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[Powered by Google Translate] [Ġimgħa 4]

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[David J. Malan] [Università ta 'Harvard]

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[Dan huwa CS50.] [CS50.TV]

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>> Kull dritt, dan huwa CS50, u dan huwa l-bidu tal-ġimgħa 4,

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u dan huwa wieħed mill-algoritmi issortjar iżgħar rata possibbli.

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Liema wieħed ma kien li aħna biss jaraw hemmhekk?

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Dan kien it-tip bużżieqa, sabiex big O (n ^ 2) + somma,

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u fil-fatt aħna l-uniċi f'din id-dinja li jidhru li jafu

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liema tip bużżieqa huwa jew running time tiegħu.

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Tabilħaqq, dan kien intervista ma Eric Schmidt tal-Google

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u eks senatur Barack Obama biss ftit snin ilu.

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>> Issa, Senatur, int hawn fuq Google,

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u Inħobb naħseb tal-presidenza bħala intervista tax-xogħol.

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Issa, huwa diffiċli li jsibu xogħol bħala president, u int ser permezz tal-ħruxija issa.

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Huwa wkoll diffiċli li jsibu xogħol fil-Google.

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Aħna mistoqsijiet, u aħna jistaqsu mistoqsijiet lill-kandidati tagħna,

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u dan huwa wieħed mill Larry Schwimmer.

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You guys think jien kidding? Huwa dritt hawn.

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X'inhi l-aktar mod effiċjenti biex issolvi xi miljun 32-bit interi?

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[Daħk]

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Well-

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Jien sorry. >> No, no, no, no.

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Naħseb li l-tip bużżieqa tkun l-mod żbaljat biex imorru.

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>> Come on, li qallu dan?

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Last week lura aħna ħa pawża mill-kodiċi, għall-inqas għal ġurnata,

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u beda jiffoka fuq xi ideat ta 'livell ogħla u soluzzjoni ta' problemi b'mod aktar ġenerali

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fil-kuntest ta 'tiftix u għażla,

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u aħna introdotti xi ħaġa li aħna ma SLAP dan l-isem fuq il-ġimgħa li għaddiet,

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iżda notazzjoni asintotiku, il-Big O, il-Omega Big,

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u xi kultant l-notazzjoni Theta Big, u dawn kienu sempliċiment modi

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jiġu deskritti l-running time ta 'algoritmi,

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kemm ħin li jieħu għall algoritmu jiddekorri.

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>> U inti tista 'recall li inti tkellem dwar il-ħin qed taħdem f'termini tad-daqs

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ta 'l-input, li aħna ġeneralment sejħa n, ikun x'ikun il-problema jista' jkun,

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fejn n huwa n-numru ta 'nies fil-kamra,

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in-numru ta 'paġni fil-ktieb tat-telefon, u bdejna biex jikteb affarijiet out

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bħall O (n ^ 2) jew O (n) jew O (n log n),

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u anke meta l-matematika ma pjuttost xogħol barra hekk perfettament

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u kien n ² - n / 2 jew xi ħaġa bħal dik

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aħna minflok sempliċiment tarmi l bogħod xi wħud mit-termini ordni aktar baxxi,

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u l-motivazzjoni hemm li aħna verament jixtiequ

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tip ta 'triq għan li jevalwa

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il-prestazzjoni tal-programmi jew il-prestazzjoni ta 'algoritmi

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li fl-aħħar tal-ġurnata m'għandha x'taqsam xejn ma ', pereżempju,

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bil-veloċità ta 'kompjuter tiegħek illum.

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>> Per eżempju, jekk inti jimplimentaw sort bużżieqa,

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jew inti jimplimentaw jingħaqdu tip jew l-għażla it-tip fuq il-kompjuter tal-lum,

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kompjuter GHz 2, u inti run,

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u li tieħu xi numru ta 'sekondi, sena d-dieħla hemm GHz 3

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jew kompjuter frekwenzi 4 GHz, u inti tista 'imbagħad isostni li "Ara naqra, algoritmu tiegħi

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issa huwa darbtejn malajr, "meta fir-realtà dan huwa ovvjament mhux il-każ.

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Huwa biss il-hardware gotten aktar malajr, imma kompjuter tiegħek

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ma, u hekk aħna verament irridu li armih affarijiet simili

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multipli ta '2 jew multipli ta' 3 meta niġu biex tiddeskrivi

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kif fast jew bil-mod kif algoriżmu huwa u verament biss jiffoka

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fuq n jew xi fattur tiegħu,

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xi setgħa tiegħu bħal fil-każ tal-tipi mill-aħħar ġimgħa.

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U tfakkar li bl-għajnuna ta 'tip jingħaqdu

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konna kapaċi li jagħmlu dan ħafna aħjar minn tip bużżieqa u sort l-għażla

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u sort inserzjoni anke.

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>> Sirna sa n log n, u għal darb'oħra,

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ifakkar li log n ġeneralment tirreferi għal xi ħaġa li tikber

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aktar bil-mod imbagħad n, sabiex n log n s'issa kienet tajba

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għaliex kien inqas minn ² n.

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Iżda biex jiksbu n log n ma sort jingħaqdu

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dak li kien il-raħs bażiku ta 'idea li kellna biex jinfluwenzaw

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li aħna wkoll influwenzati lura fil-ġimgħa 0?

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Kif aħna ma tindirizza l-problema issortjar cleverly bil sort jingħaqdu?

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Liema kienet l-għarfien ewlieni, forsi?

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Kulħadd fil-livelli kollha.

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Okay, ejja jieħu pass lura.

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Iddeskrivi jingħaqdu sort fi kliem tiegħek.

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Kif ma taħdem?

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Okay, aħna ser ringiela lura għal 0 ġimgħa.

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Okay, yeah.

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[Inaudible-istudent]

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Okay, tajba, hekk aħna maqsuma l-firxa ta 'numri fil 2 biċċiet.

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Aħna magħżula kull waħda minn dawk il-biċċiet, u allura aħna magħquda magħhom,

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u Rajna din l-idea qabel ta 'teħid problema li l-din big

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u tqattiegħ it up fis-problema li l-din kbar jew dan kbar.

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>> Recall-eżempju ktieb tat-telefon.

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Recall-algoritmu awto-għadd minn ġimgħat ilu,

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sort hekk jingħaqdu ġie sintetizzat minn din pseudocode hawn.

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Meta inti qed tingħata l-elementi n, l-ewwel kien sanità check.

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Jekk n <2 allura ma tagħmel xejn fil-livelli kollha

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għaliex jekk n <2 allura n hija ovvjament 0 jew 1,

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u hekk jekk huwa jew 0 jew 1 hemm xejn biex issolvi.

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Inti qed isir.

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Lista tiegħek huwa diġà trivially magħżula.

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Imma inkella jekk inti stajt ltqajna 2 jew aktar elementi jimxi 'l quddiem u jaqsmuhom

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fis-2 nofsijiet, tax-xellug u tal-lemin.

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Sort kull wieħed minn dawk nofsijiet, u mbagħad jingħaqdu l nofsijiet magħżula.

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Iżda l-problema hawn hija li ewwel daqqa t'għajn dan iħoss simili aħna qed punting.

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Din hija definizzjoni ċirkulari li jekk stajt talab li inti sort dawn l-elementi n

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u int javżak me "Kull dritt, multa, aħna ser sort dawk l-elementi n / 2 u dawk n / 2,"

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imbagħad mistoqsija li jmiss tiegħi se tkun "Multa, kif taħseb sort l-n / 2 elementi?"

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>> Iżda minħabba l-istruttura ta 'dan il-programm,

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minħabba li hemm din il-bażi, biex ngħidu hekk,

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F'dan il-każ speċjali li tgħid jekk n huwa <xi valur fiss bħal 2-ritorn immedjatament.

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Ma jirrispondu mal din ir-risposta ċirkolari istess.

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Dan il-proċess, dan ċikli eventwalment se jispiċċaw.

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Jekk Nitlobkom "Sort dawn l-elementi n," u inti tgħidli, "Fine, sort dawn n / 2,"

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imbagħad inti tgħidli, "Fine, sort dawn n / 4, n / 8, n/16,"

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eventwalment inti ser jaqsam minn numru kbir biżżejjed

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li inti ser ikollok xellug element biss 1, f'liema punt inti tista 'tgħid,

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"Hawnhekk, hawn huwa element wieħed magħżula."

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Imbagħad il-brilliance ta 'dan algoritmu sa hawnhekk huwa li ġejjin mill-fatt

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li ladarba inti għandek kollha ta 'dawn il-listi individwalment magħżula,

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li kollha huma ta 'daqs 1, li jidher li jkun inutli,

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ladarba tibda qed jingħaqdu magħhom u l-amalgamazzjoni tagħhom

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inti jibnu finalment kif Rob għamlet fil-video lista finalment magħżula.

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>> Iżda din l-idea testendi lil hinn issortjar.

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Hemm din l-idea inkorporat f'dan il-programm magħruf bħala recursion,

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l-idea li biha inti programm,

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u biex isolvu xi problema inti sejħa lilek innifsek,

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jew imqegħda fil-kuntest tal-ipprogrammar ta 'lingwi inti funzjoni,

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u sabiex issolvi problema, inti l-funzjoni sejħa lilek innifsek

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ġdid u għal darb'oħra u għal darb'oħra, imma int l-funzjoni

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ma jistgħux jikkontestaw lilek innifsek drabi infinitament ħafna.

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Eventwalment inti għandek qiegħ barra, biex ngħidu hekk,

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u għandek xi kundizzjoni bażi hard-kodifikati li tgħid

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f'dan il-punt niefqu milli nsejħulha ruħek sabiex il-proċess kollu

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finalment ma fil-fatt jieqfu.

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Xi jfisser dan verament tfisser, għall recurse?

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>> Ejja naraw jekk nistgħu nagħmlu sempliċi, eżempju wieħed trivjali ma ', ngħidu aħna,

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3 persuni me up hawn fuq il-palk, jekk xi ħadd ikun komdu.

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1, come fuq up, 2 u 3.

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Jekk inti tixtieq li toħroġ 3 up here.

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Jekk inti tixtieq li toqgħod dritt li jmiss lili hawn fil-linja, ejja ngħidu li l-problema in kwistjoni

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huwa ferm trivially jgħodd in-numru ta 'nies li huma hawnhekk.

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Iżda franchement, jien għajjien ta 'dawn eżempji għadd.

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Dan ser jieħu xi żmien, 1, 2, u dot, dot, dot.

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Huwa ser jieħu dejjem.

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I d pjuttost biss Punt din il-problema għal kollox bl-għajnuna ta 'liema l-isem tiegħek?

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Sara. >> Sara, id-dritt.

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Kelly. >> Kelly u?

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>> Willy. >> Willy, Sara, Kelly, u Willy.

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Dritt issa I ġew staqsa l-mistoqsija minn xi ħadd

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kif ħafna nies huma fuq dan l-istadju, u għandi l-ebda idea.

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Din hija lista verament twila, u għalhekk minflok jien ser jagħmlu dan trick.

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Jien ser titlob lill-persuna li jmiss lili biex jagħmlu ħafna mix-xogħol,

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u ladarba hi qed isir tagħmel ħafna mix-xogħol

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Jien ser jagħmlu l-inqas ammont ta 'xogħol possibbli u biss żid 1

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għal dak kollu tweġiba tagħha huwa, so here we go.

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Stajt ġew mitluba kif ħafna nies huma fuq il-palk.

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Kif ħafna nies huma fuq il-palk lejn ix-xellug tal inti?

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Ix-xellug ta 'lili? >> Okay, iżda ma iqarrqu.

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Li tajjeb, li l-korretta, imma jekk irridu li tkompli din il-loġika

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ejja nassumu li inti simili trid Punt din il-problema fuq ix-xellug tal inti,

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hekk minflok tweġiba direttament jimxi 'l quddiem u biss jgħaddu l-Buck.

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Oh, kif ħafna nies huma fuq ix-xellug ta 'lili?

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Kif ħafna nies huma fuq ix-xellug?

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1.

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[Daħk]

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Okay, hekk 0, iva, liema issa Willy għamlet

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huwa inti ħadthom lura tweġiba tiegħek f'din id-direzzjoni qal 0.

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Issa, x'għandek tagħmel? >> 1.

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Okay, hekk int l-1, sabiex inti tgħid, "Kull dritt, jien ser żid 1

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għal dak kollu għadd Willy kien, "sabiex 1 + 0.

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Inti issa 1 sabiex it-tweġiba tiegħek għall-dritt huwa issa '

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1. >> U minjiera tkun 2.

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Tajjeb, hekk int tieħu l-risposta preċedenti tal-1,

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żżid l-ammont minimu ta 'xogħol li inti trid tagħmel, li huwa 1.

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Inti issa għandhom 2, u inti mbagħad idejn lili li valur?

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3, I mean, sorry, 2.

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Tajba.

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>> Well, kellna 0 ix-xellug.

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Imbagħad kellna 1, u allura aħna żid 2,

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u issa int għoti me-numru 2,

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u hekk jien tgħid, okay, 1, 3.

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Hemm tabilħaqq 3 min-nies bil-wieqfa li jmiss lili fuq dan l-istadju,

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hekk aħna seta ovvjament għamlu dan ħafna linearment,

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ħafna fil-moda ovvju, imma dak ma aħna verament do?

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Aħna ħa problema ta 'daqs 3 inizjalment.

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Aħna mbagħad kissru l-isfel fis-problema ta 'daqs 2,

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imbagħad problema ta 'daqs 1, u mbagħad finalment l-każ bażi

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Kien verament, oh, hemm ebda waħda hemm,

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f'liema punt Willy lura effettiv risposta hard-kodifikati koppja ta 'drabi,

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u t-tieni waħda kienet imbagħad effervexxentement up, effervexxentement up, effervexxentement up,

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u mbagħad billi żżid f'dan 1 1 addizzjonali

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konna implimentati din l-idea bażika ta 'recursion.

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>> Issa, f'dan il-każ hija ma verament issolvi problema

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kwalunkwe aktar effettiv allura Rajna s'issa.

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Imma naħseb dwar l-algoritmi li aħna ghamilt fuq il-palk s'issa.

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Kellna 8 biċċiet tal-karti fuq il-chalkboard,

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fuq video meta Sean kienet qed tfittex għall-numru 7, u dak li ma hu verament do?

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Ukoll, huwa ma jagħmel ebda tip ta 'qasma u conquer.

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Hu ma tagħmel xi tip ta 'recursion.

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Pjuttost hu biss ma dan algoritmu lineari.

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Imma meta aħna introduċiet l-idea ta 'numri magħżula fuq il-palk jgħixu ġimgħa li għaddiet

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allura kellna din istint ta 'ser-nofs,

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f'liema punt kellna lista iżgħar ta 'daqs 4 jew lista oħra ta' daqs 4,

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u allura kellna l-istess problema eżatt, hekk aħna ripetut, ripetuta, ripetuta.

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Fi kliem ieħor, aħna recursed.

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Grazzi ħafna għal 3 voluntiera tagħna hawn biex juru recursion magħna.

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>> Ejja naraw jekk aħna ma tistax tagħmel dan issa konkret ftit aktar,

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isolvi problema li għal darb'oħra stajna nagħmlu pjuttost faċilment,

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iżda aħna ser jużawha bħala pass lejn implimentazzjoni ta 'dan l-idea bażika.

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Jekk irrid biex tiġi kkalkulata l-għadd totali tal-mazz ta 'numri,

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per eżempju, jekk inti tgħaddi fin-numru 3,

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Irrid li jtik l-valur tal sigma 3,

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hekk is-somma ta 3 + 2 + 1 + 0.

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Irrid li terġa 'lura l-risposta 6,

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hekk aħna ser timplimenta din il-funzjoni sigma, din il-funzjoni kalkolu totali

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li, għal darb'oħra, jieħu fil-input, u mbagħad jirritorna l-għadd totali

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ta 'dak in-numru it-triq kollha sa 0.

