Introduction to Computer Science in C# Release 1.0 Andrew N. Harrington and George K. Thiruvathukal 10-September-2016 16:59:25 CONTENTS 1 Context 1 1.1 MotivationforThisBook . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 1.2 ResourcesOnline . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 1.3 DownloadingandReadingOptions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 1.4 ComputerScience,Broadly . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 1.5 ChapterReviewQuestions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 2 C#DataandOperations 9 2.1 ASampleC#Program . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 2.2 Lab: Editing,Compiling,andRunningwithXamarinStudio . . . . . . . . . . . . . . . . . . . . . . 13 2.3 Arithmetic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21 2.4 VariablesandAssignment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 2.5 SyntaxTemplateTypography . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29 2.6 Strings,PartI . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30 2.7 WritingtotheConsole . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31 2.8 C#ProgramStructure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32 2.9 CombiningInputandOutput . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37 2.10 StringSpecialCases . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41 2.11 SubstitutionsinConsole.WriteLine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42 2.12 ValueTypesandConversions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45 2.13 LearningtoSolveProblems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50 2.14 Lab: DivisionSentences . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52 2.15 ChapterReviewQuestions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55 3 DefiningFunctionsofyourOwn 57 3.1 AFirstFunctionDefinition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57 3.2 MultipleFunctionDefinitions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59 3.3 FunctionParameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60 3.4 MultipleFunctionParameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63 3.5 ReturnedFunctionValues . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64 3.6 TwoRoles: WriterandConsumerofFunctions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67 3.7 LocalScope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 68 3.8 StaticVariables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69 3.9 NotusingReturnValues . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70 3.10 LibraryClasses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71 3.11 Tracebacks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75 3.12 StaticFunctionSummary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 78 3.13 ChapterReviewQuestions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 80 4 BasicStringOperations 83 4.1 StringIndexing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83 i 4.2 SomeInstanceMethodsandtheLengthProperty . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84 4.3 ACreativeProblemSolution. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87 4.4 Lab: StringOperations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89 4.5 ChapterReviewQuestions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 90 5 Decisions 91 5.1 ConditionsI . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91 5.2 SimpleifStatements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91 5.3 if-elseStatements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93 5.4 MoreConditionalExpressions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96 5.5 MultipleTestsandif-elseStatements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 99 5.6 If-statementPitfalls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 102 5.7 CompoundBooleanExpressions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 104 5.8 NestedifStatements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 106 5.9 ChapterReviewQuestions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 108 6 WhileLoops 113 6.1 While-Statements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113 6.2 While-StatementswithSequences . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 121 6.3 InteractivewhileLoops . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 128 6.4 Short-Circuiting&&and|| . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 132 6.5 WhileExamples . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 133 6.6 MoreStringMethods. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 137 6.7 UserInput: UI . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 140 6.8 GreatestCommonDivisor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 140 6.9 Do-WhileLoops . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 144 6.10 NumberGuessingGameLab . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 147 6.11 ChapterReviewQuestions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 151 7 ForeachLoops 153 7.1 foreachSyntax . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 153 7.2 foreachExamples . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 154 7.3 ChapterReviewQuestions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 155 8 ForLoops 157 8.1 For-StatementSyntax . