programming and data structurecse.iitkgp.ac.in/~saptarshi/courses/pdstheory2019a/l1-intro.pdf ·...

ProgrammingandDataStructure

Prof.IndranilSenGupta

DepartmentofComputerScience&Engg.IndianInstituteofTechnology

Kharagpur

SomeGeneralAnnouncements

Autumn Semester2019 Programming and DataStructure 3

AbouttheCourse

• WillbeconductedwithaL-T-Pratingof3-0-0.

• LaboratorywithaL-T-Pof0-1-3.

• Evaluation inthetheorycourse:– Mid-semester 30%– End-semester 50%– Twoclasstestsandattendance 20%


CourseMaterials

• Theslidesforthelectureswillbemadeavailableontheweb(inPDFform).http://cse.iitkgp.ac.in/~saptarshi/

courses/pdstheory2019a/

• Allimportantannouncementswillbeputuponthewebpage.


ATTENDANCEINTHECLASSESISMANDATORY

Studentshavingpoorattendancewillbepenalizedintermsofthefinalgrade.


Text/ReferenceBooks&Notes

1. TheCProgrammingLanguage(2nd orhigheredition)Kernighan&Ritchie,Prentice-HallofIndia

2. ProgrammingwithC(2nd orhigheredition)B.S.Gottfried,Schaum’sOutlineSeries,TataMcGraw-Hill

3. ProgramminginANSIC(2nd orhigheredition)E.Balagurusamy,TataMcGraw-Hill,NewDelhi

4. DatastructuresS.Lipschutz,Schaum’sOutlineSeries,TataMcGraw-Hill

5. DatastructuresusingCandC++(2nd orhigheredition)Y.Langsam,M.J.Augenstein,A.M.Tanenbaum,Prentice-HallofIndia

6. http://cse.iitkgp.ac.in/~pds/notes/

Introduction


WhatisaComputer?

CentralProcessing

Unit(CPU)

InputDevice

OutputDevice

MainMemory

StoragePeripherals

It is a machine which can accept data, process them, and output results.


• CPU– Allcomputationstakeplacehereinorderforthecomputertoperformadesignatedtask.

– Ithasanumberofregisterswhichtemporarilystoredataandprograms(instructions).

– Ithascircuitrytocarryoutarithmeticandlogicoperations,takedecisions,etc.

– Itretrievesinstructionsfromthememory(fetch),interprets(decode)them,andperformstherequestedoperation(execute).


• MainMemory– Usessemiconductortechnology.– Memorysizesintherangeof4to16Gbytesaretypicaltoday.

– Somemeasurestoberemembered• 1K(kilo) =210 (=1024)• 1M(mega) =220 (=onemillionapprox.)• 1G(giga) =230 (=onebillionapprox.)• 1T(tera) =240 (=onetrillionapprox.)


• InputDevice– Keyboard,Mouse,Scanner

• OutputDevice– Monitor,Printer

• StoragePeripherals– MagneticDisks:harddisk,floppydisk

• Allowsdirect(semi-random)access– OpticalDisks:CDROM,CD-RW,DVD,BlueRay

• Allowsdirect(semi-random)access– FlashMemoryandSolidStateDrive

• Allowsdirectaccess– MagneticTape:DAT

• Onlysequentialaccess


Howdoesacomputerwork?

• Storedprogramconcept.– Maindifferencefromacalculator.

• Whatisaprogram?– Setofinstructionsforcarryingoutaspecifictask.

• Whereareprogramsstored?– Insecondarymemory,whenfirstcreated.– Broughtintomainmemory,duringexecution.


NumberSystem::TheBasics

• Weareaccustomedtousingtheso-calleddecimalnumbersystem.– Tendigits::0,1,2,3,4,5,6,7,8,9– Everydigitpositionhasaweightwhichisapowerof10.

• Example:234 =2x102 +3x101 +4x100

250.67=2x102 +5x101 +0x100 +6x10-1 +7x10-2


Contd.