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Nistgħu nagħmlu dan pretty sempliċi, id-dritt?

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Stajna nagħmlu dan ma 'xi tip ta' struttura looping,

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so let me imorru quddiem u tikseb dan beda.

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>> Inkludi stdio.h.

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Let me nikseb myself fis ewlenija biex jaħdmu ma 'hawn.

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Ejja tiffranka dan bħala sigma.c.

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Imbagħad jien se jmorru fil hawn, u jien ser tiddikjara n int,

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u jien ser tagħmel dan li ġej waqt li l-utent ma jikkooperax.

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Filwaqt li l-utent ma jkunx tani numru pożittiv

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let me imorru quddiem u twassalhom għal n = GetInt,

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u let me tagħtihom xi struzzjonijiet dwar x'għandek tagħmel,

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hekk printf ("numru sħiħ pożittiv jekk jogħġbok").

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Just xi ħaġa relattivament sempliċi bħal dan hekk li mill-ħin aħna hit-linja 14

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issa għandna numru sħiħ pożittiv preżumibbilment n.

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>> Issa ejja nagħmlu xi ħaġa magħha.

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Let me imorru quddiem u kkalkulata l-kalkolu totali, hekk int somma = sigma (n).

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Sigma huwa biss kalkolu totali, hekk jien biss bil-miktub fil-mod fancier.

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Aħna ser biss sejħa hija sigma hemmhekk.

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Dik hija s-somma, u issa jien ser jistampa r-riżultat,

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printf ("Is-somma hija% d \ n", somma).

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U allura jien ser jirritorna 0 għal miżura tajba.

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Aħna ghamilt dak kollu li dan il-programm tirrikjedi ħlief il-parti interessanti,

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li huwa li fil-fatt jimplimentaw il-funzjoni sigma.

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>> Let me jinżlu hawn sal-qiegħ, u let me tiddikjara funzjoni sigma.

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Huwa ltqajna biex jieħdu varjabbli li ta 'numru sħiħ tip,

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u liema tip ta 'data ma nixtieq li jirritornaw preżumibbilment minn sigma?

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Int, minħabba I tixtieq li jilħqu l-aspettattivi tiegħi fuq il-linja 15.

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Fil hawn let me go l quddiem u jimplimentaw din

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b'mod pjuttost sempliċi.

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>> Ejja imorru quddiem u jgħidu somma int = 0,

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u issa jien se jmorru jkollhom ftit loop hawn

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li għaddej biex ngħid xi ħaġa bħal din,

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għal (i int = 0; I <= in-numru; i + +) somma + = i.

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U mbagħad jien ser jirritorna somma.

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I jistgħu jkunu implimentaw din fi kwalunkwe numru ta 'modi.

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I setgħet tuża loop waqt.

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I setgħet tinqabeż jużaw il-varjabbli somma jekk jien verament riedu,

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iżda fil-qosor, aħna biss għandhom funzjoni li jekk jien ma goof tiddikjara somma hija 0.

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Imbagħad ttenni minn 0 fil sa permezz-numru,

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u fuq kull iterazzjoni hija żżid li l-valur attwali biex somma u mbagħad jirritornaha somma.

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>> Issa, hemm ottimizzazzjoni żgħir hawn.

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Din hija probabbilment pass moħlija, iżda dan ikun hekk. Dik il-multa għal issa.

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Aħna l-inqas tkun bir-reqqa u jmorru 0 it-triq kollha fuq up.

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Mhux iebsa ħafna u pjuttost sempliċi,

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iżda jirriżulta li l-funzjoni sigma għandna l-istess opportunità

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kif għamilna hawn fuq il-palk.

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Fuq il-palk aħna biss magħduda kif ħafna nies kienu jmiss lili,

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iżda minflok jekk ridna li jgħodd in-numru 3 + 2 + 1

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fuq l isfel għal 0 nistgħu simili Punt għal funzjoni

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li jien ser minflok tiddeskrivi bħala rikursivi.

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Hawn ejja do a sanità malajr jivverifika u kun żgur I ma goof.

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>> Naf li hemm mill-inqas ħaġa waħda f'dan il-programm li jien ma do wrong.

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Meta I hit jidħol jien se tikseb kull tip ta 'yelling fil lili?

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What am I se jkunu għajjat ​​fil dwar?

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Yeah, I nesa l-prototip, hekk jien jużaw funzjoni msejħa sigma fuq il-linja 15,

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iżda mhux dikjarat sat linja 22, so I aħjar b'mod proattiv go up here

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u tiddikjara prototip, u jien ser ngħid int sigma (int numru), u li hu.

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Huwa implimentati fil-qiegħ.

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>> Jew mod ieħor I tista 'ssolvi din il-

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I jistgħu jimxu l-funzjoni up hemm, li mhix ħażina,

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iżda mill-inqas meta programmi tiegħek tibda tikseb twil, franchement,

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Naħseb li hemm xi valur fil dejjem wara prinċipali fil-quċċata

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b'tali mod li inti fil-qarrej jista 'tiftaħ il-fajl u mbagħad minnufih tara

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dak il-programm qed tagħmel mingħajr ma jkollhom tfittxija permezz ta 'dan

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tfittex għal dik il-funzjoni prinċipali.

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Ejja jinżlu għal tieqa terminal tiegħi hawnhekk, jippruvaw jagħmlu sigma jagħmlu sigma,

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u I invitat up hawnhekk ukoll.

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Dikjarazzjoni impliċita ta GetInt funzjoni ifisser li stajt insejt biex jagħmlu x'iktar?

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[Inaudible-istudent]

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Tajba, hekk apparentement żball komuni, hekk ejja tpoġġi dan up hawn,

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cs50.h, u issa ejja mur lura għall-tieqa terminal tiegħi.

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>> I ser ċar l-iskrin, u jien ser terġa 'ssir jagħmlu sigma.

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Jidher li ikkumpilata. Let me issa run sigma.

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I ser tip fil-numru 3, u jien ma nikseb 6, u għalhekk mhux kontroll rigoruża,

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iżda mill-inqas jidher li tkun qed taħdem ewwel daqqa t'għajn, iżda issa ejja RIP l barra,

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u ejja fatt jwieżen l-idea ta 'recursion, għal darb'oħra,

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f'kuntest sempliċi ħafna sabiex fil-ħin ftit ġimgħat "

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meta aħna tibda tesplora l-istrutturi tad-data fancier minn matriċi

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għandna ieħor għodda fil-toolkit li biex

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jimmanipulaw dawk l-istrutturi tad-data kif Ser naraw.

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Dan huwa l-approċċ iterattiv, l-approċċ loop-based.

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>> Let me minflok issa jagħmlu dan.

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Let me minflok jgħidu li l-kalkolu totali ta 'numru

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fuq l isfel għal 0 huwa verament l-istess ħaġa bħat

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Numru + sigma (numru - 1).

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Fi kliem ieħor, l-istess bħal fuq l-istadju I punted lil kull wieħed mill-persuni li jmiss lili,

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u huma mbagħad miżmuma punting sakemm aħna finalment qiegħ barra fil Willy,

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li kellhom jirritornaw risposta hard-kodifikati like 0.

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Hawnhekk Issa aħna qed simili punting li sigma

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l-istess funzjoni kif kien oriġinarjament imsejjaħ, iżda l-għarfien ċavetta hawn

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hija li aħna mhux qed titlob sigma identiku.

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Aħna ma tgħaddi fis n.

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Aħna ċar li tgħaddi fin-numru - 1,

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hekk problema kemmxejn iżgħar, il-problema kemmxejn iżgħar.

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>> Sfortunatament, dan mhux pjuttost soluzzjoni għadhom, u qabel we tiffissa

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dak li jista 'jaqbeż kif ovvji f'xi minnkom

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let me imorru quddiem u terġa 'ssir jagħmlu.

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Jidher li jikkompilaw okay.

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Let me terġa 'ssir sigma mal 6.

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Whoops, let me terġa 'ssir sigma mal 6.

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Imxejna rajt dan qabel, għalkemm iż-żmien aċċidentalment aħħar ukoll.

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Għaliex ma I nikseb dan tort segmentazzjoni cryptic? Yeah.

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[Inaudible-istudent]

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M'hemm l-ebda każ ta 'bażi, u b'mod aktar speċifiku, dak li probabbilment ġara?

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Dan huwa sintomu ta 'liema komportament?

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Jgħidu li ftit louder.

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[Inaudible-istudent]

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Huwa ta 'loop infinita b'mod effettiv, u l-problema ma' linji infinita

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meta dawn jinvolvu recursion f'dan il-każ, funzjoni li ssejjaħ lilha nnifisha,

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dak li jiġri kull darba li inti sejħa funzjoni?

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Ukoll, think lura għal kif aħna stabbiliti l-memorja fil-kompjuter.

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Aħna qal li hemm dan blokki ta 'memorja imsejjaħ il-munzell li l-fil-qiegħ,

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u kull darba li inti sejħa funzjoni ta 'memorja ftit aktar gets mqiegħda

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fuq din il-munzell hekk imsejħa fih varjabbli lokali li funzjoni jew l-parametri,

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hekk jekk sigma sejħiet sejħiet sigma sigma jitlob sigma

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 jitlob sigma fejn ma dan il-għan l-istorja?

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>> Ukoll, huwa eventwalment żejda l-ammont totali

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ta 'memorja li inti għandek disponibbli għall-kompjuter tiegħek.

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Inti qbiż-segment li int suppost li toqgħod fi,

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u ikollok dan tort segmentazzjoni, qalba iddampjati,

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u liema qalba dumped ifisser huwa li jien issa jkollhom fajl imsejjaħ qalba

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li huwa fajl li jkun fih żero u dawk

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li attwalment fil-futur se tkun diagnostically utli.

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Jekk mhuwiex ovvju li inti fejn bug tiegħek

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inti tista 'attwalment tagħmel daqsxejn ta' analiżi forensika, biex ngħidu hekk,

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dwar dan il-fajl dump qalba, li, għal darb'oħra, huwa biss mazz sħiħ ta 'żero u dawk

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li essenzjalment jirrappreżenta l-istat tal-programm tiegħek fil-memorja

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il-mument li ġġarraf b'dan il-mod.

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>> Il-jiffissaw hawnhekk hija li ma nistgħux biss bl-addoċċ jirritorna sigma,

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in-numru + sigma ta 'problema kemmxejn iżgħar.

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Għandna bżonn li jkollhom xi tip ta 'każ bażi hawnhekk,

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u dak li għandu l-każ bażiku probabbilment tkun?

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[Inaudible-istudent]

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Okay, sakemm in-numru huwa pożittiv għandna attwalment jirritorna din,

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jew fi kliem ieħor, huwa n-numru jekk, ngħidu aħna, <= għal 0

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inti taf liema, jien ser imorru quddiem u lura 0,

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ferm simili Willy ma, u inkella, jien ser jimxi 'l quddiem

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u rritorna din, dan mhuwiex li ħafna iqsar

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mill-verżjoni iterattiv li aħna bit-tarjola up ewwel użu ta 'għall-loop,

346
00:18:44,000 --> 00:18:48,000
imma avviż li hemm din it-tip ta 'eleganti lilha.

347
00:18:48,000 --> 00:18:51,000
Minflok jirritornaw xi numru u jwettqu dan kollu matematika

348
00:18:51,000 --> 00:18:54,000
u żżid affarijiet up ma 'varjabbli lokali

349
00:18:54,000 --> 00:18:57,000
int minflok qal "Okay, jekk din hija problema faċli super,

350
00:18:57,000 --> 00:19:01,000
bħall-numru huwa <0, let me immedjatament jirritorna 0. "

351
00:19:01,000 --> 00:19:03,000
>> Aħna mhux se jolqot numri ta 'sostenn negattivi,

352
00:19:03,000 --> 00:19:05,000
hekk jien ser code hard-valur ta '0.

353
00:19:05,000 --> 00:19:08,000
Iżda mod ieħor, biex jimplimentaw din l-idea ta 'ġabra fil-qosor

354
00:19:08,000 --> 00:19:11,000
kollha ta 'dawn in-numri flimkien inti tista' effettivament tieħu gidma żgħir

355
00:19:11,000 --> 00:19:14,000
barra mill-problema, ħafna bħal għamilna hawn fuq il-palk,

356
00:19:14,000 --> 00:19:18,000
allura Punt il-bqija tal-problema lill-persuna li jmiss,

357
00:19:18,000 --> 00:19:20,000
imma f'dan il-każ il-persuna li jmiss huwa lilek innifsek.

358
00:19:20,000 --> 00:19:22,000
Huwa ta 'funzjoni identika jismu.

359
00:19:22,000 --> 00:19:25,000
Just tgħaddiha problema iżgħar u iżgħar kull darba,

360
00:19:25,000 --> 00:19:28,000
u anke jekk aħna għandna affarijiet mhux pjuttost formalizzati fil-kodiċi hawn

361
00:19:28,000 --> 00:19:33,000
dan huwa eżattament dak li kien għaddej fl-f'ġimgħa 0 mal-ktieb tat-telefon.

362
00:19:33,000 --> 00:19:36,000
Dan huwa eżattament dak li kien għaddej fil-ġimgħat li għaddew ma 'Sean

363
00:19:36,000 --> 00:19:39,000
u ma 'dimostrazzjonijiet tagħna ta' tiftix għal numri.

364
00:19:39,000 --> 00:19:42,000
Huwa jieħu problema u jiġi diviż mill-ġdid u għal darb'oħra.

365
00:19:42,000 --> 00:19:44,000
>> Fi kliem ieħor, hemm mod issa 'traduzzjoni

366
00:19:44,000 --> 00:19:47,000
din tibni dinja reali, dan tibni livell ogħla

367
00:19:47,000 --> 00:19:51,000
ta jaqsam u jirbħu u tagħmel xi ħaġa għal darb'oħra u għal darb'oħra

368
00:19:51,000 --> 00:19:56,000
fil-kodiċi, għalhekk din hija xi ħaġa aħna se tara mill-ġdid matul iż-żmien.

369
00:19:56,000 --> 00:20:00,000
Issa, bħala twarrib, jekk int ġodda għall recursion inti għandek inqas jifhmu issa

370
00:20:00,000 --> 00:20:02,000
għaliex dan huwa umoristiċi.

371
00:20:02,000 --> 00:20:05,000
Jien ser tmur google.com,

372
00:20:05,000 --> 00:20:17,000
u jien ser tfittex xi tips u tricks fuq recursion, jidħol.

373
00:20:17,000 --> 00:20:21,000
Għid il-persuna li jmiss lilek jekk dawn ma kinux laughing biss issa.

374
00:20:21,000 --> 00:20:23,000
Ridt tfisser recursion?

375
00:20:23,000 --> 00:20:25,000
Ridt tfisser 'ah, hemm we go.

376
00:20:25,000 --> 00:20:28,000
Okay, issa li l-bqija ta 'kulħadd.

377
00:20:28,000 --> 00:20:30,000
A bajd tal-Għid ftit inkorporat x'imkien hemmhekk fil-Google.

378
00:20:30,000 --> 00:20:33,000
Bħala twarrib, wieħed mill-links li nitfgħu fuq il-websajt tal-kors tal-

379
00:20:33,000 --> 00:20:36,000
għal-lum huwa biss dan grilja ta 'algoritmi issortjar varji,

380
00:20:36,000 --> 00:20:39,000
wħud minnhom ħarisna lejn il-ġimgħa li għaddiet, imma x'hemm sbieħ dwar dan viżwalizzazzjoni

381
00:20:39,000 --> 00:20:43,000
kif inti tipprova wrap moħħok madwar affarijiet varji relatati ma 'algoritmi

382
00:20:43,000 --> 00:20:46,000
taf li inti tista 'faċilment issa tibda ma' tipi differenti ta 'inputs.

