《计算机科学导论》课件Unit 9Programming Languages

?计算机科学导论?课件Unit9ProgrammingLanguages29-1Development9-2ProgramTranslation9-3Languages’LatestRanking,Categories

andFeatures9-4CommonConceptsofProgramming

Languages9-5NotoriousSoftwareErrors9-6ReferencesandRecommendedReading9-7Summary9-8PracticeSetOUTLINE5Development

Computerlanguageisthemediumofcommunicationbetweenmanandcomputer.Aprogramminglanguageisaformalconstructedlanguagedesignedtotransmitinstructionstoamachine,particularlyacomputer.Programminglanguageshaveevolvedtremendouslyfrommachinelanguage,andassemblylanguagestohigh-levellanguages.Ofcourse,naturallanguage

isthebestprogramminglanguageandalsoourfinalgoal.Figure9.1presentsatimelineforcomputerlanguages.

Figure9.1Developmentofcomputerlanguages6Machinelanguages

(1)Machinelanguages

Machinelanguagesareexecuteddirectlybyacomputer’sCPU(CentralProcessingUnit).Theyaretypicallyformulatedasbitpatterns,usuallyrepresentedinoctalorhexadecimal.Machine-languageprogramsarewrittenbyenteringaseriesofinstructionsintheirbinaryformwhichismadeofstreamsof0sand1s,andeachcomputerhasitsownmachinelanguage.Theonlyprogramminginstructionsthatacomputeractuallyexecutesarethosewrittenusingmachinelanguage,theinstructionsbuiltintothehardwareofaparticularcomputer.Machinelanguagehasthefeaturesofflexibility,directexecutionandhigh-speed.

Note:Theonlylanguagethatcomputerisabletounderstandismachinelanguage.

7Machinelanguages

MachinelanguageinstructionsFinishedoperation0001000000100000Getanintegerfromthememoryunit

20,thensetittoregister

A0011000000100001Addthevalueofthememoryunit21toregisterA0010000000100010StorethevalueofregisterAtothememoryunit220000000000000000FinishtheprogramTable9.1MachinelanguageprogramforaddingtwointegersTable9.1showsthemachinelanguageprogramtoaddtwointegers.8Assemblylanguages

(2)Assemblylanguages

PeopleuseEnglishstrings,whichareeasiertoread,torepresentthemachinecodeandintroducetheassemblylanguage.Assemblylanguageusesmnemoniclettercodestorepresenteachmachine-languageinstruction.Theprogrammerusesthesemnemonicsinplaceofbinarydigits.Assemblylanguageallowsprogrammerstowriteinstructionsineasierways.However,theCPUcannotunderstandthissymboliclanguage,soithastobeassembledintomachinelanguagebeforethecomputercanexecuteit.Hence,itthendevelopedintotheassemblylanguage.Theassemblylanguageisadirectlyinvokedprocessor-oriented

programminglanguage.

Inassemblylanguage,useofmnemonicinsteadofmachineinstructionop-code,andaddresssymbolorlabelinsteadofinstructionoroperandaddress,enhancesthereadability

oftheprogramandreducesthedifficultyofpreparation.

9Assemblylanguages Theprocessoftranslatingtheprograminassemblylanguageintomachinecodeiscalledassemblyprocess,asshowninFigure9.2.

Figure9.2Assemblyprocess

Assembly

languageinstructionsFinishedoperationLOADXGetanintegerfromthememoryunitX,thensetittoregisterAADDYAddthevalueofthememoryunitYtoregisterASTORESUMStorethevalueofregisterAtothememoryunitSUMHALTFinishtheprogramTable9.2Assemblylanguageprogramforaddingtwointegers10High-levellanguages

(3)High-levellanguages

Eachinstructionoftheassemblylanguagerequiresseparatecoding,whichmeansinefficiencyforprogramming.Thus,inordertoimprovetheefficiencyofprogrammers,andmakethemfocusonapplicationsratherthancomputerhardware,thehigh-levellanguageswereintroducedanddeveloped.