• Adigitalcomputerisbuiltoutoftinyelectronicswitches.– Fromtheviewpointofeaseofmanufacturingandreliability,suchswitchescanbeinoneoftwostates,ONandOFF.

– Aswitchcanrepresentadigitintheso-calledbinarynumbersystem,0and1.

• Acomputerworksbasedonthebinarynumbersystem.

• Binarynumbersystem– Twodigits::0and1– Everydigitpositionhasaweightwhichisapowerof2.

• Example:1110=1x23 +1x22 +1x21 +0x20

=14(indecimal)



ConceptofBitsandBytes

• Bit– Asinglebinarydigit(0or1).

• Nibble– Acollectionoffourbits(say,0110).

• Byte– Acollectionofeightbits(say,01000111).

• Word– Dependsonthecomputer.– Typically4or8bytes(thatis,32or64bits).


Contd.

• Ank-digitdecimalnumber– Canexpressunsignedintegersintherange0to10k – 1.

• Fork=3,from0to999.

• Ank-bitbinarynumber– Canexpressunsignedintegersintherange0to2k – 1.

• Fork=8,from0to255.• Fork=10,from0to1023.


ClassificationofSoftware

• Twocategories:1. ApplicationSoftware

• Usedtosolveaparticularproblem.• Editor,financialaccounting,weatherforecasting,

mathematicaltoolbox,etc.

2. SystemSoftware• Helpsinrunningotherprograms.• Compiler,operatingsystem,etc.


ComputerLanguages

• MachineLanguage– Expressedinbinary.

• 10110100maymeanADD,01100101maymeanSUB,etc.

– Directlyunderstoodbythecomputer.

– Notportable;variesfromonemachinetypetoanother.• Programwrittenforonetypeofmachinewillnotrunonanothertypeofmachine.

– Difficulttouseinwritingprograms.


Contd.

• AssemblyLanguage– Mnemonicformofmachine language.

– Easiertouseascomparedtomachine language.• Forexample,use“ADD” insteadof“10110100”.

– Notportable(likemachinelanguage).

– Requiresatranslatorprogramcalledassembler.

AssemblerAssemblylanguageprogram

Machinelanguageprogram


Contd.

• Assemblylanguageisalsodifficulttouseinwritingprograms.– Requiresmanyinstructionstosolveaproblem.

• Example:Findtheaverageofthreenumbers.MOV A,X ;A=XADD A,Y ;A=A+YADD A,Z ;A=A+ZDIV A,3 ;A=A/3MOV RES,A ;RES=A

In C,

RES = (X + Y + Z) / 3


High-LevelLanguage

• Machinelanguageandassemblylanguagearecalledlow-levellanguages.– Theyareclosertothemachine.– Difficulttouse.

• High-levellanguagesareeasiertouse.– Theyareclosertotheprogrammer.– Examples:

• Fortran,C,C++,Java,Python.

– Requiresanelaborateprocessoftranslation.• Usingasoftwarecalledcompiler.

– Theyareportableacrossplatforms.


Compiler Objectcode Linker

Library

HLLprogram

Executablecode

gcccompilerwillbeusedinthelabclasses


OperatingSystems

• Makesthecomputereasytouse.– Basicallythecomputerisverydifficulttouse.– Understandsonlymachinelanguage.

• Operatingsystemsmakesthetaskoftheuserseasier.

• Categoriesofoperatingsystems:– Singleuser– Multiuser(Timesharing,Multitasking,Realtime)


Contd.

• Popularoperatingsystems:– Windows: single-usermultitasking– Unix: multi-user– Linux: afreeversionofUnix

• ThelaboratoryclasseswillbebasedonLinux.


Contd.

• Question:– Howmanyuserscanworkonthesamecomputer?

• Computersconnectedinanetwork.

