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Introduction to C Programming

Program design

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CT018-3-1 Introduction To C Programming Program Design

Topic & Structure of the lesson

In this chapter you will learn about:

Problem Solving

Algorithm

Pseudocodes

Flowcharts

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Learning Outcomes

If you have mastered this topic, you should be ableto use the following terms correctly in your

assignments:

Algorithm

Pseudocode

Flowchart

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Problem Solving

First:

ou have tounderstandthe problem!

U!"#ST$!I% T" P#O'L"(

"hat is the un#nown$ "hat are the data$"hat is the condition$

Is it possible to satisfy the condition$Is thecondition sufficient to determine theun#nown$%r is it sufficient$%r &edundant$%r Contradictory$

'raw a figure!Introduce suitablenotation!Separate the various parts of thecondition!Can you write them down$

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Problem Solving

Second:

Find the connectionbetween the data and

the un#nown!Au(iliary problemsmay be devised ifneeded!

ou should obtaineventually a plan ofthe solution!

!")ISI% $ PL$

)ave you seen it before$ %r have youseen the same problem in slightly differentform$

'o you #now a related problem$*oo# at the un#nown+ ry to thin# of afamiliar problem having the same or similarun#nown! Split the problem into smaller,simple sub-problems! If you cannot solve

the proposed problem try to solve firstsome related problem! %r solve moregeneral problem! %r special case of theproblem! %r solve the part of the problem!

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Problem Solving

hird:

Carry out yourplan!

*$##+I% OUT T" PL$

Carrying out your plan of the solution,chec#each step! Can you see clearly that step iscorrect$ Can you prove that it is correct$

Fourth:

.(amine thesolutionobtained!

LOO,I% '$*,

Can you chec# the result$ Can you derivethe result differently$ Can you use theresult, or the method, for some otherproblem$

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7/35CT018-3-1 Introduction To C Programming Program Design

$lgorithm

Algorithmic problem:

Any problem whose solution can be

e(pressed as a set of e(ecutable instructions!

Algorithm:

A well defined computational procedure

consisting of a set of instructions, that ta#essome value or set of values, as input, and

produces some value or set of values, as

output.

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*haracteristics of an $lgorithm

.ach step of an algorithm must be e(act, preciouslyand ambiguously described!

It must terminate, i!e! it contains a finite number ofsteps!

It must be effective, i!e!!, produce the correct output!

It must be general, i!e!! to solve every instance of the

problem! An Algorithm is implemented in someprogramming language.

program = Algorithm + Data Structures.

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Problem Solving

Slide 26 (of 80)

/ow that we have an exact idea about how the

problem is solved, let us represent this in a clearer

manner, using the defining diagram!

Input Processing %utput

0alue1

0alue2

Sum

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Problem Solving

Slide 2 (of 80)

he ne(t step is to identify the actual processingsteps re3uired to convert the input to become the

output!


0alue1

0alue2

Sum14 &ead 0alue1, 0alue2

24 Calculate Sum

54 'isplay Sum

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$lgorithm !evelopment

Slide 28 (of 80)

%nce the defining diagram has been

developed, the ne(t logical step is to developthe algorithm6which is much more detailed4!


0alue1

0alue2

Sum14 &ead 0alue1, 0alue2

24 Calculate Sum

54 'isplay Sum

he developed processing steps have to be more

detailed in the algorithm!

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Operators

Slide 2! (of 80)

he basic mathematical operators used in algorithmsare as follows:-

7 addition

- subtraction

8 multiplication

9 division

assignment

6 4 brac#ets for grouping calculations

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$lgorithm !evelopment

Slide 30 (of 80)

.(ample of an algorithm 6using pseudocodes4 which

can be used to carry out the tas#s outlined in the

defining diagram is as follows:-

14 &ead 0alue1, 0alue2

24 CalculateSum 0alue1 7 0alue2

54 'isplay Sum

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Pseudocoding

Slide 31 (of 80)

A Pseudocode language is semiformal, .nglish-li#elanguage with a limited vocabulary that can be usedto design and describe algorithms!

he pseudocode language can be used for:

'esigning algorithms

Communicating algorithms as programs

Implementing algorithms as programs

'ebugging logic errors in program

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Program -lowcharts

Slide 62 (of 80)

As humans are more inclined towards

understanding diagrams and pictures rather

than words, pseudocodes tends to becometedious to understand if too lengthy!

Program flowcharts, because they are

represented graphically, ma#es understandingeasier!

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-lowcharting

Slide 66 (of 80)

Another techni3ue used in designingand representingalgorithms!

Alternative to pseudocoing

A pseudocode description is verbal, a flowchart isgraphicalin nature!

!efinition:

A flowchart is a graph consisting of geometrical shapesthat are connected by flow lines!