Thehigh-levellanguageisnotspecifiedforaspecificlanguage,butincludesmanyprogramminglanguages,suchasBASIC(Beginner’sAll-purposeSymbolicInstructionCode),FORTRAN(FormulaTranslation),COBOL(CommonBusiness-OrientedLanguage),Pascal,C,VisualBasic,Perl,Python,PHP,HTML,FoxPro,Delphi,VisualC,C++,Java,C#(pronouncedasCsharp),LISP(ListProgramming),Prolog(ProgramminginLogic),andsoon.Thesyntaxandthecommandformatoftheselanguagesarenotidentical.

11High-levellanguages

Table9.3BasiclanguageprogramforaddingtwointegersTable9.3showstheBasiclanguageprogramforaddingtwointegers.BasiclanguagestatementsFinishedoperationx=3Addendx,valuation3y=4Addendy,valuation4Sum=x+yStorexandytothesum12Naturallanguages(4)NaturallanguagesThenaturallanguageisalanguagewhichisusedinoureverydaylife.Itisusedforcommunication,whetherbyspeech,signingorwriting.English,Chinese,andArabicareexamplesofnaturallanguagesandthesentence“Ilikeallprogramminglanguages〞isastatementofanaturallanguage.Naturallanguageprocessing(NLP)isafieldofcomputerscience,artificialintelligence(AI),andlinguisticsconcernedwiththeinteractionsbetweencomputersandhuman(natural)languages.

139-2ProgramTranslation

Theprogramswritteninoneofthehigh-levellanguages,iscalledasourceprogram.Itissavedastextfilecalledsourcefile.Thecomputerdoesn’tunderstandandexecutesuchprogramunlessitistranslatedintothemachinelanguage.Translationhastwodifferentmethods:compilationandinterpretation.Compilation:Thecompilerisaprogramthattranslatesthewholesourceprogramintoamachinelanguageprogramcalledanobjectprogram.ThisobjectprogramcanthenbelinkedwithsupportinglibrariesusingalinkertocreateanexecutablefilethatrunsdirectlyontheCPU.Figure9.3showsthetranslationprocessesofacompiler.

Interpretation:Theinterpreter【解释器】isaprogramthatreadseachstatementofasourceprograminsequence,analyzesitwhatitmeans,translatesitintothecorrespondingmachinecodeandthenimmediatelyexecutesit,andthengoesontothenextline.Aninterpreterisatranslatingprogramthattranslatesandexecutesthestatementsinsequence.14ProgramTranslation

Figure9.3Sourcecodecompilationprocess15LatestrankingProgramminglanguageparadigmsFeaturesofprogramminglanguages9-3Languages’LatestRanking,CategoriesandFeatures16LatestrankingItisdifficulttodeterminewhichprogramminglanguagesaremostwidelyused,becauseeverylanguagehasitsownfeatures.Forthesameapplication,Clanguagemayneedmorelinesofcode(LOC)thanPython,butitmaybemoreefficient.Somelanguagesareverypopularforspecifickindsofapplications.Forexample,COBOLisstillwidelyusedinthecorporatedatacenter,oftenonlargemainframes;Fortranisusedinengineeringapplications;Cisusedinembeddedapplicationsandoperatingsystems;andotherlanguagesareregularlyusedtowritespecificapplications.TheTIOBEProgrammingCommunityIndexhasbeenpublishedsince2001andupdatedmonthly.TheratingsarebasedonsearchingtheWebwithparticularphrasesthatincludelanguagenamesandcountingthenumberofhits.Table9.4showsthelatestrankinginJun,2021andthechangeincontrasttoJun,2021.