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 157 8.2 ExamplesWithforStatements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 160 8.3 Lab: Loops . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 172 8.4 ChapterReviewQuestions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 174 9 Files,Paths,andDirectories 177 9.1 FilesAsStreams . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 177 9.2 WritingFiles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 177 9.3 ReadingFiles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 179 9.4 PathStrings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 183 9.5 DirectoryClass . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 185 9.6 FileClass . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 185 9.7 CommandLineExecution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 185 9.8 FIOHelperClass . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 187 9.9 ChapterReviewQuestions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 189 10 Arrays 191 10.1 OneDimensionalArrays . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 191 10.2 MusicalScalesandArrays . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 205 10.3 LinearSearching . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 208 ii 10.4 SortingAlgorithms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 209 10.5 BinarySearching . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 221 10.6 Lab: Arrays. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 223 10.7 Lab: Performance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 226 10.8 Multi-dimensionalArrays . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 230 10.9 ChapterReviewQuestions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 234 11 Lists 237 11.1 ListSyntax . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 237 11.2 .NetLibrary(API) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 240 11.3 ChapterReviewQuestions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 240 12 Dictionaries 243 12.1 DictionarySyntax . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 243 12.2 DictionaryEfficiency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 245 12.3 DictionaryExamples . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 245 12.4 Lab: FileDataandCollections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 247 12.5 ChapterReviewQuestions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 251 13 ClassesandObject-OrientedProgramming 253 13.1 AFirstExampleofClassInstances: Contact . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 253 13.2 ClassInstanceExamples . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 262 13.3 TheRationalClass . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 272 13.4 PlanningAClassStructure. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 281 13.5 ClassesAndStructs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 282 13.6 DefiningOperators(Optional) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 282 13.7 ChapterReviewQuestions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 285 14 Testing 287 14.1 Assertions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 287 14.2 Attributes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 287 14.3 TestingtheConstructor. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 288 14.4 TestingRationalComparisons . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 289 14.5 TestingRationalArithmetic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 289 14.6 TestingRationalConversions(toothertypes) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 290 14.7 TestingtheParsingFeature. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 291 14.8 RunningtheNUnitTests . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 291 15 Interfaces 295 15.1 RationalsRevisited . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 295 15.2 CsprojectRevisited . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 297 15.3 ChapterReviewQuestions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 301 16 Recursion 305 17 DataStructures 307 18 Appendix 309 18.1 DevelopmentTools . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 309 18.2 XamarinStudio. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 312 18.3 CommandLineIntroduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 313 18.4 PrecedenceofOperators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 317 18.5 Homework: GradeCalculation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 318 18.6 Homework: GradeCalculationfromIndividualScores . . . . . . . . . . . . . . . . . . . . . . . . . 322 18.7 Homework: GradeFile . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 324 iii 18.8 Homework: BookList . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 328 18.9 GroupProject. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 332 18.10 Lab: VersionControl . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 338 18.11 MercurialandTeamwork. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 349 18.12 Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 351 Bibliography 353 Index 355 iv CHAPTER ONE CONTEXT 1.1 Motivation for This Book Thisisreallyapreface,buttheotherwiseverycapableSphinxpublishingenvironmentthatweuseisnotsetupfora separatepreface. 