Algorithms_and_Flowcharting.pdf

7/27/2019 Algorithms_and_Flowcharting.pdf

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AlgorithmandFlowcharting


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LessonObjectives

Attheendofthelecturethestudentsshouldbe

ableto:

Definetermsinprogrammingsuchas:system,SDLC,

flowcharting,algorithm,compile,syntaxerrors,etc.

Knowthestepsinprogramming.

Knowthedifferentsymbolsforflowchartingandhow

touse

them.


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Whatissystem?

Isanorganizedsetofrelatedcomponents

establishedto

accomplish

acertain

task.

Note:Therearenaturalsystemssuchasthe

bodys

cardiovascular

system

but

many

systems

havebeenplannedanddeliberatelyputintoplace

bypeople.


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Whatissystem?

Forexample:afastfoodfranchisehasasystemof

servingacustomer

including

taking

an

order,

assemblingthefoodandcollectingtheamount

due.


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Phases of SDLC

System Development Life CyclePreliminary Investigation: Determining the

problem

Analysis: Understanding the existing systemDesign: Planning the new system

Development: Doing the work to bring the newsystem into being

Implementation: Converting the new system


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SDLC

Analysis-gather data-analyze data

-develop requirements

Implementation-training

-conversion-evaluation

-maintenance

Preliminary Investigation-problem definition

Design-preliminary design

-detail design

Development-scheduling

-programming-testing


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ComputerProgram

Isasetofdetailed,stepbystepinstructionsthatdirects

the

computer

what

you

want

it

to

do.

It

is

a

notation

for

expressinginstructionstobecarriedoutbyacomputer.

Programsarewritteninaprogramminglanguage,which

isaset

of

rules

that

provides

away

of

telling

the

computerwhatoperationstoperform.

Thepersonwhocreatescomputerprogramiscalled

computerprogrammer.


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Activities Involve in

Programming

Understand the problem.

Plan the logic.

Code the program.

Compile the program into machine

language.

Test the program.

Put the program into production.


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Activities involve in

Programming

Understanding the Problem

Before writing the program the programmer must first

understand the problem.

Satisfy the users need

One of the most difficult task since description of what

is needed may be vague, or worse yet, the user may

not even know what he/she wants.

A good programmer is part counselor, and part

detective.


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Programming

Plan the Logic

The process of planning for the solution of theproblem.

They are referred to as ALGORITHMS

Two most common tools are FLOWCHARTS andPSEUDOCODE.

Involves writing down steps (in English).

The programmer doesnt worry about syntax at this

point, just the sequence of events that will lead from

available input to the desired output.


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Programming

Code the Program

There are over 400 programming languages that

exist.

Most programming languages have translatorsalso known as compiler and interpreters.

Pascal, C, C++, Visual Basic, Cobol, etc.

The part in which the programmer worry about thecorrect syntax; command, punctuation, spelling, etc.

The actual construction of the source code.


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Programming

Compile the program into Machine Language

Machine language - the only language a machine

knows.

Its consists of 0s and 1s.

Compiler is a special program that translates high-level

language instructions into machine language. Compiler catches all syntax errors.


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Programming

Test the Program

To execute and then run the program. The program uponexecution is being subjected to different kinds of test data

to anticipate and correct errors that might occur beforereleasing the program to the users.

Errors can be classified into two: (1) syntactical or logicalerrors (2) compile or run-time errors.


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Programming

Put the Program into Production

The organization can now use the program.

Training personnel to use the program.

Running the program using the actual data.

Test for users approval.


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Algorithm

A sequence of well-understood steps that one takes to

do something. A set of instructions for a person to follow in order to

accomplish a certain task.

A sequence of instructions that tell how to solve aparticular problem.

It is a finite set of instructions that specify a sequence ofoperations to be carried out in order to solve a specificproblem or class of problems.

Examples: directions for going to a certain place

baking a chocolate cake

computing income tax searching for a name in a telephone directory


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Example:

Prepare a Cup of Coffee Step 1: Fill kettle with water.

Step 2: Turn on stove. Step 3: Put kettle on stove.

Step 4: If water is boiling proceed to step#5 otherwise wait.

Step 5: Turn off stove

Step 6: Fill mug with boiled water

Step 7: Put 1 tsp. of coffee in mug.

Step 8: With sugar, put 2 tsp. of sugar in mug, otherwise proceedto step#9.

Step 9: With milk, pour 1 tbsp. of milk in mug, otherwise proceed tostep#10.

Step 10: Stir contents of mug


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Characteristics of an Algorithm

Specify each step or instruction exactly.

There must be no ambiguity.

The instructions must be clear.

There must be a finite number of steps.

The algorithm must terminate.

There must be a stopping point.

There must be an output.

The algorithm must produce the correct result.


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Flowcharting

What is Flowcharting?