383
00:20:46,000 --> 00:20:50,000
L-inputs kollha maqluba, l-inputs l-aktar magħżula, l-inputs każwali u ibqa 'sejjer hekk.

384
00:20:50,000 --> 00:20:53,000
Kif inti tipprova, għal darb'oħra, jiddistingwu dawn l-affarijiet fil-moħħ tiegħek

385
00:20:53,000 --> 00:20:57,000
jirrealizzaw li dan il-URL fuq il-websajt il-kors dwar il-paġna Lectures

386
00:20:57,000 --> 00:21:00,000
jistgħu jgħinuk raġuni permezz xi wħud minn dawk.

387
00:21:00,000 --> 00:21:05,000
>> Illum aħna finalment nikseb biex issolvi din il-problema minn ftit lura,

388
00:21:05,000 --> 00:21:08,000
li kien li din il-funzjoni tpartit biss ma 'xogħol,

389
00:21:08,000 --> 00:21:12,000
u dak li kien il-problema fundamentali ma 'dan tpartit funzjoni,

390
00:21:12,000 --> 00:21:15,000
l-għan tagħha kien, għal darb'oħra, biex jiskambjaw valur hawn u hawn

391
00:21:15,000 --> 00:21:17,000
b'tali mod li dan jiġri?

392
00:21:17,000 --> 00:21:20,000
Dan ma attwalment jaħdmu. Għaliex?

393
00:21:20,000 --> 00:21:22,000
Yeah.

394
00:21:22,000 --> 00:21:28,000
[Inaudible-istudent]

395
00:21:28,000 --> 00:21:31,000
Eżattament, l-ispjegazzjoni għal din bugginess

396
00:21:31,000 --> 00:21:34,000
sempliċement għaliex kien meta inti sejħa funzjonijiet C

397
00:21:34,000 --> 00:21:38,000
u dawk il-funzjonijiet jieħdu l-argumenti, bħal aub hawn,

398
00:21:38,000 --> 00:21:42,000
inti tgħaddi kopji ta 'kwalunkwe valur int jipprovdu għal dik il-funzjoni.

399
00:21:42,000 --> 00:21:46,000
Inti ma jipprovdix il-valuri oriġinali infushom,

400
00:21:46,000 --> 00:21:49,000
hekk aħna raw dan fil-kuntest ta 'buggyc,

401
00:21:49,000 --> 00:21:52,000
buggy3.c, li ħares ftit xi ħaġa bħal din.

402
00:21:52,000 --> 00:21:57,000
>> Ifakkar li kellna x uy initialized għal 1 u 2, rispettivament.

403
00:21:57,000 --> 00:21:59,000
Aħna mbagħad stampat dak li kienu.

404
00:21:59,000 --> 00:22:03,000
I imbagħad sostna li kien I iskambji lilhom billi ċċempel tpartit ta 'x, y.

405
00:22:03,000 --> 00:22:06,000
Iżda l-problema kienet li l-iskambji maħduma,

406
00:22:06,000 --> 00:22:10,000
iżda biss fl-ambitu tal-iswap jaħdem innifsu.

407
00:22:10,000 --> 00:22:13,000
Hekk kif aħna hit-linja 40 dawk il-valuri biddlu

408
00:22:13,000 --> 00:22:16,000
kienu tintrema, u għalhekk xejn

409
00:22:16,000 --> 00:22:21,000
fil-funzjoni oriġinali ewlenija kienet attwalment nbidel f'xejn,

410
00:22:21,000 --> 00:22:26,000
hekk jekk taħseb lura mbagħad dwar din xi Dehra f'termini ta 'memorja tagħna

411
00:22:26,000 --> 00:22:29,000
jekk din in-naħa tax-xellug tal-bord tirrappreżenta '

412
00:22:29,000 --> 00:22:33,000
u jien ser nagħmlu l-almu tiegħi għal kulħadd biex tara din il-jekk din in-naħa tax-xellug tal-bord

413
00:22:33,000 --> 00:22:37,000
jirrappreżenta, jiġifieri, RAM tiegħek, u l-munzell se jikbru fuq il b'dan il-mod,

414
00:22:37,000 --> 00:22:43,000
u aħna sejħa funzjoni simili ewlenija, u prinċipali għandu 2 varjabbli lokali, xuy,

415
00:22:43,000 --> 00:22:48,000
ejja jiddeskrivu dawk kif x hawnhekk, u ejja jiddeskrivu dawn bħala y hawn,

416
00:22:48,000 --> 00:22:55,000
u ejja tpoġġi fil-valuri 1 u 2, għalhekk dan hawnhekk hija prinċipali,

417
00:22:55,000 --> 00:22:58,000
u meta jitlob il-funzjoni prinċipali tpartit-sistema operattiva

418
00:22:58,000 --> 00:23:02,000
tagħti l-funzjoni tpartit radda tagħha stess ta 'memorja fuq il-munzell,

419
00:23:02,000 --> 00:23:04,000
qafas tagħha stess fuq il-munzell, biex ngħidu hekk.

420
00:23:04,000 --> 00:23:08,000
Hija wkoll jalloka 32 bits għal dawn ints.

421
00:23:08,000 --> 00:23:11,000
Dan jiġri li jsejħu lilhom aub, iżda li l-totalment arbitrarju.

422
00:23:11,000 --> 00:23:13,000
Dan seta 'talab minnhom tkun xi tkun trid, imma x'jiġri meta prinċipali

423
00:23:13,000 --> 00:23:19,000
jistieden tpartit huwa jieħu din 1, ipoġġi kopja hemmhekk, tpoġġi kopja hemmhekk.

424
00:23:19,000 --> 00:23:23,000
>> Hemm 1 varjabbli lokali oħra fl tpartit, għalkemm, imsejħa liema? TMP. >>

425
00:23:23,000 --> 00:23:27,000
TMP, so let me jagħtu myself ieħor bits 32 hawn,

426
00:23:27,000 --> 00:23:29,000
u dak li ma nagħmel f'dan il-funzjoni?

427
00:23:29,000 --> 00:23:34,000
I said TMP int gets, hekk tkun 1, so I ma 'dan meta aħna l-aħħar lagħbu dan l-eżempju.

428
00:23:34,000 --> 00:23:39,000
Imbagħad gets b, hekk b huwa 2, hekk issa dan isir 2,

429
00:23:39,000 --> 00:23:42,000
u issa b gets temperatura, għalhekk temperatura hija ta '1,

430
00:23:42,000 --> 00:23:44,000
hekk issa b isir dan.

431
00:23:44,000 --> 00:23:46,000
Li l-kbir. Hija ħadmet.

432
00:23:46,000 --> 00:23:49,000
Iżda mbagħad hekk kif il-prospetti funzjoni

433
00:23:49,000 --> 00:23:52,000
memorja swap b'mod effettiv tisparixxi sabiex ikun jista 'jiġi użat mill-ġdid

434
00:23:52,000 --> 00:23:58,000
minn xi funzjoni oħra fil-futur, u prinċipali hija ovvjament kompletament mingħajr tibdil.

435
00:23:58,000 --> 00:24:00,000
Għandna bżonn mod ta 'fundamentalment isolvi din il-problema,

436
00:24:00,000 --> 00:24:03,000
u llum aħna ser finalment ikollhom mod ta 'kif isir dan biha

437
00:24:03,000 --> 00:24:06,000
nistgħu jintroduċu xi ħaġa imsejħa pointer.

438
00:24:06,000 --> 00:24:09,000
Jirriżulta li nistgħu issolvi din il-problema

439
00:24:09,000 --> 00:24:12,000
mhux billi tgħaddi kopji ta 'xuy

440
00:24:12,000 --> 00:24:18,000
iżda minflok billi tgħaddi fil dak, taħseb, li l-funzjoni tpartit?

441
00:24:18,000 --> 00:24:20,000
Yeah, dak dwar l-indirizz?

442
00:24:20,000 --> 00:24:22,000
Aħna ma verament tkellem dwar l-indirizzi fid-dettall ħafna,

443
00:24:22,000 --> 00:24:25,000
imma jekk dan blackboard jirrappreżenta memorja tal-kompjuter tiegħi

444
00:24:25,000 --> 00:24:28,000
nistgħu ċertament tibda numerazzjoni-bytes fir RAM tiegħi

445
00:24:28,000 --> 00:24:31,000
u jgħidu dan huwa byte # 1, dan huwa byte # 2, byte # 3,

446
00:24:31,000 --> 00:24:35,000
byte # 4, byte # ... 2 biljun jekk Għandi 2 gigabytes ta 'RAM,

447
00:24:35,000 --> 00:24:38,000
hekk nistgħu ċertament toħroġ ma 'xi skema ta' numerazzjoni arbitrarja

448
00:24:38,000 --> 00:24:41,000
għall-bytes kollha individwali fil-memorja tal-kompjuter tiegħi.

449
00:24:41,000 --> 00:24:43,000
>> X'jiġri jekk minflok meta I call swap

450
00:24:43,000 --> 00:24:47,000
pjuttost milli jgħaddu kopji ta 'xuy

451
00:24:47,000 --> 00:24:51,000
għaliex ma I minflok jgħaddu fl-indirizz ta 'x hawnhekk,

452
00:24:51,000 --> 00:24:55,000
l-indirizz ta 'y hawn, essenzjalment l-indirizz postali

453
00:24:55,000 --> 00:24:59,000
ta 'xuy għaliex imbagħad tpartit, jekk hu infurmat

454
00:24:59,000 --> 00:25:01,000
ta 'l-indirizz fil-memorja ta' xuy,

455
00:25:01,000 --> 00:25:04,000
imbagħad tpartit, jekk aħna mħarrġa lilu ftit,

456
00:25:04,000 --> 00:25:07,000
huwa jista 'potenzjalment issuq għal dak l-indirizz, biex ngħidu hekk,

457
00:25:07,000 --> 00:25:11,000
x, u jibdlu l-għadd hemmhekk, imbagħad issuq fl-indirizz ta 'y,

458
00:25:11,000 --> 00:25:16,000
jibdlu l-għadd hemmhekk, anki waqt li ma attwalment jkollna kopji ta 'dawk il-valuri stess,

459
00:25:16,000 --> 00:25:19,000
hekk anke jekk aħna tkellimna dwar dan bħala memorja prinċipali tal-

460
00:25:19,000 --> 00:25:23,000
u l-memorja din tpartit bħala s-qawwija u l-parti perikoluża 'C

461
00:25:23,000 --> 00:25:28,000
hija li xi funzjoni jistax imiss memorja kullimkien fil-kompjuter,

462
00:25:28,000 --> 00:25:32,000
u dan hija qawwija li inti tista 'tagħmel affarijiet ferm fancy ma' programmi tal-kompjuter fil C.

463
00:25:32,000 --> 00:25:36,000
Dan huwa perikoluż minħabba li inti tista 'wkoll screw up faċilment.

464
00:25:36,000 --> 00:25:39,000
Fil-fatt, wieħed mill-modi l-aktar komuni għall-programmi f'dawn il-jiem li jiġu sfruttati

465
00:25:39,000 --> 00:25:42,000
xorta huwa għal programmer ma jirrealizzaw

466
00:25:42,000 --> 00:25:45,000
li hu jew hi qed jippermettu ta 'data

467
00:25:45,000 --> 00:25:49,000
li tkun miktuba f'post fil-memorja li ma kienx intenzjonat.

468
00:25:49,000 --> 00:25:51,000
>> Per eżempju, hu jew hi jiddikjara firxa ta 'daqs 10

469
00:25:51,000 --> 00:25:56,000
iżda mbagħad aċċidentalment tipprova tqiegħed 11 bytes f'dik firxa ta 'memorja,

470
00:25:56,000 --> 00:25:59,000
u tibda jmissu partijiet ta 'memorja li ma jkunux aktar validi.

471
00:25:59,000 --> 00:26:02,000
Just biex kuntestwali dan, xi wħud minnkom tista 'taf li

472
00:26:02,000 --> 00:26:06,000
software spiss iqajjem inti għal numri tas-serje jew ċwievet reġistrazzjoni,

473
00:26:06,000 --> 00:26:08,000
Photoshop u Word u programmi bħal din.

474
00:26:08,000 --> 00:26:12,000
Jeżistu xquq, peress li xi wħud minnkom jafu, online fejn int tista 'tmexxi programm ftit,

475
00:26:12,000 --> 00:26:14,000
u voila, l-ebda talba aktar għal numru serjali.

476
00:26:14,000 --> 00:26:16,000
Kif huwa li taħdem?

477
00:26:16,000 --> 00:26:21,000
F'ħafna każijiet dawn l-affarijiet huma sempliċement konstatazzjoni fil-kompjuters

478
00:26:21,000 --> 00:26:24,000
test segmenti fil żerijiet attwali tal-kompjuter u dawk

479
00:26:24,000 --> 00:26:28,000
fejn huwa dik il-funzjoni fejn in-numru tas-serje hija mitluba,

480
00:26:28,000 --> 00:26:31,000
u inti jissostitwixxu l-ispazju, jew waqt li l-programm qed taħdem

481
00:26:31,000 --> 00:26:33,000
inti tista 'ċifra barra fejn il-muftieħ huwa attwalment maħżuna

482
00:26:33,000 --> 00:26:37,000
użu xi ħaġa imsejħa debugger, u inti tista 'qasma li softwer il-mod.

483
00:26:37,000 --> 00:26:40,000
Dan ma jfissirx li dan huwa l-għan tagħna għall-koppja li jmiss ta 'jiem,

484
00:26:40,000 --> 00:26:42,000
iżda għandha ħafna tad-dinja reali ramifikazzjonijiet.

485
00:26:42,000 --> 00:26:45,000
Li wieħed jiġri li jinvolvu serq ta 'software,

486
00:26:45,000 --> 00:26:47,000
imma hemm ukoll kompromess ta 'magni sħaħ.

487
00:26:47,000 --> 00:26:50,000
>> Fil-fatt, meta websajts dawn il-jiem huma sfruttati

488
00:26:50,000 --> 00:26:53,000
u kompromessi u data nixxew u passwords huma misruqa

489
00:26:53,000 --> 00:26:58,000
dan ħafna drabi relatat ma 'ġestjoni ħażina tal-memorja wieħed,

490
00:26:58,000 --> 00:27:01,000
jew, fil-każ ta 'databases, in-nuqqas li jiġu antiċipati

491
00:27:01,000 --> 00:27:03,000
input tal-kontradittorju, b'mod aktar fuq li fil-ġimgħat li ġejjin,

492
00:27:03,000 --> 00:27:07,000
iżda għal issa biss Sneak preview tal-tip ta 'ħsara li inti tista' tagħmel

493
00:27:07,000 --> 00:27:11,000
billi ma pjuttost jifhmu kif jaħdmu l-affarijiet minn taħt il-barnuża.

494
00:27:11,000 --> 00:27:14,000
Ejja tmur dwar fehim għaliex dan huwa miksur

495
00:27:14,000 --> 00:27:17,000
ma 'għodda li se jsiru aktar u aktar utli

496
00:27:17,000 --> 00:27:19,000
bħala programmi tagħna jiksbu aktar kumplessi.

497
00:27:19,000 --> 00:27:21,000
S'issa meta inti kellna bug fil-programm tiegħek

498
00:27:21,000 --> 00:27:23,000
kif inti marret dwar debugging dan?

499
00:27:23,000 --> 00:27:25,000
Liema kienu tekniki tiegħek kienu s'issa, kemm jekk mgħallma minn TF tiegħek

500
00:27:25,000 --> 00:27:27,000
jew biss awto-mgħallma?

501
00:27:27,000 --> 00:27:29,000
[Student] printf.