17Latestranking

Table9.4Programminglanguages’rankingJun2016Jun2015ProgrammingLanguageRatingsChange11Java20.794%+2.97%22C12.376%-4.41%33C++6.199%-1.56%46Python3.900%-0.10%54C#3.786%-1.27%68PHP3.227%+0.36%79JavaScript2.583%+0.29%812Perl2.395%+0.64%97VisualBasic.NET2.353%-0.82%1016Ruby2.336%+0.98%1111VisualBasic2.254%+0.41%1223Assemblylanguage2.119%+1.36%1310Delphi/ObjectPascal1.939%+0.07%1414Swift1.831%+0.39%155Objective-C1.704%-2.64%1613R1.540%+0.02%1715MATLAB1.447%+0.01%1817PL/SQL1.346%+0.12%1926D1.063%+0.45%2018COBOL1.048%+0.10%18Latestranking

Inadditiontothe20mostcommonlanguagesinthetableabove,therearealsomanyfamouslanguages,forexample,Fortran,Scratch,ABAP(AdvancedBusinessApplicationProgramming),Dart,SAS,Groovy,T-SQL(Transact-SQL),Lisp,Ada,Scala,Lua,Logo,Prolog,Scheme,RPG,LabVIEW,OpenEdgeABL(OpenEdgeAdvancedBusinessLanguage),Erlang,Haskell,Alice,Apex,Bash,F#,Q,LadderLogic,Rust,Awk,Go,FoxPro,VBScript,TypeScript,andsoon.Wewillnotgointodetailsonotherlanguages.19Programminglanguageparadigms

Computerlanguagescanbedividedintofourcategoriesaccordingtotheapproachtheyusetosolveaproblem:procedural(imperative)languages,object-orientedlanguages,functionallanguagesanddeclarativelanguages.Table9.5showsthecategoriesofprogramminglanguageswithexamples.

Computerlanguageparadigms

ProceduralFORTRAN/COBOL/BASIC/C/Pascal/AdaObject-orientedSmalltalk/C++/VisualBasic/C#/Java/Python/Ruby/JavaScript/Perl/PHP/Simula/Lua/R/ObjectiveC/TCL/IoFunctionalLISP/SchemeDeclarativeProlog/ErlangTable9.5Categoriesofprogramminglanguages20Programminglanguageparadigms

(1)Procedural(imperative)languages

Proceduralprogramming,derivedfromstructuredprogramming,isbasedupontheconceptofprocedure-call.Aproceduralprogramiscomposedofoneormoreunitsorproceduresormodules.Proceduresarealsocalledfunctions,routines,subroutines,ormethods.Theycontainaseriesofcomputationalstepstobeexecuted.Duringaprogram’sexecution,anygivenproceduremightbetriggered(called)atanypoint,byotherproceduresoritself.

TypicalexamplesofprocedurallanguagesareFORTRAN,COBOL,BASIC,C,PascalandAda.

21Programminglanguageparadigms(2)Object-orientedlanguages

Theobject-orientedprogramming(OOP)handlessomeinteractingobjects.Eachobjectisresponsibleforitsownactions.Intheproceduralprogramming,dataitemsareconsideredpassiveandaremanipulatedbytheprogram.Whileinobject-orientedprogramming,dataobjectsareactive.Theyhavetheirownactionsanddata,andtheexecutiondependsonthem.Objectsandtheactiontobeperformedontheseobjectsarebundledtogether,thusmakingeachobjectresponsibletoperformoneoftheactionswhenitreceivestheappropriatestimulusbysomeexternalevent.Theselanguagesallowtheprogrammerstoimplementalgorithmsasahierarchyofobjects.Object-orientedprogrammingachievesthreemainobjectivesofsoftwareengineering:reusability,flexibility,andscalability.Inordertostandardizethebehaviorsofobjects,eachobjectcanreceiveinformation,processdataandsendinformationtootherobjects.Thedesignconceptsofobject-orientedprogrammingincludeobjects,classes,methods,dataabstraction,inheritance,dynamicbinding,dataencapsulation,polymorphism,andmessagepassing.Theseconceptsconcretelyexpresstheideaofobject-orientedprogramming.

