Getting Into CS

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Getting into CS

Nowthatyouhavehadachancetoexperiencehowcomputersoperate,youaregoingtolearnsomespecificprogrammingconcepts.Theseinclude:

•  Variables•  Datatypes•  Loops•  CondiBonalstatements

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Data Types & Variables

Let’sstartwithashortdebriefofthesandwichacBvity:•  WeusedtheEnglishlanguagetocreateaseriesofinstrucBons

(theprogram)to‘acton’thematerialsor‘data’(e.g.,bread,jelly,andsoon)toproduceacertainoutputorresult(asandwich).

•  Incomputerscienceaprogramminglanguagehelpsaprogrammermakeacomputerdothings.TheprogramisasetofinstrucBonsthattellsacomputerwhattodowithcertaindataandhowtodoittoproduceacertainoutput.

•  Aprogramusuallycontainsdifferenttypesofdatatorepresentnumbers,leLersandsoon.Programsneedawayof‘remembering’thedatatheyaregiven;thisisusuallydonebycreaBngvariablesandpuOngdataintothem.

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Variables

Whatisavariable?• Imaginethatavariableisaboxthatcarriesacertainvalue.• Youcantakethevalueoutofthisvariable‘box’andputinanewone.• Youcanlookupthevalueintheboxanddothingswithit.• Youcantakethevaluesfromotherboxesandputtheminthisbox.

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Declaring Variables & Data Types

Inmostprogramminglanguages,youneedtodeclarevariablesbeforeyouusethem.

•  Meansthatyoumaketheboxesthatyouwanttostorevaluesin.

•  Justlikeinreallife,boxescomeinallshapesandsizes—andyouneedtherightboxfortheobjectyouaregoingtoputinit.•  Forexample:Youcannotfitabicycleintoajewelrybox,

right?•  Inprogrammingyouhavetohavetheright“size”boxfor

the“size”ofyourdata.•  Someboxescan'tstorecertainvaluesbeyondtheirlimits

(datatype).

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Activity

Let’slookbackatGe#ngtoKnowtheZRIDE.Howwouldyougo

aboutchangingthevalueofthevariablesinthistutorial?(Hint:Youassignitadifferentvalue!)

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Answer

voidloop(){Y=1.5;setPos(0,Y,0);return;}Becomesvoidloop(){Y=2.5;setPos(0,Y,0);return;}

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More on Data Types

•  InmathemaBcs,therearevariouswaysofrepresenBngnumbersandotherdata:•  differenttypesofnumbers(e.g.,wholenumbersanddecimals,posiBveandnegaBvenumbers)

•  setsofdatalikecoordinatepointsandvectors•  Inprogramming,anypieceofdatausedmustbe‘declared’to

tellthecomputertostoreanduseit.•  Ifyoudon’ttypeinadeclaraBonofyourdatapriortousingit,yourcomputerwilloutputanerror.

•  AlldeclaraBonsusethefollowingstructure: DataTypeName;

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More on Data Types: Example

Example:floatdistance;• ThisdeclaraBon,istellingthecomputerthetypeofdataitwillprocess—somethingknownasa‘floatnumber’—andthenameofthedatathatwillbeprocessed—inthiscase,datameasuringadistance.• InthesandwichacBvity,thedataisthematerials(peanutbuLer,jelly,andbread),andtheinstrucBonstellingtheperformerwhattodowiththe‘data’consBtutesthe‘program’.

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More on Variables

•  Remembertheanalogyaboutboxes?Well,whenyouarewriBngacomputerprogram,youoeenwanttheprogramtobeableto“remember”avalue.Youcandothisbyassigningtheimportantvaluetoanamedvariable.

•  Eachvariablehasanameandcontainsavalue.Forexample,avariablecanbenamedXandcontainthevalue2.ThusyoucansayX+Xequals4.Variablesarecategorizedbythetypesofdatatheystore.YoumusttellthecomputerwhattypeofdatayouwillbepuOnginthevariable.ALempBngtoputdataofthewrongtypeintoavariablewillcauseanerror.

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Activity Introducing Loops

InthelastacAvity,youwereaskedtowriteinstrucAonstomakeONEsandwich.HowwouldyouwriteinstrucAonsformaking

hundredsofsandwiches,forexample,inacafeteria?(Tomakethingssimpler,youcanassumeyouhaveunlimited

suppliesofthematerials!)

Let’sstartbylookingatthefinalinstrucAonsformakingsandwichesagain.

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Review Final Instructions for PBJ Sandwich

a)  Takeasliceofbreadb)  OpenthejarofpeanutbuLerbytwisBngthelidcounter

clockwisec)  Pickupaknifebythehandled)  InserttheknifeintothejarofpeanutbuLere)  PulltheknifeoutofthejarofpeanutbuLerandrunitacross

thesliceofbreadf)  Takeasecondsliceofbreadg)  Repeatstepsa–ewiththesecondslideofbreadandthejarof

jellyh)  Pressthetwoslicesofbreadtogethersuchthatthepeanut

buLerandjellymeet

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Activity Introducing Loops, continued

CanyouthinkofoneaddiAonalinstrucAonyoucanaddtotheseinstrucAonstotellthe‘performer’oracomputerhowtomake

100sandwiches?

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Example Answer to Activity Introducing Loops

a)  Takeasliceofbreadb)  OpenthejarofpeanutbuLerbytwisBngthelidcounter

clockwisec)  Pickupaknifebythehandled)  InserttheknifeintothejarofpeanutbuLere)  PulltheknifeoutofthejarofpeanutbuLerandrunit

acrossthesliceofbreadf)  Takeasecondsliceofbreadg)  Repeatstepsa–ewiththesecondslideofbreadandthejar

ofjellyh)  Pressthetwoslicesofbreadtogethersuchthatthepeanut

buLerandjellymeeti)  RepeatStepsa-h99more=mes

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Activity Introducing Conditionals

SupposethecafeteriaservesPB&Jsandwicheseverydayexcept

onFridays,whenitservesbothsandwichesandpizza.

Sincemoststudentswouldrathereatpizza,thecafeteriashouldmakefewersandwichesonFriday.

Howcouldyouchangeyourprogramtomakefewersandwiches

onlyonFridays?

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Example Answer to Activity Introducing Conditionals

a)  Takeasliceofbreadb)  OpenthejarofpeanutbuLerbytwisBngthelidcounter

clockwisec)  Pickupaknifebythehandled)  InserttheknifeintothejarofpeanutbuLere)  PulltheknifeoutofthejarofpeanutbuLerandrunit

acrossthesliceofbreadf)  Takeasecondsliceofbreadg)  Repeatstepsa–ewiththesecondslideofbreadandthejar

ofjellyh)  Pressthetwoslicesofbreadtogethersuchthatthepeanut

buLerandjellymeeti)  RepeatStepsa-h99more=mesunlesstodayisFriday

IftodayisFriday,repeatstepsa-h29more=mes