02 algorithm, pseudocode and coding

8/10/2019 02 Algorithm, Pseudocode and Coding

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COMPUTER AND PROGRAMMINGPSEUDOCODEFLOWCHART

Algorithm and Programmingsession 2


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The Computer


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Physical Description of a

Computer

Main components of a Computer

A computer is a digital electronic machine composed of three main components:Central Processing Unit (CPU), memory, and input/output peripherals.

The processor carries out instructions which are stored in the memory. Along with theinstructions, data is also stored in memory.

The processor typically is instructed to manipulate the data in some desired fashion.

Input/output devices take information from agents external to the machine and provideinformation to those agents.

Input devices are typically keyboards, disk drives and tape drives.

Output devices are typically monitors, printers, disk drives and tape drives.

The computers used in this course are connected in a UNIX system to allow shared

use of resources and devices


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Programs

Computers are very general purpose machines. They can be used toperform a great variety of different tasks:- writing documents, solvingnumerical and mathematical problems, drawing pictures, sending "e-mail" messages to friends etc. However, in order for the computer toperform all these tasks the computer needs to be provided with detailed

instructions as to how it is to go about the job. A program is a set of instructions which specifies how a computer is to

perform a particular task. Programs may be very complex. For examplea spreadsheet program can display large amounts of information andperform complex calculations. Whereas a simple program might do

nothing more than check the clock and print the current date and time onthe screen.

All computers come with a large number of programs pre-installed andyou can buy new programs for many different tasks.


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Programming

As a programmer you can create new programs and add them to theexisting suite of programs so that your computer can tackle new tasks.Your computer will provide a variety of existing programs which allowyou to create, test and modify your own programs and eventually, whenyour program is working correctly to install it for your own use. In this

course, you will become familiar with some of these program buildingprograms or "programming tools". Programs are always written using aprogramming language, of which C++ are examples.

Computers follow the instructions in programs literally so if you make amistake in the program the computer will do what it is told (not what you

intended). This is usually easy to spot in small programs but largeprograms need to be designed and written very carefully to make surethat they work correctly.

Learning to program requires not just learning a new language but alsolearning how to use it effectively.


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Programming is a core activity in the process ofperforming tasks or solving problems with the aid of acomputer. An idealised picture is:

[problem or task specification] - COMPUTER- [solution orcompleted task]
http://www.doc.ic.ac.uk/~wjk/C++Intro/computer.htmlhttp://www.doc.ic.ac.uk/~wjk/C++Intro/computer.html


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The Origins of C++

C++ was developed by Bjarne Stroustrup ofAT&T Bell Laboratories in the early 1980's, and isbased on the C language. The name is a pun -

"++ means C++ is intended as an incrementalimprovement of C. Most of C is a subset of C++,so that most C programs can be compiled (i.e.converted into a series of low-level instructions

that the computer can execute directly) using aC++ compiler.


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ANSI C++

The American National Standards Institution (ANSI) provides "official"and generally accepted standard definitions of many programminglanguages, including C and C++. Such standards are important. Aprogram written only in ANSI C++ is guaranteed to run on any computerwhose supporting software conforms to the ANSI standard. In otherwords, the standard guarantees that ANSI C++ programs are portable. Inpractice most versions of C++ include ANSI C++ as a core language, butalso include extra machine-dependent features to allow smoothinteraction with different computers' operating systems. These machinedependent features should be used sparingly. Moreover, when parts of a

C++ program use non-ANSI components of the language, these shouldbe clearly marked, and as far a possible separated from the rest of theprogram, so as to make modification of the program for differentmachines and operating systems as easy as possible.


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Stages of Programming


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Creating

Creating a program involves two main stages: designing a program to achieve the required goals, and physically creating the program.

Throughout the course we will look at how to design programs and the techniques that canbe used. We will first lookat how the physical program is created once the design stagehas been completed. To create a physical program it has to be entered into the

computer. To do this, normally a file is opened and the text of the program is typed in.When programming in C++ the name of the file by convention ends with .cpp (full stop,lower case cpp) or .C or .cxx, e.g.