• Manyusersmayworkonacomputer.– Overthenetwork.– Atthesametime.– CPUandotherresourcesaresharedamongthedifferentprograms.• Calledtimesharing.• Oneprogramexecutesatatime.

BasicProgrammingConcepts


SomeTerminologies

• Algorithm/Flowchart/Pseudo-code– Astep-by-stepprocedureforsolvingaparticularproblem.

– Shouldbeindependentoftheprogramminglanguage.

• Program– Atranslationofthealgorithm/flowchart intoaformthatcanbeprocessedbyacomputer.

– Typicallywritteninahigh-levellanguagelikeC,C++,Java,etc.

FirstLookataCProgram

/* Program to compute the area of a circle */#include <stdio.h> /* Compulsory, for library files */

main() /* Function heading */{

float radius, area; /* Declare variables */scanf (ʺ%fʺ, &radius); /* Read radius */area = 3.14159 * radius * radius;printf (ʺArea = %fʺ, area); /* Output to screen */

}


Input: 10Output: Area = 314.158997


VariablesandConstants

• Mostimportantconceptforproblemsolvingusingcomputers.

• Alltemporaryresultsarestoredintermsofvariablesandconstants.– Thevalueofavariablecanbechanged.– Thevalueofaconstantdonotchange.

• Wherearetheystored?– Inmainmemory.


Contd.

• Howdoesmemorylooklike(logically)?– Asalistofstoragelocations,eachhavingauniqueaddress.

– Variablesandconstantsarestoredinthesestoragelocations.

– Variableislikeahouse,andthenameofavariableisliketheaddress ofthehouse.• Differentpeoplemayresideinthehouse,whichislikethecontents ofavariable.


Memorymap

Address0Address1Address2Address3Address4Address5Address6

AddressN-1

Everyvariableismappedtoaparticularmemoryaddress


VariablesinMemory

10

20

21

105

MemorylocationallocatedtoavariableX

X=10

X=20

X=X+1

X=X*5

Instructionexecuted

Time


VariablesinMemory(contd.)

20

20

18

18

Variable

XY

X=20

Y=15

X=Y+3

Y=X/6

Instructionexecuted

?

15

15

3

Time

Datatypes

• Threecommondatatypesused:– Integer ::canstoreonlywholenumbers

Examples:25,-56,1,0

– Floating-point ::canstorenumberswithfractionalvalues.Examples:3.14159,-12345.345,2.65E12,2.35E-25

– Character ::canstoreasinglecharacterExamples:‘A’,‘a’,‘*’,‘3’,‘ ’,‘+’


DataTypes(contd.)

• Howaretheystoredinmemory?– Integer::

• 16bits• 32bits

– Float::• 32bits• 64bits

– Char::• 8bits(ASCIIcode)• 16bits(UNICODE,usedinJava)


Actualnumberofbitsvariesfromonecomputertoanother


Problemsolving(TypicalFlow)

• Step1:– Clearlyspecifytheproblemtobesolved.

• Step2:– Drawflowchartorwritealgorithm.

• Step3:– Convertflowchart(algorithm)intoprogramcode.

• Step4:– Compiletheprogramintoobjectcode.

• Step5:– Executetheprogram.


Flowchart:basicsymbols

Computation

Input / Output

Decision Box

Start / Stop


Contd.

Flow of control

Connector


Example1:Adding threenumbers

READA,B,C

S=A+B+C

OUTPUTS

STOP

START


Example2:Largeroftwonumbers

START

STOP

READX,Y

OUTPUTY

ISX>Y?

OUTPUTX

STOP

YES NO


Example3:Largestofthreenumbers

START

READX,Y,Z

ISLAR>Z?

ISX>Y?