22Programminglanguageparadigms

Typicalexamplesofobject-orientedlanguagesareSmalltalk,C++,VisualBasic,C#,Java,Python,Ruby,JavaScript,Perl,PHP,SIMULA,LUA,ObjectiveC,TCL,IoandR.(3)FunctionallanguagesFunctionallanguagesdefineprogramsandsubroutinesasmathematicalfunctions.Inthiscontext,afunctionisablackboxthatmapsinputsintooutputs,dependingontheargumentsthatareinputtothefunction.Computationisexpressedasfunctions.Thesolutiontoaproblemisexpressedasfunctioncalls.Figure9.4showsafunctioninafunctionallanguage.

TypicalexamplesoffunctionallanguagesareLISPandScheme.

Figure9.4Afunctioninafunctionallanguage23Programminglanguageparadigms

(4)Declarativelanguages

Declarativelanguagedescribethelogicofacomputationratherthanexpressingitscontrolflow.Thisisincontrastwithprocedural(imperative)programming,whichneedsanexplicitlyprovidedalgorithmandhavetopassconsecutiveorderstoacomputer.Infact,all(pure)functionalandlogic-basedprogramminglanguagesaredeclarative.

TypicalexamplesofdeclarativelanguagesarePrologandErlang.24Featuresofprogramminglanguages

Table9.6showsthefeatures,applicationscenariosanddevelopmenttoolsofsomepopularprogramminglanguages.

Table9.6ProgramminglanguagesLanguageFeatureApplicationScenariosDevelopmentToolsJavaObject-oriented;Cross-platform;Multi-thread;Powerfulclasslibrary;Allkindsofwebdevelopment,especiallylargeenterpriseapplications.Eclipse/NetBeans/JBuilderCProcedure-oriented;Highperformance;Strongexpressionability;Highportability;Dynamicmemorymanagement;Mostoftheoperatingsystems,driversandtheunderlyingsoftwareVC6.0/VisualStudio/CodeBlocks/GccC++Object-Oriented;Flexible;Compatible;Highperformance;Standardtemplatelibrary;DynamicmemorymanagementLargeclientapplications,gamedevelopment,andtheunderlyingframework.VC6.0/VisualStudio/Code::Blocks/G++C#Object-oriented;Highscalability;Garbagecollection;CloselyintegratedwiththeWebVisualStudio/MonoDevelopPythonSimple;Clear;Powerfulclasslibrary;Dailyneedofsmalltools,includingscripttaskofsystemadministratorsPyCharm25Featuresofprogramminglanguages

Table9.6ProgramminglanguagesLanguageFeatureApplicationScenariosDevelopmentToolsPHPSever-Based;PerfectcombinationwithApacheandMySQL;Serverdevelopment,suchasUnix,Linux,WindowsAppserv/phpStudyVisualBasic.NETEasytolearnanduse;Visual-design;Powerfulclasslibrary;Interactivity;MultimediaVisualStudioJavaScriptSimple；Secure;Dynamic;Cross-platform;Almostallthefields,suchasWebandmobiledevelopmentSpket/Ixedit/KomodoEdit/EpicEditor;PerlComplexandflexibledatastructure;Simple;Powerfulpatternmatching;ManyStandardandthird-partymodules,Graphicaluserinterfaces(GUIs)developmentWxPerl/ActivePerl/PerlBuilder/PadreRubyCross-platform;Flexible;Scalable;Object-oriented;Powerfulrails;RapidwebdevelopmentRDT(RubyDevelopmentTools)/RadRails26Featuresofprogramminglanguages

Someimportantprogramminglanguagesforspecificareasaregivenbelow:(1)MathematicalAnalysisandProcessing:MATLAB,R,SAS

MATLAB(matrixlaboratory)isabusinessmathematicalsoftwareproducedbytheAmericanMathWorkscompany.Itcanachievealgorithmdevelopment,datavisualization,dataanalysisandnumericalcalculationofseniortechnicalcomputinglanguageandinteractiveenvironment,mainlyincludingtwomostofMATLABandSimulink.