502
00:27:29,000 --> 00:27:31,000
Printf, hekk printf x'aktarx ilha ħabib tiegħek li jekk inti tixtieq li tara

503
00:27:31,000 --> 00:27:33,000
x'inhu għaddej ġewwa tal-programm tiegħek

504
00:27:33,000 --> 00:27:36,000
inti biss jitqiegħed printf hawn, printf hawn, printf hawn.

505
00:27:36,000 --> 00:27:38,000
Imbagħad inti run, u inti tikseb mazz sħiħ ta 'għalf fuq l-iskrin

506
00:27:38,000 --> 00:27:43,000
li tista 'tuża biex imbagħad jiġi dedott dak li huwa attwalment tmur ħażina fil-programm tiegħek.

507
00:27:43,000 --> 00:27:45,000
>> Printf tendenza li tkun ħaġa qawwija ħafna,

508
00:27:45,000 --> 00:27:47,000
iżda huwa proċess ferm manwali.

509
00:27:47,000 --> 00:27:49,000
Int għandek tpoġġi printf hawn, a printf hawn,

510
00:27:49,000 --> 00:27:51,000
u jekk inti tpoġġi ġewwa ta 'linja inti tista' tikseb 100 linji

511
00:27:51,000 --> 00:27:53,000
tal-produzzjoni li inti mbagħad ikollhom biex jiġu ffiltrati permezz.

512
00:27:53,000 --> 00:27:58,000
Mhuwiex mekkaniżmu ħafna faċli għall-utent jew interattivi għall-programmi debugging,

513
00:27:58,000 --> 00:28:00,000
iżda Thankfully teżisti alternattivi.

514
00:28:00,000 --> 00:28:03,000
Hemm programm, per eżempju, imsejħa GDB, il Debugger GNU,

515
00:28:03,000 --> 00:28:06,000
li huwa arcane ftit fil-mod kif tużah.

516
00:28:06,000 --> 00:28:08,000
Huwa kumpless ftit, iżda franchement,

517
00:28:08,000 --> 00:28:11,000
din hija waħda minn dawk l-affarijiet fejn jekk inti tpoġġi fil din il-ġimgħa u li jmiss

518
00:28:11,000 --> 00:28:14,000
il siegħa żejda li wieħed jifhem xi ħaġa bħal GDB

519
00:28:14,000 --> 00:28:18,000
se tiffranka probabbilment għexieren ta 'sigħat fit-tul,

520
00:28:18,000 --> 00:28:21,000
hekk ma 'dan, let me jagħtuk teaser ta' kif dan il-ħaġa xogħlijiet.

521
00:28:21,000 --> 00:28:23,000
>> Jien fil tieqa terminal tiegħi.

522
00:28:23,000 --> 00:28:26,000
Let me imorru quddiem u jiġbru dan il-programm, buggy3.

523
00:28:26,000 --> 00:28:28,000
Huwa diġà aġġornata.

524
00:28:28,000 --> 00:28:31,000
Let me run eżatt bħal għamilna lura waqt, u fil-fatt, huwa imkisser.

525
00:28:31,000 --> 00:28:34,000
Iżda għaliex hija din? Maybe I invitat l-funzjoni tpartit.

526
00:28:34,000 --> 00:28:37,000
Forsi huwa au b. Jien ma pjuttost jiċċaqalqu minnhom madwar korrett.

527
00:28:37,000 --> 00:28:39,000
Let me imorru quddiem u jagħmlu dan.

528
00:28:39,000 --> 00:28:43,000
Pjuttost milli sempliċiment run buggy3 let me minflok run din GDB programm,

529
00:28:43,000 --> 00:28:48,000
u jien ser jgħidlek li jimxu buggy3,

530
00:28:48,000 --> 00:28:52,000
u jien ser jinkludi argument linja tal-kmand, TUI-,

531
00:28:52,000 --> 00:28:55,000
u aħna ser tpoġġi dan fil-problemi futuri fil spec biex tfakkar.

532
00:28:55,000 --> 00:28:57,000
U issa din l-interfaċċa iswed u abjad popped up li, għal darb'oħra,

533
00:28:57,000 --> 00:28:59,000
huwa ftit kbira fl-ewwel għaliex hemm dan kollu

534
00:28:59,000 --> 00:29:02,000
informazzjoni garanzija stabbiliti hawn, iżda mill-inqas hemm xi ħaġa familjari.

535
00:29:02,000 --> 00:29:04,000
Fil-quċċata tat-tieqa hija kodiċi attwali tiegħi,

536
00:29:04,000 --> 00:29:08,000
u jekk I iscroll up hawn let me iscroll għall-quċċata tal-fajl tiegħi,

537
00:29:08,000 --> 00:29:11,000
u fil-fatt, hemm buggy3.c, u avviż fil-qiegħ ta 'dan tieqa

538
00:29:11,000 --> 00:29:13,000
Għandi dan pront GDB.

539
00:29:13,000 --> 00:29:16,000
>> Din mhix l-istess bħal fil-pront Harvard tiegħi normali John.

540
00:29:16,000 --> 00:29:19,000
Dan huwa fil-pront li għaddej biex ippermettuli biex jikkontrollaw GDB.

541
00:29:19,000 --> 00:29:21,000
GDB huwa debugger.

542
00:29:21,000 --> 00:29:24,000
A debugger huwa programm li ihallik timxi permezz

543
00:29:24,000 --> 00:29:27,000
eżekuzzjoni tal-linja program tiegħek billi linja b'linja,

544
00:29:27,000 --> 00:29:30,000
tul it-triq tagħmel xejn inti tixtieq li l-programm,

545
00:29:30,000 --> 00:29:33,000
anke ssejjaħ funzjonijiet, jew tfittex, aktar importanti,

546
00:29:33,000 --> 00:29:35,000
fil-valuri varjabbli varji ta.

547
00:29:35,000 --> 00:29:37,000
Ejja imorru quddiem u jagħmlu dan.

548
00:29:37,000 --> 00:29:40,000
Jien ser jimxi 'l quddiem u t-tip fil-medda t fil-pront GDB s,

549
00:29:40,000 --> 00:29:43,000
hekk avviż fil-qiegħ tax-xellug tal-iskrin stajt ittajpjat run,

550
00:29:43,000 --> 00:29:45,000
u stajt hit jidħol, u dak li ma din tagħmel?

551
00:29:45,000 --> 00:29:50,000
Hija litteralment dam programm tiegħi, imma jien ma attwalment tara ħafna jmorru fuq hawn

552
00:29:50,000 --> 00:29:55,000
minħabba I ma attwalment qal lill-debugger

553
00:29:55,000 --> 00:29:57,000
biex nieqaf f'mument partikolari fil-ħin.

554
00:29:57,000 --> 00:29:59,000
Just ttajpjati run tiġġestixxi l-programm.

555
00:29:59,000 --> 00:30:01,000
I ma attwalment tara xejn. I ma tista 'timmanipola dan.

556
00:30:01,000 --> 00:30:03,000
>> Minflok let me tagħmel dan.

557
00:30:03,000 --> 00:30:08,000
F'dan pront GDB let me minflok tip break, jidħol.

558
00:30:08,000 --> 00:30:10,000
Li mhux dak I fisser it-tip.

559
00:30:10,000 --> 00:30:13,000
Ejja minflok tip break prinċipali.

560
00:30:13,000 --> 00:30:15,000
Fi kliem ieħor, nixtieq li jistabbilixxu xi ħaġa imsejħa breakpoint,

561
00:30:15,000 --> 00:30:18,000
li huwa adattat issemmiet għaliex se waqfa jew pawża

562
00:30:18,000 --> 00:30:21,000
eżekuzzjoni tal-programm tiegħek f'dak il-post partikolari.

563
00:30:21,000 --> 00:30:23,000
Main huwa l-isem tal-funzjoni tiegħi.

564
00:30:23,000 --> 00:30:25,000
Avviż li GDB hija pjuttost intelliġenti.

565
00:30:25,000 --> 00:30:28,000
Hija dehret li jiġri prinċipali biex tibda ftit jew wisq fl linja 18

566
00:30:28,000 --> 00:30:32,000
ta buggy3.c, u mbagħad avviż hawn fuq quċċata xellug

567
00:30:32,000 --> 00:30:34,000
b + huwa dritt li jmiss għal-linja 18.

568
00:30:34,000 --> 00:30:38,000
Li fakkruha me I waqqfu breakpoint fil-linja 18.

569
00:30:38,000 --> 00:30:42,000
Din id-darba meta I tip run, jien ser jimxu programm tiegħi

570
00:30:42,000 --> 00:30:45,000
up sakemm hits li breakpoint,

571
00:30:45,000 --> 00:30:48,000
għalhekk il-programm se nieqaf għalija fil-linja 18.

572
00:30:48,000 --> 00:30:50,000
Here we go, run.

573
00:30:50,000 --> 00:30:53,000
Xejn jidher li ġara, iżda l-avviż fil-qiegħ xellug

574
00:30:53,000 --> 00:30:58,000
Programm bidu, buggy3, breakpoint 1 fil prinċipali fil-linja buggy3.c 18.

575
00:30:58,000 --> 00:31:00,000
X'nista 'nagħmel issa?

576
00:31:00,000 --> 00:31:03,000
>> Avviż I tista 'tibda ittajpjar affarijiet simili stampati,

577
00:31:03,000 --> 00:31:08,000
ma printf, x jistampa, u issa thats stramba.

578
00:31:08,000 --> 00:31:11,000
Il-$ 1 huwa biss kurżità, kif Ser naraw

579
00:31:11,000 --> 00:31:14,000
kull darba li inti print xi ħaġa ikollok ġdid $ valur.

580
00:31:14,000 --> 00:31:18,000
Dak sabiex inti tista 'tirreferi lura għall-valuri ta' qabel biss fil-każ,

581
00:31:18,000 --> 00:31:21,000
iżda għal issa dak istampar hija me javżak huwa li l-valur ta 'x f'dan il-punt fl-istorja

582
00:31:21,000 --> 00:31:26,000
hija apparentement 134514032.

583
00:31:26,000 --> 00:31:29,000
What? Fejn ma li anke jiġu minn?

584
00:31:29,000 --> 00:31:31,000
[Inaudible-istudent]

585
00:31:31,000 --> 00:31:34,000
Tabilħaqq, dan huwa dak li aħna ser sejħa valur żibel, u konna ma tkellem dwar dan għadha,

586
00:31:34,000 --> 00:31:37,000
iżda r-raġuni li inti initialize-varjabbli

587
00:31:37,000 --> 00:31:40,000
huwa ovvjament sabiex ikollhom xi valur li inti tixtieq li jkollok.

588
00:31:40,000 --> 00:31:44,000
Iżda l-qabda tfakkar li inti tista 'tiddikjara varjabbli

589
00:31:44,000 --> 00:31:46,000
bħal I ma mument ilu fl-eżempju sigma tiegħi

590
00:31:46,000 --> 00:31:48,000
mingħajr ma attwalment jagħtihom valur.

591
00:31:48,000 --> 00:31:50,000
Recall dak li għamilt hawn fuq fil sigma.

592
00:31:50,000 --> 00:31:52,000
I ddikjarat n, iżda liema valur ma nagħti dan?

593
00:31:52,000 --> 00:31:56,000
Xejn, għaliex kont naf li fil-linji li ġejjin

594
00:31:56,000 --> 00:31:59,000
GetInt se tieħu ħsieb il-problema ta 'tqegħid ta' valur ġewwa ta 'n.

595
00:31:59,000 --> 00:32:02,000
>> Iżda f'dan il-punt fl-istorja tal-linja 11

596
00:32:02,000 --> 00:32:05,000
u l-linja 12 u linja 13 u l-linja 14

597
00:32:05,000 --> 00:32:08,000
matul dawk il-linji diversi x'inhu l-valur ta 'n?

598
00:32:08,000 --> 00:32:10,000
Fil Ċ inti biss ma nafx.

599
00:32:10,000 --> 00:32:14,000
Huwa ġeneralment xi valur żibel, xi numru kompletament bl-addoċċ

600
00:32:14,000 --> 00:32:17,000
li ħalla fuq essenzjalment minn xi funzjoni ta 'qabel

601
00:32:17,000 --> 00:32:21,000
li tkun għamlet, sabiex il-programm tiegħek runs

602
00:32:21,000 --> 00:32:24,000
ifakkar li l-funzjoni gets, funzjoni funzjoni, il-funzjoni.

603
00:32:24,000 --> 00:32:27,000
Kollha dawn il-frejms nikseb jitqiegħdu fuq il-memorja, u mbagħad dawk ritorn funzjonijiet,

604
00:32:27,000 --> 00:32:31,000
u biss bħal I suġġerit bl-Eraser memorja tagħhom huwa eventwalment jerġa 'jintuża.

605
00:32:31,000 --> 00:32:37,000
Ukoll, huwa biss hekk jiġri li dan x-varjabbli f'dan il-programm

606
00:32:37,000 --> 00:32:41,000
jidher li hemm xi valur żibel bħal 134514032

607
00:32:41,000 --> 00:32:44,000
minn xi funzjoni ta 'qabel, mhux wieħed li I kiteb.

608
00:32:44,000 --> 00:32:47,000
Jista 'jkun xi ħaġa li taqa' b'mod effettiv mal-sistema operattiva,

609
00:32:47,000 --> 00:32:49,000
xi funzjoni taħt il-barnuża.

610
00:32:49,000 --> 00:32:52,000
>> Okay, li l-multa, imma ejja issa javvanzaw għal-linja li jmiss.

611
00:32:52,000 --> 00:32:55,000
Jekk I tip "li jmiss" fil-pront GDB tiegħi u I hit jidħol,

612
00:32:55,000 --> 00:32:58,000
tinnota li l-enfasi jiċċaqlaq isfel għal-linja 19,

613
00:32:58,000 --> 00:33:01,000
iżda l-implikazzjoni loġika hija dik il-linja 18

614
00:33:01,000 --> 00:33:06,000
issa lest eżekuzzjoni, hekk jekk I darb'oħra tip "print x"

615
00:33:06,000 --> 00:33:10,000
I issa għandhom jaraw 1, u fil-fatt, I do.

616
00:33:10,000 --> 00:33:14,000
Għal darb'oħra, l-għalf $ huwa mod ta 'GDB nfarkkarkom

617
00:33:14,000 --> 00:33:17,000
dak li l-istorja ta 'prints huma li inti ghamilt.

618
00:33:17,000 --> 00:33:21,000
Issa let me aqbad u jistampa y, u fil-fatt, y hija xi valur crazy kif ukoll,

619
00:33:21,000 --> 00:33:24,000
iżda l-ebda big deal għaliex linja 19 aħna qed dwar li tassenja din

620
00:33:24,000 --> 00:33:27,000
il-valur 2, so let me tip "li jmiss" darb'oħra.

621
00:33:27,000 --> 00:33:29,000
U issa aħna qed fuq il-linja printf.

622
00:33:29,000 --> 00:33:31,000
Let me do x istampar.

623
00:33:31,000 --> 00:33:34,000
Let me do y print. Franchement, jien jkollna ftit għajjien ta 'stampar dan.

624
00:33:34,000 --> 00:33:38,000
Let me minflok tip "x display" u "wirja y,"

625
00:33:38,000 --> 00:33:41,000
u issa kull darba I tip ta 'kmand fil-futur

626
00:33:41,000 --> 00:33:45,000
I se jiġu mfakkra ta 'x'hemm xuy, x'hemm xuy, x'hemm xuy.

627
00:33:45,000 --> 00:33:48,000
>> I tista 'wkoll, bħala twarrib, tip "lokal info."

628
00:33:48,000 --> 00:33:50,000
Info huwa kmand speċjali.

629
00:33:50,000 --> 00:33:52,000
Lokal jfisser li turi lili l-varjazzjonijiet lokali.