LAR=X LAR=Y

OUTPUTLAR OUTPUTZ

STOP STOP

YES

YES

NO

NO


Example4:SumoffirstNnaturalnumbers

START

READN

SUM=0COUNT=1

SUM=SUM+COUNT

COUNT=COUNT+1

ISCOUNT>N? OUTPUTSUM

STOP

YESNO


Example5:SUM=12 +22 +32 +N2

START

READN

SUM=0COUNT=1

SUM=SUM+COUNT*COUNT

COUNT=COUNT+1


STOP

YESNO


Example6:SUM=1.2+2.3+3.4+toNterms

START

READN

SUM=0COUNT=1

SUM=SUM+COUNT*(COUNT+1)

COUNT=COUNT+1


STOP

YESNO


Example7:ComputingFactorial

START

READN

PROD=1COUNT=1

PROD=PROD*COUNT

COUNT=COUNT+1

ISCOUNT>N? OUTPUTPROD

STOP

YESNO


Example8:Computingex seriesuptoNterms

START

READX, N

TERM=1SUM=0

COUNT=1

SUM=SUM+TERMTERM=TERM*X/COUNT

COUNT=COUNT+1


STOP

YESNO


Example9:Computingex seriesupto4decimalplaces

START

READX

TERM=1SUM=0

COUNT=1

SUM=SUM+TERMTERM=TERM*X/COUNT

COUNT=COUNT+1

ISTERM<0.0001? OUTPUTSUM

STOP

YESNO


Example10:Rootsofaquadraticequation

ax2 +bx+c=0

TRYYOURSELF


Example11:Gradecomputation

MARKS≥ 90è Ex89≥MARKS≥ 80è A79≥MARKS≥ 70è B69≥MARKS≥ 60è C59≥MARKS≥ 50è D49≥MARKS≥ 35è P34≥MARKSè F


GradeComputation (contd.)

START

READMARKS

OUTPUT“Ex”

MARKS≥ 90? MARKS≥ 80? MARKS≥ 70?

OUTPUT“A” OUTPUT“B”

STOPSTOPSTOP

A

YESYESYES

NONONO


MARKS≥ 60?

STOP

OUTPUT“C”

A MARKS≥ 50? MARKS≥ 35?

OUTPUT“D” OUTPUT“P” OUTPUT“F”

STOP STOP STOP

YESYESYES

NONONO

ProgramminginC


SampleCprogram#1

#include <stdio.h>main()

{printf (ʺ\n Our first look at a C program \nʺ);

}


SampleCprogram#2

/* Compute the sum of two integers */


{int a, b, c;a = 10;b = 20;c = a + b;printf (ʺ\n The sum of %d and %d is %d\nʺ, a,b,c);

}


SampleCprogram#3

#include <stdio.h>

/* FIND THE LARGEST OF THREE NUMBERS */

main(){

int a, b, c;scanf (ʺ%d %d %dʺ, &a, &b, &c);if ((a>b) && (a>c)) /* Composite condition check */

printf (ʺ\n Largest is %dʺ, a);else

if (b>c) /* Simple condition check */printf (ʺ\n Largest is %dʺ, b);

elseprintf (ʺ\n Largest is %dʺ, c);

}

SampleCprogram#4


#include <stdio.h>#define PI 3.1415926

/* Compute the area of a circle */main()

{float radius, area;float myfunc (float radius);

scanf (ʺ%fʺ, &radius);area = myfunc (radius);printf (ʺ\n Area is %f \nʺ, area);

}

float myfunc (float r){

float a;a = PI * r * r;return (a); /* return result */

}


IntroductiontoC

• Cisageneral-purpose,structuredprogramming language.– Alsocontainsadditionalfeatureswhichallowittobeusedatalower

level.

• Ccanbeusedforapplications programmingaswellasforsystemsprogramming.

• Thereareonly32keywordsanditsstrengthliesinitsbuilt-infunctions.

• Cishighlyportable,sinceitrelegatedmuchcomputer-dependentfeaturestoitslibraryfunctions.


HistoryofC

• Originallydevelopedinthe1970’sbyDennisRitchieatAT&TBellLaboratories.