1.1.1 Pedagogy Our first aim is to provide a good introduction and conceptual framework for more computer science, not an ency- clopediccoverageofC#. C#willnotbemoststudents’onlylanguage,ornecessarilythemostused. Designingand creatingalgorithmsinaparticularlanguageisanimportantskill,requiringongoingeffort,somostofthetextisstill centeredonC#. C#isanobject-orientedlanguage. Thereistheongoingargumentaboutwhentointroducedetailsofobject-oriented programming. WelasttaughtJava,objectsfirst. Studentsdutifullyfollowedourlead. Later,wesawquickprograms that students wanted to write for themselves, that were layered with totally unnecessary and distracting instances of objects. Wehaveseenlessproblemwiththeoppositeorder,whichweuse: startoffwithmoreproceduralprogramming,then introducetheuseofinstancesofexistingclassesofobjects,andthenmovetodesigningclasseswithinstancevariables, constructors,andinstancemethods,andseewheretheyaretrulyuseful. Ifyouprefer,afterthechapteronfunctions youcanreadthefirstcoupleofsectionsinClassesandObject-OrientedProgramming,thatcoverdefiningyourown simpleobjects. We tend to introduce examples first, and then the general syntax, and then more examples and exercises. Later examplesonasubjectaresometimesessentiallylinkstodocumentedcodethatisbothdirectlyvisibleontheweband intheseparatedownloadofalloftheexamplesourcecode. Therearereviewquestionsattheendofmostchapters. Thereviewquestionsmayseemtobeinastrangeorder:Often we invite students to consider a general overarching theme in an early question. In case that was too much to bite off,laterquestionsoftenexplicitlyaddressaspecificpointthatwouldhavebeenanimplicitpartofanearliergeneral question. Sometimesalatermorepointedquestionevengivesananswertopartofanearlierquestion. Labsareintendedasearlypracticeonasubject,withgenerallysmallbitsrequestedatatime.Theyareusuallyincluded in the main body of the book soon after the needed background is introduced. There are also larger assignments as someoftheappendixsections. 1.1.2 C# and Mono Wehavetaughtintroductoryprogrammingformanyyears,throughaprogressionofprogramminglanguages. Ourlast languagewasJava,stillthelanguageoftheAPtest,whichdrivessomanyintroductorytexts. 1 IntroductiontoComputerScienceinC#,Release1.0 WehadC#inmind: Itisamoremodernlanguage. ItsdesignersgottoreflectontheglitcheswithJava,andaddress themeffectively. ThekeyproblemwithC#usedtobethatitwastotallyaMicrosoftlanguageforWindows. Manyofourstudentshave theirown machines: manyare OS-Xmachines fromApple; someare Linux. We didnot wantto cutthose students off. NordidwewanttolimitstudentstothinkingofacomputerasaWindowsmachine. Meanwhiletheopensource implementationofC#,Mono,hasbeenmaturing,alongwithitstoolchains. While many open-source tools have hackers jumping in to eliminate bugs, and maybe providing enough documen- tation for a professional, documentation for a beginner is often lacking. This book contributes there, partly in the documentation for Mono’s lovely interactive environment csharp, and also for the integrated development environ- ment,XamarinStudio. WeshowbeginnershowtostartusingtheXamarinStudioenvironment,withitslargearrayof features(notallneededbythebeginner),andintroducemorefeaturesasneeded. We aim to end up with a book that provides a solid conceptual framework for beginning computer scientists in the context of the clean, well-established modern language, C#, using multi-platform free and open-source tools, with cleardocumentation. Wehopethatyoufindthistobeawinningcombination. 1.2 Resources Online ThisbookisdesignedforComp170atLoyolaUniversity,Chicago.Thematerialsareavailabletoallontheweb.Here aresomeimportantweblinks: • Thecourseexamplefile, istheessentialresourcetodownloadandunzipontoyourmachine. Thezipfileand thefolderitunzipstohavealongname,introcs-csharp-master-examples. Wesuggestyourenametheunzipped folderexamplestomatchlaterreferences. Computerprogramsaredesignedtorunonacomputerandsolveproblems. Thoughtheinitialproblemswillbe tinyandoftensilly,theywillserveaslearningtoolstoprepareforsubstantiveproblems. • http://introcs.cs.luc.edu is an online text version for your web browser. See also Downloading and Reading Optionsforpdfandepubversions. Exceptonverygeometricallyorientedtopics,text-orientedlearnersmaybe happiestjustreadingthebookinoneoftheseformats. • https://luc.box.com/CSharpVideosisabox.comfoldercontainingallthevideos. Thenumbersatthebeginning of the titles are chapter and section numbers from the text. These make it easy to sequence the videos, even thoughthereisnotanautomaticplaylist. Thelistinginbox.comtakesupseveralpages. Thesebox.comvideos maybe – streamed,includingatfullsize(thoughgenerallyafteraninitialdelay), – downloadedindividuallyor – thewholegigabytefoldercanbedownloadedatoncetoplaylateronyourmachine. (Thisisachoiceon themenuunderthepage’sFolderOptions.) Thereisamixtureofnewhigh-defvideosandolderlowerresolution800x600pixelvideos. Inthatfoldersee 00README.html, https://luc.box.com/s/2lqak4pbsdcyw08ds3ia, for a description of the differences between theoldvideosandthelatestupdateoftheonlinebook. For those who learn best with spoken words combined with written words, the videos should be a good start. Evenifyouuseavideoforasection,youareencouragedtoreviewthewrittentextafterward. Thenbeawareof