630
00:33:52,000 --> 00:33:55,000
Biss fil-każ ninsa jew din hija crazy, funzjoni kkumplikata

631
00:33:55,000 --> 00:33:57,000
li jien jew xi ħadd ieħor kiteb lokal info se jgħidlek

632
00:33:57,000 --> 00:34:00,000
liema huma l-varjazzjonijiet lokali tal ġewwa din il-funzjoni lokali

633
00:34:00,000 --> 00:34:03,000
li inti tista 'kura dwar jekk inti tixtieq li poke madwar.

634
00:34:03,000 --> 00:34:07,000
Issa, printf ikun wasal biex tesegwixxi, so let me imorru quddiem u biss tip "li jmiss."

635
00:34:07,000 --> 00:34:10,000
Għaliex aħna qed f'dan l-ambjent aħna mhux qed fil-fatt dan iqisuh

636
00:34:10,000 --> 00:34:14,000
tesegwixxi stabbiliti hawn, iżda avviż huwa jkollna ftit mangled hawn.

637
00:34:14,000 --> 00:34:17,000
Iżda l-avviż huwa prevalenti l-iskrin hemm,

638
00:34:17,000 --> 00:34:21,000
hekk huwa mhux programm perfetta hawn, iżda li okay minħabba I jistgħu dejjem poke madwar

639
00:34:21,000 --> 00:34:23,000
użu print jekk irrid.

640
00:34:23,000 --> 00:34:26,000
>> Let me tip li jmiss darb'oħra, u issa hawnhekk l-parti interessanti.

641
00:34:26,000 --> 00:34:29,000
Fuq dan il-punt fl-istorja y huwa 2, u x hija l-1,

642
00:34:29,000 --> 00:34:32,000
kif issuġġerit hawnhekk, u għal darb'oħra,

643
00:34:32,000 --> 00:34:35,000
ir-raġuni dan huwa awtomatikament wiri issa huwa minħabba I użat il-kmand

644
00:34:35,000 --> 00:34:40,000
wiri u l-wiri x y, sabiex il-mument I tip li jmiss

645
00:34:40,000 --> 00:34:43,000
fit-teorija xuy għandhom isiru skambjati.

646
00:34:43,000 --> 00:34:45,000
Issa, aħna diġà jafu li mhux se jkun il-każ,

647
00:34:45,000 --> 00:34:49,000
iżda Ser naraw fil-mument kif nistgħu adsa aktar profonda biex insemmu għaliex dan huwa veru.

648
00:34:49,000 --> 00:34:54,000
Sussegwentement, u sfortunatament, y għadu 2 u x għadu 1, u nista 'nikkonferma kemm.

649
00:34:54,000 --> 00:34:56,000
Stampa x, y print.

650
00:34:56,000 --> 00:34:59,000
Tabilħaqq, l-ebda iskambji fil-fatt ġara, hekk ejja nibdew dan fuq.

651
00:34:59,000 --> 00:35:01,000
Ovvjament tpartit hija maqsuma.

652
00:35:01,000 --> 00:35:04,000
Ejja minflok tip "run" darb'oħra.

653
00:35:04,000 --> 00:35:07,000
Let me say yes, nixtieq li terġa 'tibda mill-bidu, jidħol.

654
00:35:07,000 --> 00:35:09,000
>> Issa jien back-up fil-linja 18.

655
00:35:09,000 --> 00:35:11,000
Issa avviż xuy huma valuri taż-żibel mill-ġdid.

656
00:35:11,000 --> 00:35:15,000
Sussegwentement, wara dan, li jmiss, li jmiss.

657
00:35:15,000 --> 00:35:17,000
Jekk niġi bored I tista 'wkoll biss tip n li jmiss.

658
00:35:17,000 --> 00:35:21,000
Tista 'jqassar dan il-sekwenza iqsar possibbli ta' karattri.

659
00:35:21,000 --> 00:35:23,000
Swap issa hija maqsuma.

660
00:35:23,000 --> 00:35:25,000
Ejja adsa fi, hekk minflok ta 'tajping li jmiss,

661
00:35:25,000 --> 00:35:30,000
Issa jien se tip pass hekk li jien titjib ġewwa ta 'din il-funzjoni

662
00:35:30,000 --> 00:35:33,000
sabiex I tista 'timxi permezz ta' dan, so I hit pass u mbagħad tidħol.

663
00:35:33,000 --> 00:35:37,000
Avviż li l jumps tenfasizza l isfel aktar baxx fil-programm tiegħi għal-linja 36.

664
00:35:37,000 --> 00:35:39,000
Issa liema huma l-fatturi varjabbli lokali?

665
00:35:39,000 --> 00:35:41,000
Info lokal.

666
00:35:41,000 --> 00:35:43,000
Xejn għadha biss għaliex aħna stajt ma gotten għal dik il-linja,

667
00:35:43,000 --> 00:35:47,000
hekk ejja imorru quddiem u jgħidu "li jmiss."

668
00:35:47,000 --> 00:35:50,000
Issa għandna jidhru li jkollhom TMP TMP istampar,.

669
00:35:50,000 --> 00:35:52,000
Valur Żibel, id-dritt? I think so.

670
00:35:52,000 --> 00:35:55,000
Kif dwar tipprintja b istampar,, 1 u 2?

671
00:35:55,000 --> 00:35:58,000
Fil-mument, malli I tip li jmiss darb'oħra

672
00:35:58,000 --> 00:36:02,000
TMP huwa ser jieħu fuq valur ta '1, wieħed jittama,

673
00:36:02,000 --> 00:36:05,000
minħabba TMP se jiġu assenjati l-valur ta '.

674
00:36:05,000 --> 00:36:08,000
>> Issa ejja do tistampa b istampar,,

675
00:36:08,000 --> 00:36:11,000
iżda issa jistampaw TMP, u huwa tabilħaqq 1.

676
00:36:11,000 --> 00:36:14,000
Let me jagħmlu li jmiss. Let me jagħmlu li jmiss.

677
00:36:14,000 --> 00:36:16,000
Stajt lest il-funzjoni tpartit.

678
00:36:16,000 --> 00:36:19,000
Jien xorta ġewwa ta 'dan fil-linja 40, so let me jistampaw,

679
00:36:19,000 --> 00:36:22,000
istampar b, u jien ma 'kura huwa TMP dak.

680
00:36:22,000 --> 00:36:27,000
Jidher qisu swap hija korretta meta niġu għall-iskambji aub.

681
00:36:27,000 --> 00:36:31,000
Imma jekk jien issa tip li jmiss, I Mur lura għall-linja 25,

682
00:36:31,000 --> 00:36:34,000
u ta 'kors, jekk I tip fil x u tistampa y

683
00:36:34,000 --> 00:36:38,000
dawn qed għadhom ma nbidlux, hekk aħna mhux fiss il-problema.

684
00:36:38,000 --> 00:36:41,000
Imma diagnostically issa forsi ma dan il-programm GDB

685
00:36:41,000 --> 00:36:44,000
konna inqas gotten pass eqreb lejn fehim

686
00:36:44,000 --> 00:36:47,000
x'inhu għaddej ħażin mingħajr ma jkollhom mifrex kodiċi tagħna billi jpoġġi printf hawn,

687
00:36:47,000 --> 00:36:50,000
printf hawn, printf hawn u mbagħad-tmexxija mill-ġdid u għal darb'oħra

688
00:36:50,000 --> 00:36:52,000
jippruvaw ċifra barra dak li għaddej ħażin.

689
00:36:52,000 --> 00:36:55,000
>> Jien ser jimxi 'l quddiem u nieqaf minn dan għal kollox nieqaf.

690
00:36:55,000 --> 00:36:57,000
Huwa ser mbagħad jgħidu, "Nieqaf xorta?" Iva.

691
00:36:57,000 --> 00:37:00,000
Issa jien lura fil-pront normali tiegħi, u jien jsir użu GDB.

692
00:37:00,000 --> 00:37:03,000
Bħala twarrib, inti m'għandekx bżonn li jużaw dan TUI-bandiera.

693
00:37:03,000 --> 00:37:07,000
Fil-fatt, jekk inti tonqos li tikseb essenzjalment l-nofs ta 'isfel tal-iskrin.

694
00:37:07,000 --> 00:37:11,000
Jekk I imbagħad tip waqfa prinċipali u mbagħad run

695
00:37:11,000 --> 00:37:15,000
I xorta jistgħu run program tiegħi, imma dak li se tagħmel huwa aktar testwalment

696
00:37:15,000 --> 00:37:18,000
biss juru lili il-linja waħda kurrenti fi żmien.

697
00:37:18,000 --> 00:37:21,000
Il TUI-, user interface testwali,

698
00:37:21,000 --> 00:37:25,000
biss turi inti aktar tal-programm fil-darba, li hija probabbilment daqsxejn kunċettwali aktar faċli.

699
00:37:25,000 --> 00:37:27,000
Imma fil-fatt, I tista 'biss tagħmel li jmiss, li jmiss, li jmiss,

700
00:37:27,000 --> 00:37:30,000
u jien ser tara linja waħda fi żmien, u jekk I really trid tara x'inhu għaddej

701
00:37:30,000 --> 00:37:35,000
I tista tip lista u tara mazz sħiħ ta 'linji ġirien.

702
00:37:35,000 --> 00:37:39,000
>> Hemm video li konna mitluba li inti watch għall-problema settijiet 3

703
00:37:39,000 --> 00:37:43,000
fejn Nate tkopri wħud mill-intricacies ta 'GDB,

704
00:37:43,000 --> 00:37:46,000
u din hija waħda minn dawk l-affarijiet, onestament, fejn xi persentaġġ mhux trivjali tal inti

705
00:37:46,000 --> 00:37:49,000
qatt se touch GDB, u li se tkun ħaġa ħażina

706
00:37:49,000 --> 00:37:53,000
għaliex litteralment inti ser jispiċċaw infiq aktar ħin aktar tard din is-semestru

707
00:37:53,000 --> 00:37:56,000
tmur fl bugs allura inti jekk inti tpoġġi f'dak nofs siegħa / siegħa

708
00:37:56,000 --> 00:38:00,000
din il-ġimgħa u t-tagħlim li jmiss biex tikseb komda mal GDB.

709
00:38:00,000 --> 00:38:02,000
Printf kien ħabib tiegħek.

710
00:38:02,000 --> 00:38:05,000
GDB għandu issa jkun ħabib tiegħek.

711
00:38:05,000 --> 00:38:08,000
>> Kwalunkwe mistoqsijiet dwar GDB?

712
00:38:08,000 --> 00:38:12,000
U hawn lista ta 'malajr ta' xi wħud mill-kmandi aktar qawwija u utli.

713
00:38:12,000 --> 00:38:15,000
Yeah. >> Tista print string?

714
00:38:15,000 --> 00:38:17,000
Tista 'tipprintja string? Assolutament.

715
00:38:17,000 --> 00:38:19,000
Ma għandhom biss ikunu interi.

716
00:38:19,000 --> 00:38:22,000
Jekk i varjabbli huwa string biss tip i print.

717
00:38:22,000 --> 00:38:24,000
Hija ser nuruk dak li varjabbli sekwenza huwa.

718
00:38:24,000 --> 00:38:26,000
[Inaudible-istudent]

719
00:38:26,000 --> 00:38:28,000
Huwa se jagħtik l-indirizz u l-sekwenza nnifisha.

720
00:38:28,000 --> 00:38:32,000
Hija ser nuruk tnejn.

721
00:38:32,000 --> 00:38:34,000
U wieħed aħħar ħaġa, sempliċement minħabba li dawn huma tajba li tkun taf wisq.

722
00:38:34,000 --> 00:38:37,000
Backtrace u l-qafas, let me adsa fis dan iż-żmien l-aħħar wieħed,

723
00:38:37,000 --> 00:38:39,000
Programm eżatt l-istess ma 'GDB.

724
00:38:39,000 --> 00:38:44,000
Let me imorru quddiem u tmexxi l-verżjoni testwali user interface,

725
00:38:44,000 --> 00:38:46,000
break prinċipali.

726
00:38:46,000 --> 00:38:49,000
Let me imorru quddiem u run mill-ġdid. Hawnhekk I am.

727
00:38:49,000 --> 00:38:55,000
Issa let me go jmiss, li jmiss, li jmiss, li jmiss, li jmiss, pass, jidħol.

728
00:38:55,000 --> 00:39:00,000
>> U issa jissoponi Jien issa fil tpartit deliberatament, imma jien simili "indanna, dak li kien il-valur ta 'x?"

729
00:39:00,000 --> 00:39:02,000
I ma tistax tagħmel x aktar.

730
00:39:02,000 --> 00:39:05,000
I ma tistax tagħmel y għaliex dawn mhux qed fl-iskop.

731
00:39:05,000 --> 00:39:07,000
Huma qed mhux fil-kuntest, iżda l-ebda problema.

732
00:39:07,000 --> 00:39:09,000
I tista tip backtrace.

733
00:39:09,000 --> 00:39:13,000
Li turi lili kollha tal-funzjonijiet li jkunu eżegwiti sa dan il-punt fil-ħin.

734
00:39:13,000 --> 00:39:16,000
Avviż li l-wieħed fuq il-qiegħ, prinċipali, linji up ma 'prinċipali

735
00:39:16,000 --> 00:39:18,000
qegħdin fuq il-qiegħ tal-istampa tagħna hawn.

736
00:39:18,000 --> 00:39:22,000
Il-fatt li swap hija ogħla huwa linji bi tpartit tkun il-fuq fil-memorja hawn,

737
00:39:22,000 --> 00:39:26,000
u jekk I rridu nġibu lura għall prinċipali temporanjament nista 'ngħid "qafas".

738
00:39:26,000 --> 00:39:30,000
X'inhu n-numru? Prinċipali huwa frame # 1.

739
00:39:30,000 --> 00:39:32,000
Jien ser jimxi 'l quddiem u jgħidu "qafas 1."

740
00:39:32,000 --> 00:39:36,000
>> Issa jien lura fl prinċipali, u I jistgħu jistampaw x, u I jistgħu jistampaw y,

741
00:39:36,000 --> 00:39:40,000
imma ma nistax jistampaw b jew.

742
00:39:40,000 --> 00:39:43,000
Imma nista 'jekk I say, "Okay, stenna minuta. Fejn kien il-iswap?"

743
00:39:43,000 --> 00:39:46,000
Let me imorru quddiem u jgħidu "0 frame."

744
00:39:46,000 --> 00:39:48,000
Issa jien lura fejn nixtieq li jkun, u bħala twarrib,

745
00:39:48,000 --> 00:39:52,000
hemm jikkmanda oħra wkoll, bħall jekk int verament jkollna bored ittajpjar jmiss, li jmiss, li jmiss, li jmiss,

746
00:39:52,000 --> 00:39:56,000
inti tista 'ġeneralment jgħidu affarijiet simili "10 li jmiss," u li se pass permezz-10 linji.

747
00:39:56,000 --> 00:39:59,000
Tista 'wkoll tikteb "tkompli" meta inti verament tikseb mitmugħa bl titjib permezz tiegħu.

748
00:39:59,000 --> 00:40:05,000
Kompli se jimxu program tiegħek mingħajr interruzzjoni sakemm hits ieħor breakpoint,

749
00:40:05,000 --> 00:40:07,000
kemm jekk loop jew aktar 'l isfel fil-programm tiegħek.

750
00:40:07,000 --> 00:40:11,000
>> F'dan il-każ aħna kompliet l-aħħar, u l-programm ħareġ normalment.

751
00:40:11,000 --> 00:40:13,000
Dan huwa mod fancy, proċess inferjuri.

752
00:40:13,000 --> 00:40:16,000
Just programm tiegħek ħareġ normalment.

753
00:40:16,000 --> 00:40:24,000
Aktar dwar dan fil-video u debugging sessjonijiet li ġejjin.

754
00:40:24,000 --> 00:40:26,000
Dan kien ħafna.

755
00:40:26,000 --> 00:40:35,000
Ejja tieħu 5-minuta break tagħna hawn, u aħna ser terġa 'lura mal structs u fajls.