• Popularitybecamewidespreadbythemid1980’s,withtheavailabilityofcompilersforvariousplatforms.

• StandardizationhasbeencarriedouttomakethevariousCimplementationscompatible.– AmericanNationalStandards Institute(ANSI)– GNU


StructureofaCprogram

• EveryCprogramconsistsofoneormorefunctions.– Oneofthefunctionsmustbecalledmain.– Theprogramwillalwaysbeginbyexecutingthemainfunction.

• Eachfunctionmustcontain:– Afunctionheading,whichconsistsofthefunctionname,followedbyanoptionallistofarguments enclosedinparentheses.

– Alistofargumentdeclarations.– Acompoundstatement,whichcomprisestheremainderofthefunction.


Contd.

• Eachcompoundstatementisenclosedwithinapairofbraces:‘{‘ and‘}’– Thebracesmaycontaincombinations ofelementarystatementsandothercompoundstatements.

• Commentsmayappearanywhereinaprogram,enclosedwithindelimiters‘/*’ and‘*/’.– Example:

a=b+c;/*ADDTWONUMBERS*/


ExampleofaFunction

/* Compute the sum of two integers */// You can also give comments like this


{int a, b, c;

a = 10;b = 20;c = a + b;printf (ʺ\n The sum of %d and %d is %d\nʺ, a,b,c);

}


DesirableProgrammingStyle

• Clarity– Theprogramshouldbeclearlywritten.– Itshouldbeeasytofollowtheprogramlogic.

• Meaningfulvariablenames– Makevariable/constantnamesmeaningfultoenhanceprogram

clarity.• ‘area’ insteadof‘a’• ‘radius’ insteadof‘r’

• Programdocumentation– Insertcommentsintheprogramtomakeiteasytounderstand.– Neverusetoomanycomments.


Contd.

• Programindentation– Useproperindentation.– Structureoftheprogramshouldbeimmediatelyvisible.


IndentationExample#1::GoodStyle

#include <stdio.h>#define PI 3.1415926/* Compute the area of a circle */

main(){

float radius, area;float myfunc (float radius);

scanf (ʺ%fʺ, &radius);area = myfunc (radius);printf (ʺ\n Area is %f \nʺ, area);

}

float myfunc (float r){

float a;a = PI * r * r;return (a);

/* return result */}


IndentationExample#1::BadStyle

#include <stdio.h>#define PI 3.1415926/* Compute the area of a circle */main(){float radius, area;float myfunc (float radius);scanf (ʺ%fʺ, &radius);area = myfunc (radius);printf (ʺ\n Area is %f \nʺ, area);}

float myfunc (float r){float a;a = PI * r * r;return (a);

/* return result */}


IndentationExample#2::GoodStyle

#include <stdio.h>

/* FIND THE LARGEST OF THREE NUMBERS */

main(){

int a, b, c;scanf (ʺ%d %d %dʺ, &a, &b, &c);if ((a>b) && (a>c)) /* Composite condition check */

printf (ʺ\n Largest is %dʺ, a);else

if (b>c) /* Simple condition check */printf (ʺ\n Largest is %dʺ, b);

elseprintf (ʺ\n Largest is %dʺ, c);

}


IndentationExample#2::BadStyle

#include <stdio.h>/* FIND THE LARGEST OF THREE NUMBERS */main(){int a, b, c;scanf (ʺ%d %d %dʺ, &a, &b, &c);if ((a>b) && (a>c))/* Composite condition check */printf (ʺ\n Largest is %dʺ, a);elseif (b>c)/* Simple condition check */printf (ʺ\n Largest is %dʺ, b);elseprintf (ʺ\n Largest is %dʺ, c);}


TheCCharacterSet

• TheClanguagealphabet:– Uppercaseletters‘A’ to‘Z’– Lowercaseletters‘a’ to‘z’– Digits‘0’ to‘9’– Certainspecialcharacters:

! # % ^ & * ( )

- _ + = ~ [ ] \

| ; : ‘ “ { } ,

. < > / ? blank


IdentifiersandKeywords

• Identifiers– Namesgiventovariousprogramelements(variables,constants, functions,etc.)