Risacompletesetofdataprocessing,calculationanddrawingsoftwaresystem.Ithassomeuniquefeaturesthatmakeitverypowerfulandsimple,suchasdataprocessing,array

operation,statisticalanalysis,andstatisticalgraphics.SAS(StatisticsAnalysisSystem)ismainlyusedforstatisticalanalysis.Itcanreadindatafromcommonspreadsheets

anddatabasesandoutputtheresultsofstatisticalanalysesintables,graphs,andasRTF(RichTextFormat),HTML,andPDF(PortableDocumentFormat)

documents.

(2)ParallelComputingModel:CUDA,OpenACC,OpenMP,OpenCL27FeaturesofprogramminglanguagesThereisnospeciallanguageforparallelprogramming,butalotoflanguagesareusedinparallelcomputingmodel,suchasCUDA(ComputetheUnifiedDeviceArchitecture),OpenACC(OpenAccelerators),OpenMP(OpenMuti-processing),OpenCL(OpenComputingLanguage),andsoon.(3)Database:SQL(StructuredQueryLanguage),PL(SQL),Transact-SQL

SQLisastandardizedcomputerlanguagethatwasoriginallydevelopedbyIBMforquerying,alteringanddefiningrelationaldatabases,usingdeclarativestatements.

T-SQL(Transact-SQL)isMicrosoft’sandSybase'sproprietaryextensiontoSQLandiscentraltousingMicrosoftSQLServer.

PL/SQL(ProceduralLanguage/StructuredQueryLanguage)isOracle’sproceduralextensiontoSQLandtheOraclerelationaldatabase.

(4)DesigningfortheOSXandiOSoperatingsystems:Object-C,SwiftNativeapplicationofiOSmustbewritteninSwiftorObjective-C,whereassomeelementscanuseCorC++optionally.28Featuresofprogramminglanguages

(5)ArtificialIntelligence:Prolog,LISPProlog(ProgramminginLogic)isageneralpurposelogicprogramminglanguagemostwidelyusedinartificialintelligence.Itsprogrammingmethodismorelikeusinglogictodescribeprogramming,soitcandevelopmorequicklythananyotherlanguage.

LISPisagenerichigh-levelcomputerprogramminglanguage.Itisoneoftheoldesthighlevelprogramminglanguagesandcontinuestobepopularinthefieldofartificialintelligencetothepresentday.(6)AutomaticTesting:TCL(ToolCommandLanguage)

TCLismainlyusedforindividualandembeddedcompaniessuchasHuaweiandMaipu.(7)WebPageDevelopment:HTML,HTML5

HTML(HypertextMarkupLanguage)isthestandardmarkuplanguageusedtocreatewebpages,alongwithCSS(CascadingStyleSheets),andJavaScript.

HTML5isamarkuplanguageusedforstructuringandpresentingcontentontheWorldWideWeb.ItisthefifthandcurrentversionoftheHTMLstandard.HTML5canundertakeindependentgamedevelopment.299-4CommonConceptsofProgrammingLanguages

Inthissection,weintroducesomebasicelementsandcommonconceptsinaprogramminglanguage.AlltheexamplesinthissectionarebasedonClanguage.

IdentifiersAnidentifierisusedtonameanobject.Identifiersallowustoreservememorylocationsthatcanbereferencedbytheidentifier’snameinourprogram.

DataType:

Adatatypedefinesasetofvaluesandthesetofoperationsonthosevalues.Forexample,inClanguage,therearefivebasicdatatypes:int,char,float,double,andvoid.Apartfromthesimpledatatypes,Clanguagealsodefinesarrays,pointers,structures,unions,andfunctions.

30

Variables:Variableisanamedmemorylocationassociatedwithanidentifier,whichcontainssomeknownorunknownstoredvalue,asshowninFigure9.5.Thevalueofvariablescanchangeduringruntime.