756
00:40:35,000 --> 00:40:38,000
>> Jekk għandek dived fis pset din il-ġimgħa diġà

757
00:40:38,000 --> 00:40:41,000
inti ser tkun taf li aħna nużaw fil-kodiċi ta 'distribuzzjoni,

758
00:40:41,000 --> 00:40:45,000
s-sors kodiċi li nipprovdu lilek bħala punt tat-tluq, xi tekniki ġodda.

759
00:40:45,000 --> 00:40:50,000
B'mod partikolari, aħna introdotti dan il-keyword ġdida msejħa Struct, għall-istruttura,

760
00:40:50,000 --> 00:40:53,000
sabiex inkunu nistgħu joħolqu varjabbli apposta ta 'tipi.

761
00:40:53,000 --> 00:40:57,000
Aħna wkoll introduċa l-kunċett ta 'input fajl fajl I / O, u l-produzzjoni,

762
00:40:57,000 --> 00:41:00,000
u dan huwa sabiex inkunu nistgħu jiffrankaw l-istat

763
00:41:00,000 --> 00:41:03,000
tal-bord ġirja tiegħek għal fajl fuq diska

764
00:41:03,000 --> 00:41:06,000
sabiex il-fellows tagħlim u I jistgħu jifhmu

765
00:41:06,000 --> 00:41:09,000
x'inhu għaddej ġewwa tal-programm tiegħek mingħajr ma jkollhom manwalment jilagħbu

766
00:41:09,000 --> 00:41:11,000
għexieren ta 'logħob ta' ġirja.

767
00:41:11,000 --> 00:41:13,000
Nistgħu nagħmlu dan aktar automatedly.

768
00:41:13,000 --> 00:41:18,000
>> Din l-idea ta 'Struct jsolvi problema pjuttost konvinċenti.

769
00:41:18,000 --> 00:41:21,000
Ejja ngħidu li aħna rridu li jimplimentaw xi programm

770
00:41:21,000 --> 00:41:25,000
li b'xi żżomm kont ta 'informazzjoni dwar l-istudenti,

771
00:41:25,000 --> 00:41:28,000
u l-istudenti jista 'jkollhom, per eżempju, ID, isem

772
00:41:28,000 --> 00:41:31,000
u dar f'post bħal Harvard, għalhekk dawn huma 3 biċċiet ta 'informazzjoni

773
00:41:31,000 --> 00:41:34,000
irridu li żżomm madwar, so let me imorru quddiem u tibda tikteb programm ftit hawn,

774
00:41:34,000 --> 00:41:38,000
jinkludu stdio.h.

775
00:41:38,000 --> 00:41:42,000
Let me do jinkludu cs50.h.

776
00:41:42,000 --> 00:41:44,000
U mbagħad tibda l-funzjoni prinċipali tiegħi.

777
00:41:44,000 --> 00:41:46,000
I mhux se jolqot bl-ebda argument linja tal-kmand,

778
00:41:46,000 --> 00:41:49,000
u hawn nixtieq li jkollhom student, hekk jien ser ngħid

779
00:41:49,000 --> 00:41:54,000
student ikollu l-isem, hekk jien se ngħid "isem sekwenza."

780
00:41:54,000 --> 00:41:59,000
Imbagħad jien se ngħid student għandu wkoll ID, id hekk int,

781
00:41:59,000 --> 00:42:03,000
u student ikollu dar, hekk jien ukoll se ngħid "house sekwenza."

782
00:42:03,000 --> 00:42:06,000
Imbagħad I ser tordna dawn ftit aktar nadif bħal dan.

783
00:42:06,000 --> 00:42:11,000
Okay, issa għandi 3 varjabbli li biex jirrappreżentaw student, hekk "student".

784
00:42:11,000 --> 00:42:15,000
>> U issa nixtieq li timla dawn il-valuri, so let me jimxi 'l quddiem u ngħid xi ħaġa simili

785
00:42:15,000 --> 00:42:18,000
"Id = 123."

786
00:42:18,000 --> 00:42:21,000
Isem se tikseb David.

787
00:42:21,000 --> 00:42:24,000
Ejja ngħidu dar hija se tikseb Mather,

788
00:42:24,000 --> 00:42:31,000
u mbagħad jien se jagħmlu xi ħaġa simili arbitrarjament printf ("% s,

789
00:42:31,000 --> 00:42:37,000
li huwa ID% d, jgħix fi s%.

790
00:42:37,000 --> 00:42:41,000
U issa, dak li nixtieq li plagg fil hawn, waħda wara l-oħra?

791
00:42:41,000 --> 00:42:47,000
Isem, id-dar; ritorn 0.

792
00:42:47,000 --> 00:42:50,000
Okay, sakemm I invitat up x'imkien here

793
00:42:50,000 --> 00:42:54,000
Naħseb għandna programm pjuttost tajba li taħżen wieħed student.

794
00:42:54,000 --> 00:42:57,000
Naturalment, dan mhux kollha li interessanti. X'jiġri jekk jien tixtieq li jkollha 2 istudenti?

795
00:42:57,000 --> 00:42:59,000
Li l-ebda big deal. I jistgħu jappoġġjaw 2 persuni.

796
00:42:59,000 --> 00:43:03,000
Let me imorru quddiem u jenfasizzaw dan u jinżlu hawn,

797
00:43:03,000 --> 00:43:09,000
u nista 'ngħid "id = 456" għal xi ħadd bħal Rob li jgħix fil Kirkland.

798
00:43:09,000 --> 00:43:12,000
>> Okay, stenna, iżda I ma jistgħux jikkontestaw dawn l-istess ħaġa,

799
00:43:12,000 --> 00:43:15,000
u jidher qisu jien ser ikollhom kopja dan,

800
00:43:15,000 --> 00:43:19,000
so let me ngħid li dawn se jkunu varjabbli David,

801
00:43:19,000 --> 00:43:23,000
u let me nikseb xi kopji ta 'dawn għall Rob.

802
00:43:23,000 --> 00:43:27,000
Aħna ser sejħa dawn Rob iżda dan mhuwiex sejjer jaħdem issa

803
00:43:27,000 --> 00:43:33,000
minħabba I-stenna, ejja bidla lili biex ID1, name1 u house1.

804
00:43:33,000 --> 00:43:35,000
Rob se jkun 2, 2.

805
00:43:35,000 --> 00:43:42,000
Stajt ltqajna biex tbiddel dan hawn, hawn, hawn, hawn, hawn, hawn.

806
00:43:42,000 --> 00:43:45,000
Stenna, dak dwar Tommy? Ejja nagħmlu dan mill-ġdid.

807
00:43:45,000 --> 00:43:49,000
Ovvjament jekk inti xorta taħseb li dan huwa mod tajjeb ta 'kif isir dan, mhuwiex,

808
00:43:49,000 --> 00:43:52,000
hekk kopja / paste ħażina.

809
00:43:52,000 --> 00:43:55,000
Iżda aħna solvuta din ġimgħa ilu.

810
00:43:55,000 --> 00:43:59,000
>> Liema kienet soluzzjoni tagħna meta ridna li jkollhom każi multipli tat-tip tad-data istess?

811
00:43:59,000 --> 00:44:01,000
[Studenti] Firxa.

812
00:44:01,000 --> 00:44:03,000
Firxa, so let me jippruvaw biex tnaddaf dan up.

813
00:44:03,000 --> 00:44:07,000
Let me jagħmlu xi spazju għall myself fil-quċċata, u let me minflok tagħmel dan hawn.

814
00:44:07,000 --> 00:44:12,000
Aħna ser sejħa dawn in-nies, u minflok jien se ngħid "ids int,"

815
00:44:12,000 --> 00:44:14,000
u jien ser tappoġġja 3 ta 'magħna għal issa.

816
00:44:14,000 --> 00:44:18,000
Jien se ngħid "ismijiet spag," u jien ser tappoġġa 3 ta 'magħna,

817
00:44:18,000 --> 00:44:22,000
u mbagħad jien se ngħid "djar spag," u jien ser tappoġġja 3 minna.

818
00:44:22,000 --> 00:44:26,000
Issa fil hawn minflok David jkollna varjazzjonijiet lokali tiegħu stess

819
00:44:26,000 --> 00:44:28,000
nistgħu jeħles dawk.

820
00:44:28,000 --> 00:44:30,000
Dan iħoss tajba li aħna qed tindif dan up.

821
00:44:30,000 --> 00:44:35,000
I jistgħu mbagħad ngħid David se tkun [0] u ismijiet [0]

822
00:44:35,000 --> 00:44:38,000
u djar [0].

823
00:44:38,000 --> 00:44:41,000
U allura Rob nistgħu istess mod jiffrankaw fuq dan.

824
00:44:41,000 --> 00:44:46,000
Ejja tpoġġi din stabbiliti hawn, hekk hu għaddej biex arbitrarjament tkun ids [1].

825
00:44:46,000 --> 00:44:50,000
Hu għaddej biex tkun l-ismijiet [1],

826
00:44:50,000 --> 00:44:53,000
u mbagħad fl-aħħar, djar [1].

827
00:44:53,000 --> 00:44:57,000
>> Still ftit tedious, u issa għandi din il-figura,

828
00:44:57,000 --> 00:45:03,000
hekk ejja ngħidu "ismijiet [0], id [0], djar [0],

829
00:45:03,000 --> 00:45:06,000
u ejja pluralize dan.

830
00:45:06,000 --> 00:45:09,000
IDs, ids, ids.

831
00:45:09,000 --> 00:45:12,000
U għal darb'oħra, jien tagħmel dan, sabiex għal darb'oħra, jien diġà jirrikorru għal kopja / paste mill-ġdid,

832
00:45:12,000 --> 00:45:14,000
hekk odds huma hemm soluzzjoni oħra hawn.

833
00:45:14,000 --> 00:45:18,000
I tista 'probabbilment tnaddaf dan up ulterjuri ma' linja jew xi ħaġa bħal dik,

834
00:45:18,000 --> 00:45:21,000
hekk fil-qosor, huwa ftit aħjar iżda xorta jħoss simili

835
00:45:21,000 --> 00:45:24,000
Jien jirrikorru kopja / paste, imma anki dan, I jsostnu,

836
00:45:24,000 --> 00:45:27,000
mhuwiex verament fundamentalment is-soluzzjoni dritt minħabba

837
00:45:27,000 --> 00:45:29,000
dak li jekk f'xi aħna tiddeċiedi inti taf liema?

838
00:45:29,000 --> 00:45:32,000
Aħna verament kellha ħażna indirizzi email għall David u Rob

839
00:45:32,000 --> 00:45:34,000
u kulħadd f'dan il-programm.

840
00:45:34,000 --> 00:45:36,000
Għandna wkoll taħżen numri tat-telefon.

841
00:45:36,000 --> 00:45:39,000
Għandna wkoll taħżen numri ta 'kuntatt ta' emerġenza.

842
00:45:39,000 --> 00:45:41,000
Aħna kollha dawn il-biċċiet ta 'data li rridu li jaħżen,

843
00:45:41,000 --> 00:45:43,000
hekk kif taħseb li tmur dwar kif isir dan?

844
00:45:43,000 --> 00:45:46,000
>> You jiddikjaraw ieħor array fil-quċċata, u allura inti manwalment żid

845
00:45:46,000 --> 00:45:49,000
l-indirizz email [0], indirizz elettroniku [1]

846
00:45:49,000 --> 00:45:51,000
għall David u Rob u oħrajn.

847
00:45:51,000 --> 00:45:56,000
Imma hemm verament biss suppożizzjoni sottostanti dan id-disinn

848
00:45:56,000 --> 00:45:59,000
li jiena jużaw is-sistema unur li tkun taf li

849
00:45:59,000 --> 00:46:03,000
[I] f'kull arrays diversi

850
00:46:03,000 --> 00:46:06,000
biss hekk jiġri li jirreferu għall-istess persuna,

851
00:46:06,000 --> 00:46:10,000
hekk [0] fil ids huwa numru 123,

852
00:46:10,000 --> 00:46:13,000
u jien ser jassumi li l-ismijiet [0]

853
00:46:13,000 --> 00:46:16,000
huwa l-isem l-istess persuna u djar [0]

854
00:46:16,000 --> 00:46:21,000
huwa d-dar l-istess persuna u ibqa 'sejjer hekk għall kollha tal-matriċi varji li I joħolqu.

855
00:46:21,000 --> 00:46:24,000
Iżda avviż li hemm l-ebda rabta fundamentali

856
00:46:24,000 --> 00:46:27,000
fost dawk il-biċċiet 3 ta 'informazzjoni, id-isem u d-dar,

857
00:46:27,000 --> 00:46:32,000
anke jekk l-entità aħna qed jippruvaw mudell f'dan il-programm ma jkunx matriċi.

858
00:46:32,000 --> 00:46:35,000
Arrays huma biss b'dan il-mod programmatiku biex dan isir.

859
00:46:35,000 --> 00:46:38,000
Dak li aħna verament irridu li mudell fil-programm tagħna huwa persuna

860
00:46:38,000 --> 00:46:41,000
bħal David, persuna bħal Rob minn ġewwa illi

861
00:46:41,000 --> 00:46:46,000
jew siġillar huwa isem u l-ID u dar.

862
00:46:46,000 --> 00:46:49,000
>> Nistgħu b'xi mod tesprimi din l-idea ta 'inkapsulament

863
00:46:49,000 --> 00:46:52,000
li bih persuna jkollha ID, isem u dar

864
00:46:52,000 --> 00:46:55,000
u mhux jirrikorru għal verament dan Hack biha aħna biss

865
00:46:55,000 --> 00:46:58,000
fiduċja li xi ħaġa kategorija

866
00:46:58,000 --> 00:47:02,000
jirreferi għall-entità tal-bniedem istess f'kull wieħed minn dawn arrays differenti?

867
00:47:02,000 --> 00:47:04,000
Nistgħu fil-fatt jagħmlu dan.

868
00:47:04,000 --> 00:47:08,000
Let me go fuq ewlenija għal issa, u let me toħloq stess tad-data tiegħi tip

869
00:47:08,000 --> 00:47:10,000
għall verament l-ewwel darba.

870
00:47:10,000 --> 00:47:14,000
Aħna użati din it-teknika fl-ġirja,

871
00:47:14,000 --> 00:47:17,000
iżda hawnhekk jien ser jimxi 'l quddiem u joħolqu tip ta' data,

872
00:47:17,000 --> 00:47:19,000
u inti taf liema, jien ser sejħa hija student jew persuna,

873
00:47:19,000 --> 00:47:23,000
u jien ser tuża typedef għal jiddefinixxu tip.

874
00:47:23,000 --> 00:47:25,000
Jien se ngħid li dan huwa l-istruttura,

875
00:47:25,000 --> 00:47:29,000
u allura din l-istruttura se tkun ta 'student tip, aħna ser ngħidu,

876
00:47:29,000 --> 00:47:31,000
anki jekk huwa ftit datata issa għalija.

877
00:47:31,000 --> 00:47:33,000
Aħna ser jgħidu "int id."

878
00:47:33,000 --> 00:47:35,000
Aħna ser jgħidu "isem sekwenza."

879
00:47:35,000 --> 00:47:37,000
Imbagħad aħna ser ngħidu "house string,"

880
00:47:37,000 --> 00:47:40,000
hekk issa sa l-aħħar ta 'dawn il-linji ftit tal-kodiċi

881
00:47:40,000 --> 00:47:45,000
I għadek mgħallma clang li jeżisti

882
00:47:45,000 --> 00:47:49,000
tip ta 'data minbarra ints, minbarra kordi, minbarra jirdoppja, minbarra flowts.

883
00:47:49,000 --> 00:47:54,000
>> Bħala ta 'dan il-mument fil-linja ħin 11, issa hemm tip ta' data ġdida msejħa l-istudenti,

884
00:47:54,000 --> 00:47:58,000
u issa nista 'niddikjara varjabbli student kullimkien nixtieq,

885
00:47:58,000 --> 00:48:01,000
so let me iscroll hawn biex in-nies.