– Mayconsistofletters,digits andtheunderscore (‘_’)character,withnospacebetween.

– Firstcharactermustbealetter.– Anidentifiercanbearbitrarylong.

• SomeCcompilersrecognizeonlythefirstfewcharactersofthename(16or31).

– Casesensitive• ‘area’,‘AREA’ and‘Area’ arealldifferent.


Contd.

• Keywords– Reservedwordsthathavestandard,predefinedmeaningsinC.

– Cannotbeusedasidentifiers.– OKwithincomments.– StandardCkeywords:

auto break case char const continue default do

double else enum extern float for goto if

int long register return short signed sizeof static

struct switch typedef union unsigned void volatile while


ValidandInvalidIdentifiers

• ValididentifiersXabcsimple_interesta123LISTstud_nameEmpl_1Empl_2avg_empl_salary

• Invalididentifiers10abcmy-nameʺhelloʺsimple interest(area)%ratedoublefor

Autumn Semester2019 Programming and DataStructure

DataTypesinC

int ::integerquantityTypicallyoccupies4bytes(32bits)inmemory.

char ::singlecharacterTypicallyoccupies1byte(8bits)inmemory.

float ::floating-pointnumber(anumberwithadecimalpoint)

Typicallyoccupies4bytes(32bits)inmemory.

double ::double-precisionfloating-pointnumberTypicallyoccupies8bytes(64bits)inmemory.

73


Contd.

• Someofthebasicdatatypescanbeaugmentedbyusingcertaindatatypequalifiers:– short– long– signed– unsigned

• Examples:short int flag;long int result;unsigned int count, age;


SomeExamplesofDataTypes

• int0,25,–156,12345,–99820

• char‘a’,‘A’,‘*’,‘/’,‘ ’

• float23.54,–0.00345,25.02.5E12,1.234e–5

Eoremeans“10tothepowerof”


Constants

Constants

NumericConstants

CharacterConstants

stringsinglecharacter

floating-pointinteger


IntegerConstants

• Consistsofasequenceofdigits,withpossiblyaplusoraminussignbeforeit.– Embeddedspaces,commasandnon-digitcharactersarenotpermittedbetweendigits.

• Maximumandminimumvalues(for32-bitrepresentations)

Maximum::+2147483647(231 – 1)Minimum::– 2147483648(– 231)

<For2’scomplementrepresentation>


Floating-pointConstants

• Cancontainfractionalparts.• Verylargeorverysmallnumberscanberepresented.

23000000canberepresentedas2.3e7

• Twodifferentnotations:1. Decimalnotation

25.0,0.0034,.84,-2.234

2. Exponential (scientific)notation3.45e23,0.123e-12,123E2 emeans“10tothe

powerof”


SingleCharacterConstants

• Containsasinglecharacterenclosedwithinapairofsinglequotemarks.– Examples::‘2’,‘+’,‘Z’

• Somespecialbackslashcharacters‘\n’ newline‘\t’ horizontaltab‘\’’ singlequote‘\”’ doublequote‘\\’ backslash‘\0’ null


StringConstants

• Sequenceofcharactersenclosedindoublequotes.– Thecharactersmaybeletters,numbers,specialcharactersandblankspaces.

• Examples:“nice”,“GoodMorning”,“3+6”,“3”,“C”

• Differencesfromcharacterconstants:– ‘C’ and“C” arenotequivalent.– ‘C’ hasanequivalentintegervaluewhile“C” doesnot.


Variables

• Itisadatanamethatcanbeusedtostoreadatavalue.

• Unlikeconstants,avariablemaytakedifferentvaluesinmemoryduringexecution.