A graphical representation of the logical steps that solves a

problem. Programmers use flowcharts to understand the logic

processing of data.

To visualize how statements in a program are interrelated.

Although time consuming, its the best tool for beginners.

Use of symbol and phrases to designate the logic of how aproblem solved.

A common method for defining the logical steps of flow within aprogram by using a series of symbols to identify the basicinput, process and output (IPOs) function within a program.

A diagram representing the logical sequence in which a

combination of steps or operation is to be performed. It is ablueprint of the program.


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Flowcharting

Types of Flowcharts

Program FlowchartsDepicts the detailed logical flow of process in a program.

System Flowcharts

Shows the logic flow of data from one source to another.Divided into functions of departments or personnel.

Symbols are used to represent documents used andoperations undertaken.

Highlights excessive information flow, duplication ofinformation stored in different locations and reasons for

delay of transactions.


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BasicFlowcharting

Symbols

Terminal block

Input/Output block

Process symbol

Decision symbol

On-page Connector

Off-page Connector

Initialization symbol

Flow lines

Flowcharting


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BasicFlowcharting

Symbols

Terminal

Terminal

usedtosignifythebeginningand

endofflowchart

Flowcharting

OVALOVAL

STARTSTART


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BasicFlowcharting

Symbols

Preparation/Initialization

signifiesthepreparationofdata

Used

to

select

initial

conditions Usedtorepresentinstructionsor

groupofinstructionsthatwillalter

or

modify

a

programs

course

of

execution

Flowcharting

HexagonHexagon

SUM=0SUM=0PRODUCT=0PRODUCT=0


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BasicFlowcharting

Symbols

Input/Output

showsinputandoutput.Data

areto

be

read

into

the

computermemoryfroman

inputdeviceordataaretobe

passedfrom

the

memory

to

an

outputdevice.

Flowcharting

ParallelogramParallelogram

Read ARead A

Print APrint A


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BasicFlowcharting

Symbols

Process/Processing

performsanycalculationshat

areto

be

done.

Flowcharting

RectangleRectangle

Sum = A+BSum = A+B


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BasicFlowcharting

Symbols

Decision

signifiesanydecisionsthataretobe

done.Twoalternativeexecution

pathsarepossible. Thepathtobe

followedisselectedduringthe

executionbytestingwhetherornot

thecondition

specified

within

the

outlineisfulfilled.

Flowcharting

DiamondDiamond

If x>5If x>5T F


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BasicFlowcharting

Symbols

OnpageConnector

showtheentryorexitpointoftheflowchart.Anonprocessingsymbolusedtoconnectonepartofaflowchart

to

another

without

drawingflowlines.Conservesspacebykeepingrelatedblocksnearoneanother,reducesthenumberofflowlines

in

complex

program

and

eliminatescrosslinesfromtakingplace.

Flowcharting

AA

Small CircleSmall Circle


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BasicFlowcharting

Symbols

OffpageConnector

designatesentryortoexitfrom

onepage

when

aflowchart

requiresmorethanonepage.

Flowcharting

PentagonPentagon

BB

Fl h ti


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BasicFlowcharting

Symbols

Flowlines

signifiestheprocessthatisto

beexecuted

next

Flowcharting

Fl h ti


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Basic Flowcharting

Almost every program involves the steps of input,

processing and output.

Example:

Get number

Answer = number *2Print Answer

Most flowcharts need some way to separate each step.

Drawing different boxes around each statement is thestandard convention.

Input operation are represented in a parallelogram. A

statement in English is written inside the parallelogram.

Flowcharting

Fl h ti


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Answer = number * 2

Getnumber

Arithmetic statements are

examples of processing

statements, are placed inside

the process box.

Output statements use the

same symbol as that of input

statements - parallelogram.

To show the correct sequenceof events arrow, flow lines and

the terminal symbol (for begin

and end) are used.

begin

Flowcharting


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begin

Get number

Answer= number * 2

Print Answer

end

The next step the programmer

shall do is to find the necessary

language in which to code the

flowchart.

Fl h ti


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What are Variables?

Memory allocations, the content of which may vary/change.

The capability of memory variables to change its content

makes the computers and programming worthwhile.

Because one memory location can be used over and overagain with different values, program instructions can be

written once and then used for thousands of problems.

Giving names (for identification) may vary from oneprogramming language to another; some may allow

hyphens; others allows underscores; some languages allow

dollar signs, others dont. There are languages that limits the

length of names to a variable.

Flowcharting

Fl h ti


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Rules in naming variables...

Must be one word.

May contain letters, numbers, hyphens,

underscores.

Must not start with a number.

Must not contain a space.

Must have some meaning.

Invalid Variable names

interest rate - should be one word

rate! - contains ! an invalid character

xyxxx - although this is allowed, it doesnt mean

or imply anything that it may hold.

#total - should not start with a special character.