thewrittenversionforquickreference. Thewrittentextmayincludeextradetailsandexercises,anditwillhave thelatestrevisions. Invariousformats,beawareofthesehelpfulfeatures: 2 Chapter1. Context IntroductiontoComputerScienceinC#,Release1.0 • We have picked out particularly important words, phrases, and symbols, and put them in our index, which is accessiblefromthebannerofeachwebpage. Thebannerstaysvisibleifthewindowisbigenough,andifthe windowissmaller,thebaneronlyappearsatthebeginningofthepagewithadropdownmenuformostofthe options. • Inawebversiononourwebsite,youcanusetheSearchoptiontolookforwords,ingeneral. Thesearchlinkis alsoaccessiblefromthewebpagebanner. Thisdoesnotworkonadownloadedlocalhtmlcopy. • The web version and pdf versions display mathematical formulas prettily. If you use the local html version whennotconnectedtotheinternet,youseeonlytheLaTexencodedsourceforformulas. Whileofflinereading sectionswithmathformulas,wesuggestusingthepdfversion. • We start with a brief table of contents for the whole book. In the web versions you can get the most detailed tableofcontentsforasinglechapterbyclickingonachaptertitleinthemaintableofcontentsorachaptertitle intheSitedrop-downmenuinthebanner. • Thewebversionshiftsthebehaviorofthetopbannerdependingonscreenresolution,soitadaptsforanything fromlargemonitorstosmallmobiledevices. Withawidescreenthebannerstaysatthetopofyourscreen,and showsallthestandardinternallinksanddrop-downmenus. Onanarrowerscreenthebannerisonlyatthetop ofeachwebpage,andscrollsoffthescreen; theonlydirectlinkistothemaintableofcontents,whiletherest ofthelinksofthewideversioncanbeaccessedviatheiconattherightsideofthebanner. Herearefurtherlinksthatmaybeusefulinourrepository: • https://github.com/LoyolaChicagoBooks/introcs-csharp/ is the home page for the repository of all the sources forthebook. Toreadthisbook,youdonotneedtogotothatURL,butifyoudo,thehomepagegivesyouan ideaofwhatupdateshavebeenmaderecentlytothebookoraccompanyingexamples. Sinceimprovementsare madeonanongoingbasis,thenotesaboutrecentchangesmaybeusefultoyou. ThemultipleproductionversionsaregeneratedlargelybySphinxsoftwarefromthecommonsetofsourcesin therepository. Thesourcesarelargelyplaintextfiles. • https://github.com/LoyolaChicagoBooks/introcs-csharp-examples/ is another repository containing the latest versions of the source code files. You can quickly browse and view individual files under the Source tab. Examplefilelinksthroughoutthistextrefertotheserepositoryfiles. 1.3 Downloading and Reading Options MostreaderswillwanttodownloadtheC#examplesinZIPformat. Moreexperiencedreaders(withpreviousback- ground)maypreferusingGitHub. () Table 1.1: ExampleSourceCodeandVideos Description URL C#Examples(asZIP) https://github.com/LoyolaChicagoBooks/introcs-csharp-examples/archive/master.zip Videos https://luc.box.com/CSharpVideos We offer the book in HTML, PDF, and EPUB formats. Kindle users should use EPUB, which can be converted to MOBIformat. (Weplantoofferitsoonthroughourmainsite.) 1.3. DownloadingandReadingOptions 3 IntroductiontoComputerScienceinC#,Release1.0 Table 1.2: AlternateBookFormats Format URL WebSite http://books.cs.luc.edu/introcs-csharp/ WebSite(offlineZIP) http://books.cs.luc.edu/introcs-csharp/download/html.zip PDF(USLetter) http://books.cs.luc.edu/introcs-csharp/download/comp170.pdf PDF(7x9Book) http://books.cs.luc.edu/introcs-csharp/download/comp170book.pdf EPUB(Experimental) http://books.cs.luc.edu/introcs-csharp/download/comp170.epub Warning: Thefollowingisfordevelopersonly! ThebooksourcecodeandexamplesareallmaintainedonGitHub. Wewelcomepullrequestsandwillacknowledge anyhelpfulandconstructivecontributions. Table 1.3: GitHub Description URL C#Examples https://github.com/LoyolaChicagoBooks/introcs-csharp-examples BookSource https://github.com/LoyolaChicagoBooks/introcs-csharp 1.4 Computer Science, Broadly We intend this book as an introduction to computer science, with a focus on creating problem solutions in the C# programming language. We should not jump in too quickly. You can get lost in our details and miss an idea of the muchlargerbreadthofcomputerscience. 1.4.1 Information Processing ComputerScienceisthestudyandpracticeofinformationprocessing. Thiscantakemanyforms. Manyformsappear inelectroniccomputers,butinformationprocessingtakesplaceinmanyothercontexts,too: Intheearlydaysofelectroniccomputers,theinformationwaslargelynumerical,calculatingmathematicalfunctions. Later analyzing textual information has become much more important, for instance: What can you tell about the severityofthecurrentfluoutbreakbyanalyzingthephrasinginGooglesearches? Imagesareanalyzed: Whatcanasatelliteimagetellyouaboutthedistributionofdrought? Sounds: howdoyouconvertverbalspeechaccuratelyintowrittensentences? DNAholdsinformationthatourbodiesprocessintoproteins. Our brain chemicals and electronic signals process information. There is rich interplay between cognitive scientists and computer scientists modeling problem solving in the brain with neural nets on a computer, sometimes to better understandbrainsandsometimestobettersolveproblemsonanelectroniccomputer. Economicsystemsarebecomingbetterunderstoodintermsoftheflowofinformation. Thecomputer doingcomputationsandprocessingcanbeafamiliarelectroniccomputer,butitcanbegenesorbrain chemicals,orawholesocietyasitseconomyadapts. 4 Chapter1. Context