Variabledeclarations:Adeclarationisastatementthatassociatesatypeandname(identifier)withavariable,anaction,orsomeotherentitywithinthelanguagethatcanbegivenanamesothattheprogrammercanaccessthatitem,object,orprocessbyname.Mostprogramminglanguagesrequirethatvariablesmustbedeclaredpriortouse.Thecomputerallocatestherequiredstoragespaceandnamesit.

CommonConceptsofProgrammingLanguages 31CommonConceptsofProgrammingLanguages

Constants:

Aconstantisanamedmemorylocationwithanassociatedvalue,butthevaluecannotbealteredduringtheexecutionafterithasbeendefinedatthebeginningoftheprogram.ForexampleinCorC++program,πcanbedefinedatthebeginningandusedduringexecutionoftheprogram,suchas

constfloatpi=3.14;

Thetypeofconstantmustbedefinedwhenitisdeclared.

Figure9.5Variables32CommonConceptsofProgrammingLanguages

InputandOutput:

Inputisusedtoreaddatafromotherdevices(e.g.monitorandfile).Outputisusedtowritedatatootherdevices.Everylanguageusuallyprovidessomeinput/outputfunctionsorinterfaces.

Expressions:

Anexpressiondefinesasetofoperandsandoperators.Theseoperatorsincludearithmeticoperators,relationaloperatorsandlogicaloperators.Table9.7,Table9.8andTable9.9showssomeoperatorsusedinC,C++,andJava.

OperatorDefinitionExample+-*/%AdditionSubtractionMultiplicationDivision(theresultisthequotient)Division(theresultistheremainder)7+118-3a*2a/b20%3++--Increment(add1tothevalueofthevariable)Decrement(subtract1fromthevalueofthevariable)i++i--Table9.7Arithmeticoperators33CommonConceptsofProgrammingLanguages

Table9.8RelationaloperatorsOperatorDefinitionExample<

<=>

>===!=LessthanLessthanorequaltoGreaterthanGreaterthanorequaltoEqualtoNotequaltocount<6count<=6count>5count>=5a==(b+c)a!=bOperatorDefinitionExample!&&||NotAndOr!(a>b)(a<3)&&(b>6)(a<7)||(b>15)Table9.9Logicaloperators34CommonConceptsofProgrammingLanguages

Statements:

Astatementisacommandthatcausesaspecificactiontobeperformedbytheprogram.InClanguage,anexpressionbecomesastatementwhenitisfollowedbyasemicolon.Statementsareexecutedinsequenceanddonothavevalues.Theyaretranslateddirectlyintooneormoreexecutablecomputerinstructions.Figure9.6showsthecategoriesofthestatements.

Figure9.6Statements35CommonConceptsofProgrammingLanguages

Functions:

Functionisanindependentmodule

thatiscalledtodospecifictasks.Insomeprogramminglanguages,afunctionisequivalenttoasubroutine,oraprocedure.Forexample,afunctionissimilartoasubroutineorfunctioninFORTRAN,amethodormemberfunctioninmostobject-orientedlanguages,oraprocedureorfunctioninCandPascal.Afunctionprovidesaconvenientwaytoencapsulatesomecomputation,whichcanthenbeusedwithoutcaringaboutitsimplementation.Sometimes,knowingtheexecutionresultisenough.So,withproperlydesignedfunctions,itispossibletoignoretheexecutionprocessofajob.Figure9.7isanexampleoffunctiondeclaration.

36CommonConceptsofProgrammingLanguages

Figure9.7Functiondeclaration379-5NotoriousSoftwareErrors

Intheprogrammingprocess,youmustbethoughtfultoavoidvariousmistakes.Otherwise,thosemistakesmaycausedisastrousconsequences.Herearesomeexamplesofnotoriousbugswhichhavebadinfluenceatthattime.

Bug1:MarinerIspaceprobe(1962)

Whiletranscribingahandwrittenformulaintoacomputernavigationcode,asinglebarwasleftout.

