closer to human-like language


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Generations of Languages• 1st -- Machine languages

• 2nd -- Assembly languages

• 3rd -- High level procedural languages

• 4th -- Problem-Oriented Languages

• 5th -- Natural Languages & Visual

programming


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14 1414 CHAPTER Programming MIS105 Week-15/ Lec02 Irfan Ahmed Ilyas.

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