Example filenames using .cpp - program.cpp, hello.cpp or myfile.cpp Example filenames using .C - program.C, hello.C or myfile.C Example filenames using .cxx - program.cxx, hello.cxx or myfile.cxx

The part of the filename after the . (dot) is known as the file extension. In general eachprogramming language has a different convention for the file extension. The program isnormally entered using a standard text editor such as nedit, vi or emacs. Having enteredthe program, the contents of the file are saved and you would exit from the text editor.The information held in this file is known as the sou rce code.


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Compiling

To Compile and link the source code, useunder Linux GNU compiler, and type as theexample :

g++ hello.cpp o hello(Enter the correct name of the file in which you entered your program in the creationstep). If there are errors in the program, such as omitting the semi-colon after the coutstatement, the compiler will detect the errors and report them. If errors are indicated theymust be corrected by re-editing the program in the file. The compiler can then be

invoked again, using the above command, until no errors are reported. As well asindicating errors which will be flagged with the word Error, the compiler may alsoproduce Warnings. These are not errors which must be corrected before the programcan run, but are instead indications from the compiler that it thinks your program orsyntax are suspicious. They do not need to be corrected, but you should alwaysinvestigate how significant they are. Once the compiler has successfully compiled theprogram an executable file named a.out will exist.


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Running

To run the program you just type./hello

at prompt (hello is the filename)


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The Steps of Creating Program

1.Type the command in text editor

2.Save the file with .cpp extension

3.Go to terminal4.Go to the same directory with the .cpp file

you've typed (by type cd dirname)

5.Type g++ filename.cpp -o filenameto compilethe file

6.To run the program, type ./filename


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Exercise


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#include int main(int argc, char *argv[])

{QCoreApplication a(argc, argv);

return a.exec();

} 09/23/07


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Please try to write thiscommand// Program written September 2014

// by My Group

#include

using namespace std;main()

{

cout


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program

// program to add two integer values and display result

#include

#include

using namespace std;

int main(int argc, char *argv[])

{

QCoreApplication a(argc, argv);

//declare variablesint value1, value2, sum;

// assign values and compute the result

value1 = 32;

value2 = 27;

sum = value1 + value2;

// display the result

cout


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#include


int Tambah(int x,int y){

cout


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Building A Program


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Introduction to Design and Style

Before writing a program:

Have a thorough understanding of problemrequirements

Carefully plan your approach for solving it While writing a program:

Know what building blocks are available

Use good programming principlestop-downdesign


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Algorithms

All computing problems can be solved by executing a series of actions in

a specific order

steps should be independent of computer

languageAlgorithmA procedure determining theActions to be executed

Order in which these actions are to be executed

Program control Specifies the order in which statements are to

executed


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Algorithm Development

1) TotalDistance = EndingPointStartPoint

2) ElapsedTime = EndHour + (EndMinute / 60)

+ (EndSecond / 3600)3) Speed = TotalDistance / ElapsedTime


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// Fred Annexstein

// January 2003

// Program to Compute velocity of race car

// Design inserted here

#include


int main() {

cout StartPoint;

cout > EndPoint;

cout > EndHour >> EndMinute >> EndSecond;


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int TotalDistance;

TotalDistance = EndPoint - StartPoint;

float ElapsedTime;

ElapsedTime = EndHour + (EndMinute / 60.0)

+ (EndSecond / 3600.0);

float Speed = Distance / ElapsedTime;cout


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Building a Program

Whatever type of problem needs to be solved, acareful thought out plan of attack, called analgorithm, is needed before a computer solution

can be determined.

1) Developing the algorithm.

2) Writing the program.

3) Documenting the program.

4) Testing and debugging the program.


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Building a Program

1) Developing the algorithm.

Algorithm: A detailed description of the exactmethods used for solving a particular problem.

To develop the algorithm, the programmer needsto ask:

What data has to be fed into the computer?

What information do I want to get out of the computer?

Logic: Planning the processing of the program. Itcontains the instructions that cause the input data tobe turned into the desired output data.