Consequence:Thevesselwentsofaroffthemissioncontrolthatithadtobedestroyed.An$18.5millionspaceexplorationvehiclewaslost.Bug2:AT&Tnetworkoutage(1990)

AbuginanewreleaseofthesoftwarethatcontrolsAT&T's#4ESSlongdistanceswitchescausesthesemammothcomputerstocrash.

Consequence:Leavinganestimated60thousandpeoplewithoutlongdistanceserviceforninehours.AT&Tlostsome$60millionto$75million.38NotoriousSoftwareErrorsBug3:Pentiumchipsmathcoprocessorerror(1993)

Thebuilt-individerinthePentiumFPU(floatingpointunit)hadaflaweddivisiontable.

Consequence:Intel’sPentiumchipoccasionallymademistakesbeyondtheeighthdecimalpoint.Bug4:ExplosionoftheAriane5rocket(1996)

Theconversionofa64-bitfloatingpointtoa16bitsignedintegerwasfailedbecausethefloatingpointnumberwaslargerthan32,767,whichisthelargestintegerstorableina16bitsignedinteger.

Consequence:Therocketexplodedjust40secondsafterlift-offonitsmaidenvoyage.39NotoriousSoftwareErrorsBug5:Marsclimateorbitercrashes(1998)

Theuseofimperialunitsinsteadofmetricsystemintheorbiterbythesubcontractorcausesthisaccident.

Consequence:Thecrashofthe$125millionspacecraftonRedplanet.Bug6:MillenniumBugorY2K(1999)Twodigitswereusedtostoretheyearfordates,soyear2000couldonlyberepresentedas‘00’,whichmightconfusecomputersintomisinterpreting‘00’asyear1900ratherthan2000.

Consequence:ManydevicescontainingcomputerchipswerebelievedtobeatrisksopreparationsfortheY2Kbughadasignificantcostandtimeimpactonallindustries.40NotoriousSoftwareErrorsBug7:Software-relatedradiationtherapyfailure(2001)

AbugintheMultidatasoftwarecausedthepatientstobeover-radiatedandtheprocesswentonforsevenmonths.

Consequence:Cobalt-60machineinPanama'sNationalCancerInstituteoverdosedmorethantwo-dozenpatients

withgammaradiation,whichclaimedseverallives.Bug8:DisastrouspoweroutageinNortheasternAmericaandSoutheasternCanada(2003)Theoperatorturnedoffalarmcausedbyabugprovokedbythepowerflowmonitoringtool.

Consequence:PowerlinesweredeadinAmericaandtheinternationalconnectionsbetweenCanadaandtheUnitedStateswentofflineresultingin55millionpeoplewithoutpower.41NotoriousSoftwareErrorsBug9:MichiganDepartmentofCorrectionsgrantsprisonersearlyrelease(2005)

Theregisterincorrectlyreportedearlyreleaseof23prisonersduetoacomputerprogrammingglitch.

Consequence:Anundisclosednumberofinmateswerealsokeptinjailpasttheirreleasedates.Bug10:ShutdownoftheHartsfield-JacksonAtlantaInternationalAirport(2006)

Asoftwaremalfunctionfailedtoalertthesecurityscreenersthattheimageofasuspiciousdevicewasjustpartofaroutinetest.

Outcome:Theairportauthoritiesevacuatedthesecurityareafortwohourswhilesearchingforthesuspiciousdevice,causingmorethan120flightdelays,andforcingmanytravelerstowaitoutsidetheairport.42NotoriousSoftwareErrorsBug11:L.A.Airportflightsgrounded(2007)Duetoasinglepieceoffaultyembeddedsoftwareonanetworkcard,incorrectdatawassentoutontheU.S.CustomsandBorderprotectionnetwork.Consequence:Morethan17,000planesweregroundedforthedurationoftheoutage.Bug12:GoogleaccidentlyblockstheInternet(2021)OneofGoogle'sprogrammerswasaddingwebsitestothemalwareregistrywhenhe

accidentallyentered"/"insteadofafullURL.