Flowcharting

Flowcharting


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Types of Variables Numeric Variables

The type of variable that can hold a number.

In this example: Answer = number * 2 Some languages allow additional types of data; Pascal and C

distinguish between integer or whole number numeric variables and

floating point, decimal and fractional numeric variables.

Character, Text or String Variables

Variables that can hold letters of the alphabet and other special

character such as punctuation marks.

Example:NAME = WASHINGTON

Logical or Boolean Variables

A special type of variable that can only have two values - TRUE or

FALSE.

Flowcharting

Flowcharting


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Arithmetic Operators and Mathematical Statements Addition (+)

Subtraction (-)

Multiplication (*) Division (/)

Modulus (%)

A mathematical statement is composed of a left variable, an

assignment operator (usually in the form of an equal sign) a

series of operands(may be a set of the same variables or a new

set of variables, and /or constants) and (arithmetic) operators.

Example:

x = x + 1

sum = a + b

Flowcharting

Flowcharting


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Constants

A constant is a value that never changes during the

execution of the program. Constants can be any type-numeric, alphabetic or

special symbols.

Like variable, constants can be named. The computersets up a specific memory location to hold the value of

the constant.

During the execution of the program, the constant isreferred to by name. Once the constant is given a

value, it cannot be changed during the execution of

the program.

Flowcharting

Flowcharting


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Relational Operator A relational operator compares two values and

determines the relationship between them.

Operator Use Returns true if

> op1 > op2 op1 is greater than op2

>= op1 >= op2 op1 is greater than or equal to op2

< op1 < op2 op1 is less than op2


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Logical Operators

Use logical operators (also called Boolean operators) to

express relationships between search expressions.

Operator Use Returns true if

and cond1 and cond2 both condition should be true

or cond1 or cond2 either one of the condition is true

not (negation) not cond

! cond

Flowcharting

ADVANTAGES OF USING


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ADVANTAGES OF USING

FLOWCHARTS

1. Communication: Flowcharts are better way of communicating the logic

of a system to all concerned.

2. Effective analysis: With the help of flowchart, problem can be analyzed

in more effective way.

3. Proper documentation: Program flowcharts serve as a good programdocumentation, which is needed for various purposes.

4. Efficient Coding: The flowcharts act as a guide or blueprint during the

systems analysis and program development phase.

5. Proper Debugging: The flowchart helps in debugging process.

6. Efficient Program Maintenance: The maintenance of operating program

becomes easy with the help of flowchart. It helps the programmer to put

efforts more efficiently on that part

LIMITATIONS OF USING


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LIMITATIONS OF USING

FLOWCHARTS

1. Complex logic: Sometimes, the program logic is quitecomplicated. In that case, flowchart becomes complex andclumsy.

2. Alterations and Modifications: If alterations are requiredthe flowchart may require re-drawing completely.

3. Reproduction:As the flowchart symbols cannot be typed,

reproduction of flowchart becomes a problem.

4. The essentials of what is done can easily be lost in the

technical details of how it is done.

L i St t


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Simple Sequence

Logic involves executing instructions one

statement after another-in the order presented by

the program.

This is the simplest and most-used pattern.

The computer assumes that all instructions are

to be executed in this order unless the programpresents other instructions.

Logic Structures

Logic Str ct res


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A simple sequence pattern

The process is done onestep at a time

Logic Structures

Logic Structures


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Selection Structure

Requires that the computer make a choice among

two or more items.

Each choice is based on one of three comparisons acomputer can make: equal to, less than or greater

than.

Logic Structures

Logic Structures


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Selection pattern

A decision is

made orchoosingbetween a set of

options

Logic Structures

Logic Structures


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Iteration Structure

causes an interruption in the normal sequence of

processing and directs that computer to loop back toa previous statement in the program, repeating the

same sequence over again, usually with new data.

By looping the programmer avoids having to repeatthe same set of instructions over and over.

Logic Structures

Logic Structures


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Iteration pattern

A set of repeated

statements areexecuted until thedesired output is

acquired.

Logic Structures

Logic Structures


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Linking pattern

An on-pageconnector is used to

redirect the flow ofthe chart.

Logic Structures

Logic Structures


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Iteration structureexample...

Example 1

Draw a flowchart to find the

sum of first 50 natural

numbers.

Logic Structures

Logic Structures


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Example 2Draw a flowchart

to find the

largest of three

numbers A,B,and C.

Selection structure

example...

Logic Structures


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The CASE structure

Drawaflowchartthatwillacceptanddisplayanumber. WriteiDrawaflowchartthatwillacceptanddisplayanumber. Writeitsequivalenttsequivalent

algorithmsalgorithms


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algorithms.algorithms.

Algorithm:

Step1:ReadinthevalueofN.

Step2:PrintthevalueofN.