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Building a Program

A step-by-step program plan is createdduring the planning stage.

The two major notations for planning

detailed algorithms:Pseudocode: A verbal shorthand method that

closely resembles a programming language,but does not have to follow a rigid syntaxstructure.

Flowchart: Series of visual symbolsrepresenting the logical flow of a program.


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Building a Program

Start

Count Money

Do youhave more than

$10.00?Go out

Go home

End

No

Yes

1. If money < $10.00 then go homeElse Go out

2. Count money

3. Go to number 1

Pseudocode:Flow chart:


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Building a Program

2) Writing the Program

If analysis and planning have been thoroughlydone, translating the plan into a programming

language should be a quick and easy task.

3) Documenting the Program

During both the algorithm development and

program writing stages, explanations calleddocumentation are added to the code.


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Building a Program

4) Testing and Debugging the Program. The program must be free of syntax errors.

The program must be free of logic errors.

The program must be reliable. (produces correct results)

The program must berobust. (able to detect execution

errors)

User Acceptance testing

Alpha testing: Testing within the company. Beta testing: Testing under a wider set of conditions using

sophisticated users from outside the company.


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Types of Programming Errors

Syntax errorsErrors caught by compiler

Logic errorsErrors which have their effect at

execution timeNon-fatal logic errors

program runs, but has incorrect outputFatal logic errors

program exits prematurely


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Pseudocode


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Pseudo Code

Pseudo means pretend or false

Pseudo Code is pretend or false computer code;generic English-like terms that are somewhat

like computer code Pseudo Code is not as standardized as

flowcharts, and does not facilitate the breakingdown of problems as well as a flowchart does


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Pseudocode

PseudocodeArtificial, informal language used to develop

algorithms

Similar to everyday EnglishNot actually executed on computers

Allows us to think out a program before

writing the code for itUsually easy to convert into a corresponding

C++ program

Consists only of executable statements

P d d f l


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Pseudocode for a sampleproblem

Programming problem: write a program todetermine the speed or velocity of a race car.

What are the inputs?

What are the outputs?

What is the algorithm or process used?

P d d f l


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Pseudocode for a sampleproblem

What are the inputs?Starting point,Ending point,Elapsed time in Hours, Minutes, Seconds

What are the outputs?Speed of Car

What does algorithm compute? Total Distance traveled (in miles) Total Elapsed time (in hours) Speed (in miles per hour)


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Flowchart


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Flowcharts

A Flowchart is a VisualRepresentation of an algorithm

A Flowchart uses easy-to-understandsymbols to represent actions on dataand the flow of data

Flowcharts aid in breaking down aproblem into simple steps


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Basic Flowchart Symbols

ProcessTerminator

Input/Output

Decision

Connector

Data Flow

IndicatesThe beginningof Repetition

Indicatesthe Beginning of

Sub Program


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The Basic Flowchart Symbols

The terminator shows where aspecific piece of an algorithmbeings and ends

A process is a basic action oractions on data

A decision is a logical test withtwo possible data pathsresulting from one

Terminator

Process

Decision


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The Basic Flowchart Symbols

Input/Output gets data ordisplays information to the userof the algorithm

A connector connects two ormore data flows into one

A data flow shows the direction

of datas movement throughthe algorithm

Input/Output

Connector

Data Flow


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Programing Construct

The Three Computer Programming


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The Three Computer ProgrammingConstructs

Any problem, regardless of howcomplex, can be broken down into

three basic CONSTRUCTS

SEQUENCE

SELECTIONITERATION


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Sequence

Sequence is the most basic of theconstructs

It is simply performing one step after

another Each step is followed in a specific

sequence, hence the name

Sequence can be thought of as dothis, then do this, then do this

S


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Sequences

A sequence of instructionsthat are executed in theprecise orderthey are written in:

statement block 1

statement block 2

statement block 3

statement block 1

statement block 2

statement block 3


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Selection / Conditionals

Selection is the decision-makingconstruct

It is used to make yes/no ortrue/false decisions logically

Selection can be thought of as if

something is true take this action,otherwise take that action


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Selection / Conditionals

Select between alternate courses of actiondepending upon the evaluation of a condition