• Variablenamesfollowthesamenamingconventionforidentifiers.

Examples ::temp,speed,name2,current,my_salary


Example

int a, b, c;char x;

a = 3;b = 50;c = a – b;x = ‘d’;

b = 20;a = a + 1;x = ‘G’;


DeclarationofVariables

• Therearetwopurposes:– Ittellsthecompilerwhatthevariablenameis.– Itspecifieswhattypeofdatathevariablewillhold.

• Generalsyntax:data-typevariable-list;

• Examples:int velocity, distance;int a, b, c, d;float temp;char flag, option;


AFirstLookatPointers

• Avariableisassignedaspecificmemorylocation.– Forexample,avariablespeed isassignedmemorylocation1350.

– Alsoassumethatthememorylocationcontainsthedatavalue100.

– Whenweusethenamespeed inanexpression,itreferstothevalue100 storedinthememorylocation.

distance = speed * time;

• Thuseveryvariablehasanaddress inmemory,anditscontents.


Contd.

• InCterminology,inanexpressionspeed referstothecontents ofthememorylocation.&speedreferstotheaddress ofthememorylocation.

• Examples:printf (ʺ%f %f %fʺ, speed, time, distance);scanf (ʺ%f %fʺ, &speed, &time);


AnExample


{float speed, time, distance;

scanf (ʺ%f %fʺ, &speed, &time);distance = speed * time;printf (ʺ\n The distance traversed is: %f \nʺ,

distance);}


AssignmentStatement

• Usedtoassignvaluestovariables,usingtheassignmentoperator(=).

• Generalsyntax:variable_name=expression;

• Examples:velocity = 20;b = 15; temp = 12.5; A = A + 10;v = u + f * t;s = u * t + 0.5 * f * t * t;


Contd.

• Avaluecanalsobeassignedtoavariableatthetimethevariableisdeclared.

int speed = 30;char flag = ‘y’;

• Severalvariablescanbeassignedthesamevalueusingmultipleassignmentoperators.

a = b = c = 5;flag1 = flag2 = ‘y’;speed = flow = 0.0;


OperatorsinExpressions

Operators

ArithmeticOperators

RelationalOperators

LogicalOperators


ArithmeticOperators

• Addition:: +• Subtraction:: –• Division:: /• Multiplication:: *• Modulus:: %


Examples

distance = rate * time ;

netIncome = income - tax ;

speed = distance / time ;

area = PI * radius * radius;

y = a * x * x + b*x + c;

quotient = dividend / divisor;

remain = dividend % divisor;


Contd.

• Supposex andy aretwointegervariables,whosevaluesare13 and5 respectively.

x + y 18

x – y 8

x * y 65

x / y 2

x % y 3


OperatorPrecedence

• Indecreasingorderofpriority1. Parentheses::()2. Unaryminus::–53. Multiplication,Division,andModulus4. AdditionandSubtraction

• Foroperatorsofthesamepriority,evaluationisfromlefttoright astheyappear.

• Parenthesismaybeusedtochangetheprecedenceofoperatorevaluation.


Examples:Arithmeticexpressions

a+b*c– d/e è a+(b*c)– (d/e)

a*– b+d%e– f è a*(– b)+(d%e)– f

a– b+c+d è (((a– b)+c)+d)

x*y*z è ((x*y)*z)

a+b+c*d*e è (a+b)+((c*d)*e)


IntegerArithmetic

• Whentheoperandsinanarithmeticexpressionareintegers,theexpressioniscalledintegerexpression,andtheoperationiscalledintegerarithmetic.

• Integerarithmeticalwaysyieldsintegervalues.

• Examples:(12 + 3) / 6 gives the value 2(2 / 3) * 3 gives the value 0(12 * 3) / 7 + 3 * 2 gives the value 11


RealArithmetic

• Arithmeticoperationsinvolvingonlyrealorfloating-pointoperands.