START

READ N

PRINT N

END


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FlowchartSamples

DrawaflowchartthatwillcomputeanddisplaythesumandproduDrawaflowchartthatwillcomputeanddisplaythesumandproductoftwoctoftwo


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numbers. Writeitsequivalentalgorithm.numbers. Writeitsequivalentalgorithm.

Algorithm:

Step1:

Initialize

Sum

and

Product

into

0.

Step2:ReadinthevaluesofAandB.

Step3:ComputethesumbyaddingAandBthencomputetheproductby

multiplyingA

and

B.

Step4:PrintthecomputedvalueofSumandProduct.

START

Read A,B

Print Sum,

ProductEND

Sum = 0Product = 0

Sum = A + B

Product = A * B

ConstructaflowchartthatwillconvertaninputtednumberinFaConstructaflowchartthatwillconvertaninputtednumberinFahrenheittoitsequivalenthrenheittoitsequivalent

measure in Celsiusmeasure in Celsius


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measureinCelsius.measureinCelsius.

Formula:C=(5/9)*(FFormula:C=(5/9)*(F32)32)

Algorithm:

Step1:

Initialize

Celsius

into

0.

Step2:ReadinthevalueofFahrenheit.

Step3:ComputethevalueofCelsius.

Step4:

Print

the

computed

value

of

Celsius.

START

Read Fah

Print

CelsiusEND

Celsius=0

Celsius=(5/9)*(Fah-32)

DrawaflowchartthatwillinputvaluesforAandB. ComparetwDrawaflowchartthatwillinputvaluesforAandB. Comparetwovaluesinputtedandprintovaluesinputtedandprint

h h f h l h h l d h k h l l h


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whichofthevaluesishigherincludingtheremarkwhichofthevaluesishigherincludingtheremarkHigherHigher. Writeitsequivalentalgorithm.. Writeitsequivalentalgorithm.

Algorithm:

Step1:ReadthevaluesofAandB.

Step2:TestifAisgreaterthanB.

Step3:IfAisgreaterthanB,Aishigher. However,ifAislessthanB,Bishigher.

Step4:PrintthenumberandtheremarkHigher

START

Input A,B

Print A,

Higher

END

A > B

Print B,Higher

T

F

DrawaflowchartthatwillinputgradeofstudentanddetermineDrawaflowchartthatwillinputgradeofstudentanddeterminewhetherthegradeispassedorwhetherthegradeispassedor

f il d P i h d d k f d W i if il d P i h d d k f d W i i i l l i hi l l i h


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failed. Printthename,gradeandremarksofstudent. Writeitfailed. Printthename,gradeandremarksofstudent. Writeitsequivalentalgorithm.sequivalentalgorithm.

Algorithm:

Step1:Initializenameandremarksintoblanks.

Step2:ReadinvaluesforGradeandName.

Step3:

Test

if

Grade

is

greater

than

or

equal

to

60.

Step4:IfGradeisgreaterthanorequalto60,remarkisPassed. However,ifGradeisbelow60,remarkisFailed

Step5:Printthename,gradeandremarks.

START

Read Name,Grade

END

If Grade>60

Print Name,Grade, Remarks

Name= Remarks =

Remarks =Failed

Remarks =Passed

SEATWORKSEATWORK


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SEATWORKSEATWORK

DEIManufacturingCompanyplanstogiveayearDEIManufacturingCompanyplanstogiveayearendbonusendbonus

toeachofitsemployee. Drawaflowchartwhichwilltoeachofitsemployee. Drawaflowchartwhichwillcomputethebonusofanemployee. Considerthefollowingcomputethebonusofanemployee. Considerthefollowing

conditions:Iftheemployeeconditions:Iftheemployeesmonthlysalaryislessthan2,000smonthlysalaryislessthan2,000

pesos,the

bonus

is

50%

of

the

salary;

for

employees

with

pesos,

the

bonus

is

50%

of

the

salary;

for

employees

with

salariesgreaterthan2,000pesos,thebonusis1,500pesos.salariesgreaterthan2,000pesos,thebonusis1,500pesos.

PrintthenameandthecorrespondingbonusforeachPrintthenameandthecorrespondingbonusforeach

employee.Write

each

equivalent

algorithms.employee.

Write

each

equivalent

algorithms.

Pseudocode


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Pseudocode

uses everyday language to prepare a brief set of instructions

in the order in which they will appear in the finished program. It is an abbreviated version of actual computer code (that's

why it is called pseudocode).

Pseudocode looks more like a real program than the flowchartdoes. It allows the programmer to focus on the steps required

to solve a program rather than on how to use the computer

language. An advantage of pseudocode is that it can be used to

describe a program to a nontechnical user and can still

provide guidelines for the writing of program code.

Pseudocode


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Pseudocode

A textual presentation of a flowchart

Close to a natural language

The control structures impose the logic May become a part of the program documentation

Could be translated into a program

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