886
00:48:01,000 --> 00:48:05,000
Issa nista 'teħles minn dan, u I tista' tmur lura għal David hawn,

887
00:48:05,000 --> 00:48:10,000
u għal David I jistgħu attwalment ngħid li David,

888
00:48:10,000 --> 00:48:13,000
nistgħu litteralment isem il-varjabbli wara myself,

889
00:48:13,000 --> 00:48:16,000
se tkun ta 'student tip.

890
00:48:16,000 --> 00:48:18,000
Dan jista 'tfittex ftit stramb, imma dan mhux kollha li differenti

891
00:48:18,000 --> 00:48:22,000
milli jiddikjaraw xi ħaġa bħala int jew string jew float.

892
00:48:22,000 --> 00:48:24,000
Huwa biss hekk jiġri li għandu jissejjaħ student issa,

893
00:48:24,000 --> 00:48:28,000
u jekk irrid biex xi ħaġa ġewwa ta 'din l-istruttura

894
00:48:28,000 --> 00:48:31,000
I issa għandhom jużaw biċċa ġdida ta 'sintassi, imma hija pjuttost sempliċi,

895
00:48:31,000 --> 00:48:39,000
david.id = 123, david.name = "David" fil-kapital D,

896
00:48:39,000 --> 00:48:42,000
u david.house = "Mather,"

897
00:48:42,000 --> 00:48:46,000
u issa nista 'teħles minn dan il-għalf hawn.

898
00:48:46,000 --> 00:48:51,000
Avviż konna issa ġġeddu programm tagħna verament mod ferm aħjar

899
00:48:51,000 --> 00:48:54,000
f'dak il-programm tagħna issa jirrifletti d-dinja reali.

900
00:48:54,000 --> 00:48:57,000
>> Hemm kunċett tad-dinja reali ta 'persuna jew student.

901
00:48:57,000 --> 00:49:02,000
Hawnhekk għandna issa verżjoni C ta 'persuna jew aktar speċifikament student.

902
00:49:02,000 --> 00:49:05,000
Ġewwa ta 'dik il-persuna huma dawn il-karatteristiċi relevanti,

903
00:49:05,000 --> 00:49:10,000
ID, l-isem u d-dar, u għalhekk Rob essenzjalment isir l-istess ħaġa stabbiliti hawn,

904
00:49:10,000 --> 00:49:14,000
hekk istudenti Rob, u issa rob.id = 456,

905
00:49:14,000 --> 00:49:17,000
rob.name = "Rob."

906
00:49:17,000 --> 00:49:20,000
Il-fatt li l-varjabbli hija msejħa Rob huwa tip ta 'sens.

907
00:49:20,000 --> 00:49:22,000
Nistgħu qalu li din x jew y jew z.

908
00:49:22,000 --> 00:49:25,000
Aħna biss imsemmija hija Rob jkun semantikament konsistenti,

909
00:49:25,000 --> 00:49:28,000
imma verament l-isem huwa ġewwa ta 'dak il-qasam innifsu,

910
00:49:28,000 --> 00:49:30,000
hekk issa għandi dan.

911
00:49:30,000 --> 00:49:33,000
Dan ukoll ma jħossu bħal l-aħjar disinn f'dak stajt iebes kodifikati David.

912
00:49:33,000 --> 00:49:35,000
Stajt iebes kodifikati Rob.

913
00:49:35,000 --> 00:49:39,000
U jien xorta jkollhom jirrikorru għal xi kopja u paste kull darba nixtieq varjabbli ġodda.

914
00:49:39,000 --> 00:49:43,000
Barra minn hekk, I għandhom apparentement jagħti lil kull wieħed dawn il-varjabbli l-isem,

915
00:49:43,000 --> 00:49:46,000
anki jekk I d ​​ħafna pjuttost jiddeskrivu dawn il-varjabbli

916
00:49:46,000 --> 00:49:48,000
 aktar studenti ġeneriku kif.

917
00:49:48,000 --> 00:49:52,000
>> Issa nistgħu jingħaqdu l-ideat li kienu qegħdin jaħdmu tajjeb għalina

918
00:49:52,000 --> 00:49:56,000
u minflok jgħidu, "Inti taf liema, jagħtu me istudenti imsejħa varjabbli,

919
00:49:56,000 --> 00:50:01,000
u ejja li hija tkun ta 'daqs 3, "hekk issa I jistgħu jirfinaw din ulterjuri,

920
00:50:01,000 --> 00:50:04,000
jeħles mill-David manwalment iddikjarat,

921
00:50:04,000 --> 00:50:08,000
u nista 'ngħid xi ħaġa simili minflok istudenti [0] hawn.

922
00:50:08,000 --> 00:50:11,000
I jistgħu mbagħad ngħid istudenti [0] hawn,

923
00:50:11,000 --> 00:50:14,000
istudenti [0] hawn, u oħrajn, u I tista 'tmur madwar

924
00:50:14,000 --> 00:50:16,000
u nadif li għall Rob.

925
00:50:16,000 --> 00:50:19,000
I tista 'wkoll tmur dwar issa forsi żżid linja

926
00:50:19,000 --> 00:50:23,000
u l-użu GetString u GetInt biex fil-fatt tikseb dawn il-valuri mill-utent.

927
00:50:23,000 --> 00:50:27,000
I tista 'tmur dwar żżid kostanti għaliex dan huwa ġeneralment prattika ħażina

928
00:50:27,000 --> 00:50:29,000
għall-kodiċi hard xi numru arbitrarju bħal 3 dritt hawn

929
00:50:29,000 --> 00:50:33,000
u mbagħad biss ftakar li inti għandek tpoġġi mhux aktar minn 3 istudenti fiha.

930
00:50:33,000 --> 00:50:36,000
Dan probabbilment ikun aħjar li tuża # tiddefinixxi fil-quċċata tal-fajl tiegħi

931
00:50:36,000 --> 00:50:40,000
u l-fattur li minn, hekk fil-fatt, let me imorru quddiem u jiġġeneralizza din.

932
00:50:40,000 --> 00:50:43,000
>> Let me jiftħu eżempju li l-fost lum

933
00:50:43,000 --> 00:50:46,000
eżempji bil-quddiem, structs1.

934
00:50:46,000 --> 00:50:49,000
Dan huwa programm aktar kompluta li juża # tiddefinixxi up here

935
00:50:49,000 --> 00:50:51,000
u jgħid aħna qed tmur biex ikollhom 3 istudenti fil-kontumaċja.

936
00:50:51,000 --> 00:50:54,000
Hawnhekk jien tiddikjara jiswew klassi ta 'studenti,

937
00:50:54,000 --> 00:50:57,000
hekk klassi ta 'studenti, u issa jien jużaw ħolqa

938
00:50:57,000 --> 00:51:00,000
biss biex jagħmlu l-kodiċi ftit aktar eleganti, timla l-klassi

939
00:51:00,000 --> 00:51:05,000
b'input-utent, hekk jtenni mill i = 0 sa l-istudenti, li huwa 3.

940
00:51:05,000 --> 00:51:07,000
U mbagħad I pront lill-utent f'dan il-verżjoni

941
00:51:07,000 --> 00:51:10,000
 x'hemm ID-istudent, u I ġġibu bil GetInt.

942
00:51:10,000 --> 00:51:13,000
X'hemm isem l-istudent, u mbagħad I ġġibu bil GetString.

943
00:51:13,000 --> 00:51:15,000
X'hemm dar l-istudent? I ġġibu bil GetString.

944
00:51:15,000 --> 00:51:19,000
U mbagħad fil-qiegħ hawnhekk I biss iddeċieda li jibdel

945
00:51:19,000 --> 00:51:22,000
kif jien istampar dawn jitwettqu u li attwalment jużaw linja,

946
00:51:22,000 --> 00:51:24,000
u li jien istampar?

947
00:51:24,000 --> 00:51:27,000
Skond il-kumment jien istampar xi ħadd fil Mather,

948
00:51:27,000 --> 00:51:30,000
u li hu hekk Rob u Tommy u oħrajn-fatt tal Tommy fil Mather.

949
00:51:30,000 --> 00:51:34,000
Tommy u David tkun stampata f'dan il-każ, imma kif qed taħdem din?

950
00:51:34,000 --> 00:51:40,000
Aħna ma bbenefikawx din il-funzjoni qabel, iżda tieħu raden dwar dak li dan ma.

951
00:51:40,000 --> 00:51:42,000
Tqabbel kordi.

952
00:51:42,000 --> 00:51:45,000
>> Huwa ftit mhux ovvju kif jikkompara kordi għaliex jirriżulta

953
00:51:45,000 --> 00:51:49,000
jekk dan jirritorna 0 li tfisser il-kordi huma ugwali.

954
00:51:49,000 --> 00:51:53,000
Jekk dan jirritorna a -1 li jfisser wieħed jidħol alfabetikament qabel l-oħra,

955
00:51:53,000 --> 00:51:57,000
u jekk dan jirritorna 1 li tfisser il-kelma oħra tkun ġejja alfabetikament

956
00:51:57,000 --> 00:52:00,000
qabel l-ieħor, u inti tista 'tfittex online jew fil-paġna bniedem

957
00:52:00,000 --> 00:52:04,000
li jaraw eżattament liema mod huwa li, iżda dan kollu issa qed tagħmel huwa huwa qal

958
00:52:04,000 --> 00:52:09,000
jekk l-[i]. dar hija ugwali għal "Mather"

959
00:52:09,000 --> 00:52:13,000
imbagħad imorru quddiem u jistampa hekk u hekk huwa fil Mather.

960
00:52:13,000 --> 00:52:16,000
Iżda hawn xi ħaġa li aħna ma bbenefikawx qabel, u aħna ser terga 'lura għal dan.

961
00:52:16,000 --> 00:52:21,000
I do not recall qatt li jiġri dan fi kwalunkwe ta 'programmi tiegħi.

962
00:52:21,000 --> 00:52:24,000
Free jidher li qed jirreferi għall-memorja, ħelsien memorja,

963
00:52:24,000 --> 00:52:31,000
imma dak memorja jien apparentement ħelsien f'dan loop fil-qiegħ ta 'dan il-programm?

964
00:52:31,000 --> 00:52:34,000
Jidher qisu jien ħelsien isem ta 'persuna

965
00:52:34,000 --> 00:52:37,000
u d-dar ta 'persuna, iżda għaliex huwa li?

966
00:52:37,000 --> 00:52:41,000
>> Jirriżulta kollha dawn il-ġimgħat li inti kont qed tuża GetString

967
00:52:41,000 --> 00:52:45,000
konna tip ta 'qegħdin jintroduċu bug fis-kull wieħed mill-programmi tiegħek.

968
00:52:45,000 --> 00:52:51,000
GetString mill-memorja jalloka disinn sabiex ikun jista 'ritorn lejn inti string,

969
00:52:51,000 --> 00:52:55,000
bħal David, jew Rob, u inti tista 'mbagħad tagħmel xi trid

970
00:52:55,000 --> 00:52:59,000
ma 'dak string fil-programm tiegħek għax konna riżervati l-memorja għalik.

971
00:52:59,000 --> 00:53:02,000
Il-problema hija dan kollu ħin kull darba li inti sejħa GetString

972
00:53:02,000 --> 00:53:05,000
aħna, l-awturi ta GetString, ġew tistaqsi s-sistema operattiva

973
00:53:05,000 --> 00:53:07,000
biex tagħtina ftit ta 'RAM għal dan sekwenza.

974
00:53:07,000 --> 00:53:09,000
Agħtina daqsxejn ta 'RAM għal dan sekwenza li jmiss.

975
00:53:09,000 --> 00:53:11,000
Agħtina RAM ftit aktar għal din is-sekwenza li jmiss.

976
00:53:11,000 --> 00:53:13,000
Dak li inti, il-programmer, qatt ma kienu jagħmlu

977
00:53:13,000 --> 00:53:15,000
qed tagħti lilna li back-memorja,

978
00:53:15,000 --> 00:53:17,000
hekk għal dawn il-ġimgħat diversi kollha tal-programmi li inti stajt bil-miktub

979
00:53:17,000 --> 00:53:20,000
kellhom dak li sejjaħ qabża memorja fejn iżommu jużaw

980
00:53:20,000 --> 00:53:24,000
memorja aktar u aktar kull darba li inti sejħa GetString, u li l-multa.

981
00:53:24,000 --> 00:53:27,000
We deliberatament jagħmlu dan fl-ewwel ġimgħat għaliex mhuwiex dak interessanti

982
00:53:27,000 --> 00:53:29,000
li jkollhom għalfejn tinkwieta dwar fejn il-sekwenza ikun ġej minn.

983
00:53:29,000 --> 00:53:34,000
Kulma trid hija l-kelma Rob li jiġu lura meta l-utent tipi huwa pulzieri

984
00:53:34,000 --> 00:53:38,000
>> Iżda miexja 'l quddiem issa għandna biex jibda jkollna aktar sofistikati dwar dan.

985
00:53:38,000 --> 00:53:42,000
Kull darba li aħna jallokaw memorja aħna aħjar eventwalment jagħtih lura.

986
00:53:42,000 --> 00:53:45,000
Mod ieħor fl-dinja reali fuq Mac tiegħek jew PC inti jista 'jkollhom xi kultant esperjenza

987
00:53:45,000 --> 00:53:50,000
Sintomi fejn il-kompjuter tiegħek huwa tħin biex jieqaf eventwalment

988
00:53:50,000 --> 00:53:54,000
jew l-ballun stupid bajja għażil huwa biss jokkupa l-infurmatika

989
00:53:54,000 --> 00:53:56,000
attenzjoni sħiħa u inti ma tistax tagħmel affarijiet.

990
00:53:56,000 --> 00:54:00,000
Dan jista 'jiġi spjegat minn kull numru ta' bugs, imma fost dawk bugs possibbli

991
00:54:00,000 --> 00:54:03,000
huma affarijiet msejħa tnixxijiet memorja fejn xi ħadd li kiteb li l-biċċa ta 'softwer

992
00:54:03,000 --> 00:54:07,000
inti qed tuża ma ftakar biex memorja ħielsa

993
00:54:07,000 --> 00:54:10,000
li hu jew hi talbet lill-sistema operattiva għal,

994
00:54:10,000 --> 00:54:14,000
ma jużawx GetString, għaliex li l-ħaġa CS50, iżda bl-użu funzjonijiet simili

995
00:54:14,000 --> 00:54:16,000
li titlob lill-sistema operattiva għall-memorja.

996
00:54:16,000 --> 00:54:19,000
Jekk inti jew li screw up u qatt fil-fatt ritorn li l-memorja

997
00:54:19,000 --> 00:54:24,000
sintomu ta 'li jista' jkun li programm inaqqas u jrażżan u tnaqqas ir-ritmu

998
00:54:24,000 --> 00:54:26,000
sakemm inti tiftakar li sejħa ħielsa.

999
00:54:26,000 --> 00:54:28,000
>> Aħna ser terga 'lura għal meta u għaliex inti kieku ssejjaħ ħielsa,

1000
00:54:28,000 --> 00:54:32,000
imma ejja imorru quddiem biss għal miżura tajba u tipprova taħdem dan il-programm partikolari.

1001
00:54:32,000 --> 00:54:35,000
Dan kien jissejjaħ structs1, jidħol.

1002
00:54:35,000 --> 00:54:40,000
Let me imorru quddiem u run structs1, 123, David Mather,

1003
00:54:40,000 --> 00:54:47,000
456, Rob Kirkland, 789,

1004
00:54:47,000 --> 00:54:50,000
Tommy Mather, u naraw David fil Mather, tal Tommy fil Mather.