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Program -lowcharts

Slide 63 (of 80)

he following are the commonly used

symbols for drawing program flowcharts!

terminator off-page

connector

process storage

decision

ma#ingdocument

input9output connector

arrowheads

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Pseudocode for the *ontrol Structures

Slide 32 (of 80)

The Se.uence *ontrol Structure:

he sequence control structureis a series of stepsor statements that are e(ecuted in the order in whichthey are written in an algorithm!

For .(ample:

read taxable income

read filing status compute income tax

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!ecision (a/ing

Slide 33 (of 80)

The Selection *ontrol Structure:

he selection control structure defines two courses ofaction, depending on the outcome of a condition! Acondition is an e(pression that, when evaluated, computesto either true or false!

Synta( is:

if condition

thenpart

else

elsepart

endif

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!ecision (a/ing

Slide 3 (of 80)

Commonly used relational operators in expressions:-

;

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!ecision (a/ing

Slide "0 (of 80)

Compound e(pressions can be representedusing the followingoperators:-

A/' .very e(pression must evaluate to be

truein order for the whole e(pression tobe true!

%& As long as any one of the e(pression

can be true, the entire IF statement willbe true!

/% he inverse 6opposite4 of the entire

e(pression!

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!ecision (a/ing 0 "1ample

Slide 38 (of 80)

A potential employer is waiting for you to give a reply 6on thespot4 about the ?ob offer with a salary of &@2! our

decision would be to only ta#e a ?ob worth more than

&@B! "hat would you say$

IF 6Salary>40004 )./Say .S+D

.*S.

Say /%+D

./'IF

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!ecision (a/ing 0 "1ample

Slide 3! (of 80)

Certain conditions may give rise to more thanone e(pression being evaluated! hese are

#nown as compound expressions!

.!g! ou are interested in ta#ing up a ?ob which

pays morethan &@B and that the company

must also provide a credit card!

IF 6Salary;B4 And 6CreditCard.S4 )./

a#e Eob++

./'IF

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#epetition

Slide "# (of 80)

#epetition *ontrol Structure:

he repetition control structure specifies a bloc# ofone or more statements that are repeatedly e(ecuteduntil a condition is satisfied!

Synta( is:

while condition

loopbod!

endwhile

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Looping *onstructs

Slide "6 (of 80)

*ooping constructs 6also #nown as repetition or

iterationconstructs4 are a #ind of construct found

in pseudocodes which allows statements 6or a

group of statements4 to be repeated!

he main reason why looping constructs are

provided is because most of the problems which

we encounter everyday re3uires some degree ofrepetition!

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Looping *onstructs

Slide "8 (of 80)

he looping constructs available in pseudocodes

are as follows:-

'%")I*.!!!./''%

F%&/.G

&.P.A!!!H/I*

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Looping *onstructs

Slide "! (of 80)

he format of the '%")I*.!!!./''% construct is shownbelow:-

'%")I*. 6expression4

:

:

:

./''%

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Looping *onstructs

Slide #0 (of 80)

he format of the F%&!!!/.G construct is shown below:-

F%& 6initiale % e(pression4 S.P increment

:

::

/.G

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Looping *onstructs

Slide #1 (of 80)

he format of the&.P.A!!!H/I* construct is

shown below:-

&.P.A:

:

:

H/I* 6expression4

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.(ample

!owhile2 "nddo

Slide ## (of 80)

Dowhile (income is less than 50000)

print nter taxa!le income"

should !e greater than or e#ual

to 50000$

read income

nddo

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$rray

Contiguous, homogeneous collection of data

values that share a common name!

lement - one value in an array!

%ndex 6subscript4 - an integer indicating a

position in an array! Array inde(es start with !

3 4 5 6 7 8 9 ;

1 2 55 BB 1L M 1N OO 2

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$rray 0 "1ample

&eplace every third element in the following

array with value 1!

/ote: /ame: numberQ Sie 6elements4 O

3 4 5 6 7 8 9

5 B 2 5 L N 1 N

3 4 5 6 7 8 9

1 B 2 1 L N 1 N

F%& 6inde( % N4 S.P 5

numberRinde( 1

/.G inde(

or

Set inde( to

F%& every third element in the number

replace e(isting value with 1

increase inde( by 5

./'F%&

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!esign

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!esign egin

&ead Amount

.nd

Amount;2!$

Calculate

ActualAmount 8 !O

Calculate

ActualAmount

/%.S

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Summary

An algorithmis a se3uence of a finite number of stepsarranged in a specific logical order that, when e(ecuted,produce the solution for a problem!

A pseudocodelanguage is a semiformal,.nglish-li#elanguage with a limited vocabulary that can be used todesign and describe algorithms!

$ -lowchartis a graphical representation of analgorithm!

Documents

02 03 Design