If ( condition = true )

statement block 1

Else

statement block 2

End ifstatement

block 1

conditionTrue False

statementblock 2


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Iteration

Iteration comes from the word reiterate,which means to repeat

Iteration is a looping construct Iteration is a combination of decision and

sequence and can repeat steps

Iteration can be thought of as whilesomething is true, do this, otherwise stop


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Visualizing The Constructs

By using Flowchart symbols, wecan visualize the three basic

computer constructsEvery algorithm ever created is

made up of only these three

constructs


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Exercise of Building Program


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Exercise 1

Write an algorithm to determine astudents final grade and indicatewhether it is passing or failing. Thefinal grade is calculated as the averageof four marks.

passing grade is >=50


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Solution of Exercise 1

Detailed AlgorithmStep 1: Input M1,M2,M3,M4

Step 2: GRADE (M1+M2+M3+M4)/4

Step 3: if (GRADE < 50) thenPrint FAIL

else

Print PASS

endif


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PRINTPASS

Step 1: Input M1,M2,M3,M4Step 2: GRADE (M1+M2+M3+M4)/4Step 3: if (GRADE


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Algorithm

Step 1: Input Lft

Step 2: Lcm Lft x 30

Step 3: Print Lcm

START

Input

Lft

LcmLft x 30

Print

Lcm

STOP

Flowchart

Print Lcm


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Exercise 3

Write an algorithm and draw a

flowchart that will read the two

sides of a rectangle andcalculate its area.


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Pseudocode

Input the width (W) and Length (L) of arectangle

Calculate the area (A) by multiplying L with W Print A


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Algorithm

Step 1: Input W,L

Step 2: A L x W Step 3: Print A

START

InputW, L

AL x W

PrintA

STOP

Print A

E i 4


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Exercise 4

Write an algorithm and draw a flowchartthat will calculate the roots of a quadratic

equation

Hint: d= sqrt ( ), and the roots

are: x1= (b+ d)/2a and x2= (bd)/2a

2ax bx c

24b ac


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Pseudocode: Input the coefficients (a, b, c) of the quadratic

equation

Calculate d Calculate x1

Calculate x2

Print x1 and x2


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Algorithm: Step 1: Input a, b, c

Step 2: dsqrt ( )

Step 3: x1 (b+ d) / (2 x a)

Step 4: x2 (bd) / (2 x a)

Step 5: Printx1,x2

START

Inputa, b, c

dsqrt(b x b4 x a xc)

Printx1,x2

STOP

x1(b+ d) / (2 x a)

X2(bd) / (2 x a)

4b b a

Print x1, x2


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Control Structure

C t l St t


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Control Structures

Sequential execution Statements executed one after the other in the order

written

Transfer of control

When the next statement executed is not the next onein sequence

Only 3 basic control structures Sequence structure Built into C++. Programs executed sequentially by default.

Selection structures C++ has three types - if, if/else, and switch

Repetition structures C++ has three types -while, do/while, and for

C t l St t


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Control Structures

Pseudocode, actual C++ code and Flowchart Graphical representation of an algorithm Rectangle symbol (action symbol)

Indicates any type of action. Oval symbol indicates beginning or end of a program, or a section of

code (circles).

single-entry/single-exit control structures

Connect exit point of one control structure to entrypoint of the next (control-structure stacking). Makes programs easy to build.

Th if S l ti St t


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The if Selection Structure

Selection structure used to choose among alternative courses of action

Pseudocode example:If students grade is greater than or equal to 60

Print Passed If the condition is true print statement executed and program goes on to next

statement

If the condition is false print statement is ignored and the program goes onto the

next statement

Indenting makes programs easier to read C++ ignores whitespace characters

Th if S l ti St t


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The if Selection Structure

Translation of pseudocode statement into C++:if ( grade >= 60 )cout = 60 print Passed

A decision can bemade on any

expression.zero - falsenonzero - trueExample:3 - 4istrue

Th i / S l ti St t


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The if/elseSelection Structure

if Only performs an action if the condition is true

if/else

A different action is performed when condition is true andwhen condition is false

Pseudocodeif students grade is greater than or equal to 60

print Passed

else

print Failed

C++ codeif ( grade >= 60 )

cout


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P bl


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Problem (solve the problem !)