• Sincefloating-pointvaluesareroundedtothenumberofsignificantdigitspermissible,thefinalvalueisanapproximationofthefinalresult.

1.0/3.0*3.0willhavethevalue0.99999 andnot1.0

• Themodulusoperatorcannotbeusedwithrealoperands.


Mixed-modeArithmetic

• Whenoneoftheoperandsisintegerandtheotherisreal,theexpressioniscalledamixed-mode arithmeticexpression.

• Ifeitheroperandisoftherealtype,thenonlyrealarithmeticisperformed,andtheresultisarealnumber.

25 / 10 gives the value 225 / 10.0 gives the value 2.5

• Somemoreissueswillbeconsideredlater.


TypeCasting

• Temporarilyconvertthetypeofavariablebeforebeingusedinanexpression.– Expressedbyspecifyingthedesired typeinparenthesisbeforethevariable/expression.

• Examples:int a = 10, b = 4, c; float x, y;x = (float) a / b; /* x will be 2.5 */y = (float) (a / b); /* y will be 2.0 */c = (int) x * 4; /* c will be 8 */a = (int) (x * 4); /* a will be 10 */


RelationalOperators

• Usedtocomparetwoquantities.

• Theresultofcomparison is“true” or“false”.– Thevalue0isconsideredas“false”,andanynon-zerovalueas“true”.

< is less than> is greater than<= is less than or equal to>= is greater than or equal to== is equal to!= is not equal to


Examples

10 > 20 is false25 < 35.5 is true12 > (7 + 5) is false

• Whenarithmeticexpressionsareusedoneithersideofarelationaloperator,thearithmeticexpressionswillbeevaluatedfirstandthentheresultscompared.

a + b > c – d is the same as (a+b) > (c+d)


Examples

• SamplecodesegmentinC:

if (x > y)printf (ʺ%d is larger\nʺ, x);

elseprintf (ʺ%d is larger\nʺ, y);

if (1) /* will be always true */…………


LogicalOperators

• TherearetwologicaloperatorsinC(alsocalledlogicalconnectives).

&&è LogicalAND||è LogicalOR

• Whattheydo?– Theyactuponoperandsthatarethemselveslogicalexpressions.

– Theindividual logicalexpressionsgetcombined intomorecomplexconditionsthataretrue orfalse.


– LogicalAND• Resultistrueifboththeoperandsaretrue.

– LogicalOR• Resultistrueifatleastoneoftheoperandsaretrue.

X Y X&&Y X||Y

FALSE FALSE FALSE FALSE

FALSE TRUE FALSE TRUE

TRUE FALSE FALSE TRUE

TRUE TRUE TRUE TRUE

• Examples:

if ((i > 2) && (i < 10))printf (ʺ\n i lies between 3 and 9ʺ);

if ((flag == ’A’) || (flag == ’a’)printf (ʺ\n Either lower or uppercase Aʺ);



Input/Output

• printf– Performsoutputtothestandardoutputdevice(typicallydefinedtobethescreen).

– Itrequiresaformatstringinwhichwecanspecify:• Thetexttobeprintedout.• Specificationsonhowtoprintthevalues.

printf(ʺThenumberis%d.\nʺ,num);• Theformatspecification%d causesthevaluelistedaftertheformatstringtobeembeddedintheoutputasadecimalnumberinplaceof%d.

• Outputwillappearas:Thenumberis125.


• scanf– Performsinputfromthestandardinputdevice,whichisthekeyboardbydefault.

– Itrequiresaformatstringandalistofvariablesintowhichthevaluereceivedfromtheinputdevicewillbestored.

– Itisrequiredtoputanampersand(&)beforethenamesofthevariables.

scanf("%d",&size);scanf("%c",&nextchar);scanf("%f",&length);scanf(“%d%d”,&a,&b);

programming and data structurecse.iitkgp.ac.in/~saptarshi/courses/pdstheory2019a/l1-intro.pdf ·...

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