The evaluation criteria are : Student with grade >= 60 is passed, the others

are failed

Students grade with score >=90 is A Students grade with score >=80 is B

Students grade with score >=70 is C

Students grade with score >=60 is D

Students grade with score


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The if/elseSelection Structure

Nested if/elsestructures Test for multiple cases by placing if/elseselection structures insideif/elseselection structures.

if students grade is greater than or equal to 90Print A

else

if students grade is greater than or equal to 80Print Belse

if students grade is greater than or equal to 70Print C

elseif students grade is greater than or equal to 60

Print Delse

Print F

Once a condition is met, the rest of the statements are skipped

DECISION STRUCTURES


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DECISION STRUCTURES

The expression A>B is a logical expression it describes acondi t ion we want to test

i f A>B is true (i f A is g reater than B) we takethe action on left

print the value of A

i f A>B is false (i f A is not greater than B) wetake the action on right

print the value of B

DECISION STRUCTURES


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DECISION STRUCTURES

isA>B

Print

B

Print

A

Y N

Print A Print B

IF THEN ELSE STRUCTURE


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IFTHENELSE STRUCTURE

The structure is as follows

If cond i t ion then

true alternative

else

false alternative

endif

IF THEN ELSE STRUCTURE


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IFTHENELSE STRUCTURE

The algorithm for the flowchart is as follows:If A>B then

pr in t A

elsepr in t B

endif

isA>B

Print

B

Print

A

Y N

Print A Print B

Relational Operators


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Operator Description

> Greater than

< Less than

= Equal to

Greater than or equal to

Less than or equal to

Not equal to


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Exercise


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ALGORITHMStep 1: InputVALUE1, VALUE2Step 2: if (VALUE1 > VALUE2) then

MAX VALUE1

else MAX VALUE2endif

Step 3: Print The largest value is, MAX



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MAXVALUE1

PrintThe largest value is,

MAX

STOP

Y N

START

InputVALUE1,VALUE2

MAXVALUE2

isVALUE1>VALUE2

PrintThe Largest Value is ,

MAX

NESTED IFS


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NESTED IFS

One of the alternatives within an IFTHENELSE statement

may involve furtherIFTHENELSE statement

Exercise 2


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Exercise 2

Write an algorithm that reads threenumbersand prints the value of the largest number.


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Step 1: Input N1, N2, N3Step 2: i f (N1>N2) then

if (N1>N3) thenMAX N1 [N1>N2, N1>N3]

elseMAX N3 [N3>N1>N2]

endif

else

if (N2>N3) thenMAX N2 [N2>N1, N2>N3]

else

MAXN3 [N3>N2>N1]endif

endif

Step 3: Print The largest number is, MAX

Exercise 3


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Exercise 3

Flowchart: Draw the flowchart of the aboveAlgorithm.

Exercise 4


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Exercise 4

Write and algorithm and draw a flowchart to

a) read an employee name (NAME), overtimehours worked (OVERTIME), hours absent

(ABSENT) andb) determine the bonus payment (PAYMENT).

Exercise 4


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Exercise 4

Bonus Schedule

OVERTIME(2/3)*ABSENT Bonus Paid

>40 hours>30 but 40 hours>20 but 30 hours

>10 but 20 hours 10 hours

$50$40$30

$20$10



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Step 1: InputNAME,OVERTIME,ABSENTStep 2: if (OVERTIME(2/3)*ABSENT > 40) then

PAYMENT 50else if (OVERTIME(2/3)*ABSENT > 30) then



PAYMENT 20else

PAYMENT10endifStep 3: Print Bonus for, NAME is $, PAYMENT



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02 algorithm, pseudocode and coding

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