1005
00:54:50,000 --> 00:54:53,000
Dan huwa biss verifika sanità ftit li l-programm qed taħdem.

1006
00:54:53,000 --> 00:54:56,000
Issa, sfortunatament, dan il-programm huwa xi ftit frustranti f'dik

1007
00:54:56,000 --> 00:55:00,000
I ma dak kollu li jaħdmu, I ittajpjat fil 9 kordi differenti, hit jidħol,

1008
00:55:00,000 --> 00:55:04,000
kien qal li kien fil Mather, għadhom ovvjament kont naf li kien Mather diġà minħabba I ittajpjat.

1009
00:55:04,000 --> 00:55:07,000
Ikun inqas sbieħ jekk dan il-programm huwa aktar simili database

1010
00:55:07,000 --> 00:55:10,000
u huwa attwalment jiftakar dak I ittajpjat fil-

1011
00:55:10,000 --> 00:55:12,000
so I qatt jerġa 'jkollhom kontribut dawn ir-reġistri istudent.

1012
00:55:12,000 --> 00:55:15,000
Forsi huwa bħal sistema registrarial.

1013
00:55:15,000 --> 00:55:21,000
>> Nistgħu nagħmlu dan bl-użu din it-teknika magħrufa bħala input fajl fajl I / O, u l-produzzjoni,

1014
00:55:21,000 --> 00:55:24,000
mod ħafna ġeneriku ta 'tgħid kwalunkwe ħin li inti tixtieq li jaqra fajls jew ikteb fajls

1015
00:55:24,000 --> 00:55:26,000
inti tista 'tagħmel dan ma' sett ta 'funzjonijiet.

1016
00:55:26,000 --> 00:55:29,000
Let me imorru quddiem u tiftaħ din structs2.c eżempju,

1017
00:55:29,000 --> 00:55:33,000
li huwa kważi identiku, imma ejja ara dak li issa ma.

1018
00:55:33,000 --> 00:55:36,000
Fil-quċċata tal-fajl Niddikjara klassi ta 'studenti.

1019
00:55:36,000 --> 00:55:38,000
I imbagħad timla l-klassi b'input l-utent,

1020
00:55:38,000 --> 00:55:41,000
hekk dawk il-linji ta 'kodiċi huma eżattament bħal qabel.

1021
00:55:41,000 --> 00:55:45,000
Imbagħad jekk I iscroll stabbiliti hawn I jistampaw kull min huwa fil Mather arbitrarjament bħal qabel,

1022
00:55:45,000 --> 00:55:47,000
iżda din hija karatteristika ġdida interessanti.

1023
00:55:47,000 --> 00:55:51,000
Dawn il-linji ta 'kodiċi huma ġodda, u dawn jintroduċu xi ħaġa hawn,

1024
00:55:51,000 --> 00:55:55,000
FAJL, l-għotjien, u li għandha * fil hawnhekk ukoll.

1025
00:55:55,000 --> 00:55:58,000
Let me jimxu dan hawn fuq, a * aktar minn hawnhekk ukoll.

1026
00:55:58,000 --> 00:56:00,000
>> Din il-funzjoni ma rajniex qabel, fopen,

1027
00:56:00,000 --> 00:56:03,000
iżda dan ifisser fajl miftuħ, so ejja skim permezz ta 'dawn,

1028
00:56:03,000 --> 00:56:05,000
u din hija xi ħaġa aħna ser terga 'lura fl psets futuri,

1029
00:56:05,000 --> 00:56:10,000
iżda din il-linja hawnhekk essenzjalment jiftaħ fajl imsejjaħ database,

1030
00:56:10,000 --> 00:56:13,000
u dan b'mod speċifiku tiftħu b'tali mod li tista 'tagħmel dak li dan?

1031
00:56:13,000 --> 00:56:15,000
[Inaudible-istudent]

1032
00:56:15,000 --> 00:56:19,000
Dritt, hekk "w" ifisser biss huwa javżak-sistema operattiva

1033
00:56:19,000 --> 00:56:21,000
tiftaħ dan il-fajl b'tali mod li nista 'tikteb lilha.

1034
00:56:21,000 --> 00:56:23,000
Ma rridx biex taqraha. Ma rridx li biss ħarsa lejn dan.

1035
00:56:23,000 --> 00:56:26,000
Irrid li jibdlu u żid Jittieħed potenzjalment miegħu,

1036
00:56:26,000 --> 00:56:28,000
u l-fajl se jiġu msejħa database.

1037
00:56:28,000 --> 00:56:30,000
Dan jista 'jissejjaħ xejn.

1038
00:56:30,000 --> 00:56:32,000
Dan jista 'jkun database.txt. Dan jista 'jkun. Db.

1039
00:56:32,000 --> 00:56:37,000
Dan jista 'jkun kelma bħal foo, iżda I għażlet arbitrarjament li l-isem tad-database fajl.

1040
00:56:37,000 --> 00:56:42,000
Dan huwa kontroll sanità ftit li aħna ser terga 'lura għal f'dettall kbir matul iż-żmien,

1041
00:56:42,000 --> 00:56:47,000
jekk fp, għal pointer fajl, ma NULL ugwali li tfisser kollox huwa tajjeb.

1042
00:56:47,000 --> 00:56:51,000
>> Long storja qasira, funzjonijiet simili fopen kultant jonqsu.

1043
00:56:51,000 --> 00:56:53,000
Forsi l-fajl ma teżistix. Forsi int minn spazju diska.

1044
00:56:53,000 --> 00:56:55,000
Forsi inti ma għandekx permess biex dak folder,

1045
00:56:55,000 --> 00:56:58,000
hekk jekk fopen jirritorna xi ħaġa null ħażina ġara.

1046
00:56:58,000 --> 00:57:02,000
Bil-maqlub, jekk fopen ma ritorn null kollox huwa tajjeb

1047
00:57:02,000 --> 00:57:04,000
u I tista 'tibda bil-miktub lill dan il-fajl.

1048
00:57:04,000 --> 00:57:06,000
Hawn trick ġdid.

1049
00:57:06,000 --> 00:57:08,000
Din hija linja għal li l-iterazzjoni fuq kull wieħed mill-istudenti tiegħi,

1050
00:57:08,000 --> 00:57:10,000
u dan jistenna hekk simili għal dak li aħna ghamilt qabel,

1051
00:57:10,000 --> 00:57:15,000
iżda din il-funzjoni huwa kuġin ta printf sejjaħ fprintf għall-fajl printf,

1052
00:57:15,000 --> 00:57:18,000
u avviż huwa differenti biss 2 modi.

1053
00:57:18,000 --> 00:57:20,000
Wieħed, li jibda bil f minflok p,

1054
00:57:20,000 --> 00:57:23,000
iżda mbagħad ewwel argument tagħha hija apparentement liema?

1055
00:57:23,000 --> 00:57:25,000
[Studenti] File. >> Huwa fajl.

1056
00:57:25,000 --> 00:57:30,000
Din ħaġa imsejħa FP, li aħna ser eventwalment tease apparti dak pointer fajl huwa,

1057
00:57:30,000 --> 00:57:35,000
iżda għal issa fp sempliċement tirrappreżenta l-fajl li jien miftuħa,

1058
00:57:35,000 --> 00:57:41,000
hekk fprintf hawn huwa qal tipprintja ID dan l-utent għall-fajl, li ma l-iskrin.

1059
00:57:41,000 --> 00:57:44,000
Stampa isem l-utent għall-fajl, li ma l-iskrin,

1060
00:57:44,000 --> 00:57:47,000
l-dar għall-fajl, li ma l-iskrin, u mbagħad stabbiliti hawn, ovvjament,

1061
00:57:47,000 --> 00:57:50,000
jagħlaq il-fajl, u mbagħad stabbiliti hawn b'xejn l-memorja.

1062
00:57:50,000 --> 00:57:53,000
>> L-unika differenza bejn din il-verżjoni 2 u verżjoni 1

1063
00:57:53,000 --> 00:57:58,000
hija l-introduzzjoni ta 'fopen u dan FAJL ma *

1064
00:57:58,000 --> 00:58:01,000
u dan il-kunċett ta 'fprintf, so ejja ara dak ir-riżultat aħħari huwa.

1065
00:58:01,000 --> 00:58:03,000
Let me go fis tieqa terminal tiegħi.

1066
00:58:03,000 --> 00:58:06,000
Let me run structs2, jidħol.

1067
00:58:06,000 --> 00:58:09,000
Id-Dehra kollox huwa tajjeb. Ejja terġa 'ssir structs2.

1068
00:58:09,000 --> 00:58:15,000
123, David Mather, 456, Rob Kirkland,

1069
00:58:15,000 --> 00:58:19,000
789, Tommy Mather, jidħol.

1070
00:58:19,000 --> 00:58:23,000
Qisu ruħu l-istess, imma jekk jien issa do ls

1071
00:58:23,000 --> 00:58:28,000
Avviż dak fajl huwa hawnhekk fost l-kodiċi tiegħi, id-database,

1072
00:58:28,000 --> 00:58:32,000
hekk ejja miftuħa li, gedit ta 'database, u ħarsa lejn dak.

1073
00:58:32,000 --> 00:58:34,000
Mhuwiex l-sexiest ta 'formats tal-fajls.

1074
00:58:34,000 --> 00:58:38,000
Huwa verament huwa biċċa waħda ta 'linja data għal kull ringiela għal kull linja,

1075
00:58:38,000 --> 00:58:42,000
imma dawk fostkom li jużaw fajls Excel jew CSV, comma separati valuri,

1076
00:58:42,000 --> 00:58:47,000
I jista 'ċertament użaw fprintf biex minflok forsi jagħmlu xi ħaġa bħal din

1077
00:58:47,000 --> 00:58:50,000
hekk li I jistgħu attwalment joħolqu l-ekwivalenti ta 'fajl Excel

1078
00:58:50,000 --> 00:58:53,000
billi tissepara l-affarijiet ma virgoli, mhux biss linji ġodda.

1079
00:58:53,000 --> 00:58:56,000
>> F'dan il-każ jekk kelli minflok tintuża virgoli minflok linji ġodda

1080
00:58:56,000 --> 00:59:01,000
I jistgħu litteralment tiftaħ dan il-fajl database fl-Excel jekk I minflok għamilha teżamina bħal dan.

1081
00:59:01,000 --> 00:59:03,000
Fil-qosor, issa li għandna l-poter li tikteb fajls

1082
00:59:03,000 --> 00:59:07,000
aħna issa tista 'tibda data persistenti, iż-żamma madwar fuq diska

1083
00:59:07,000 --> 00:59:10,000
sabiex inkunu nistgħu nżommu l-informazzjoni madwar darb'oħra u għal darb'oħra.

1084
00:59:10,000 --> 00:59:14,000
Avviż ftit affarijiet oħra li huma issa ftit aktar familjari.

1085
00:59:14,000 --> 00:59:16,000
Fil-quċċata ta 'dan il-fajl C għandna typedef

1086
00:59:16,000 --> 00:59:21,000
għaliex ridna li jinħoloq tip ta 'data li jirrappreżenta kelma,

1087
00:59:21,000 --> 00:59:25,000
għalhekk dan it-tip huwa msejjaħ kelma, u ġewwa ta 'din l-istruttura

1088
00:59:25,000 --> 00:59:27,000
huwa ftit fancier issa.

1089
00:59:27,000 --> 00:59:30,000
Għaliex hija kelma magħmula minn apparentement firxa?

1090
00:59:30,000 --> 00:59:33,000
X'inhu kelma biss intuwittivament?

1091
00:59:33,000 --> 00:59:35,000
>> Huwa ta 'firxa ta' karattri.

1092
00:59:35,000 --> 00:59:37,000
Huwa sekwenza ta 'karattri lura lura lura.

1093
00:59:37,000 --> 00:59:41,000
ITTRI kollha caps jiġri li jkun we arbitrarjament ngħidu l-ikbar tul

1094
00:59:41,000 --> 00:59:44,000
ta 'xi kelma fid-dizzjunarju li aħna qed jużaw għall-ġirja.

1095
00:59:44,000 --> 00:59:46,000
Għaliex għandi 1?

1096
00:59:46,000 --> 00:59:48,000
Il null karattru.

1097
00:59:48,000 --> 00:59:51,000
Recall meta għamilna l-eżempju Bananagrams għandna bżonn valur speċjali

1098
00:59:51,000 --> 00:59:55,000
fl-aħħar tal-kelma sabiex iżżomm kont

1099
00:59:55,000 --> 00:59:59,000
ta 'fejn il-kliem fil-fatt spiċċat, u bħala l-ispeċifikazzjoni sett problema jgħid

1100
00:59:59,000 --> 01:00:03,000
hawn aħna qed jassoċjaw mal-kelma mogħtija valur Boolean,

1101
01:00:03,000 --> 01:00:05,000
bandiera, biex ngħidu hekk, vera jew falza.

1102
01:00:05,000 --> 01:00:09,000
Sibtha din il-kelma diġà, għaliex aħna realizzata

1103
01:00:09,000 --> 01:00:13,000
aħna verament jeħtieġu mod ta 'ftakar mhux biss dak kelma hija fil ġirja

1104
01:00:13,000 --> 01:00:15,000
iżda jekk jew le inti, il-bniedem, sabuha

1105
01:00:15,000 --> 01:00:20,000
b'tali mod li jekk inti ssib il-kelma "il-" inti tista 'mhux biss tip-, jidħlu, fil, jidħlu, il-jidħol

1106
01:00:20,000 --> 01:00:23,000
u jiksbu 3 punti, 3 punti, 3 punti, 3 punti.

1107
01:00:23,000 --> 01:00:26,000
Aħna rridu li tkun tista 'blacklist din il-kelma billi tistabbilixxi bool

1108
01:00:26,000 --> 01:00:29,000
li minnu jekk inti stajt diġà sabet li, u għalhekk huwa għalhekk li għandna

1109
01:00:29,000 --> 01:00:31,000
inkapsulati li f'din l-istruttura.

1110
01:00:31,000 --> 01:00:35,000
>> Issa, stabbiliti hawn fil ġirja hemm dan Struct oħra msejħa dizzjunarju.

1111
01:00:35,000 --> 01:00:39,000
Assenti hawnhekk hija l-kelma typedef għaliex f'dan il-każ

1112
01:00:39,000 --> 01:00:43,000
aħna meħtieġa biex jirrappreżentaw l-idea ta 'dizzjunarju,

1113
01:00:43,000 --> 01:00:46,000
u dizzjunarju fih mazz sħiħ ta 'kliem,

1114
01:00:46,000 --> 01:00:49,000
kif implikat minn din array, u kemm ta 'dawk il-kliem huma hemmhekk?

1115
01:00:49,000 --> 01:00:51,000
Ukoll, tkun xi tkun dan id-daqs varjabbli imsejħa jgħid.

1116
01:00:51,000 --> 01:00:53,000
Iżda aħna biss bżonn waħda dizzjunarju.

1117
01:00:53,000 --> 01:00:55,000
Aħna ma bżonn ta 'tip ta' data msejħa dizzjunarju.

1118
01:00:55,000 --> 01:00:58,000
Aħna biss bżonn waħda minnhom, u għalhekk jirriżulta fi C

1119
01:00:58,000 --> 01:01:03,000
li jekk inti ma jgħidux typedef, inti biss jgħidu Struct, allura ġewwa l-ċineg kaboċċi

1120
01:01:03,000 --> 01:01:05,000
inti tpoġġi varjabbli tiegħek, allura inti tpoġġi l-isem.

1121
01:01:05,000 --> 01:01:09,000
Dan huwa ddikjarat 1 dizzjunarju varjabbli imsejjaħ

1122
01:01:09,000 --> 01:01:11,000
li tidher bħal dan.

1123
01:01:11,000 --> 01:01:16,000
B'kuntrast, dawn il-linji qed joħolqu struttura tad-data li jistgħu jerġgħu jintużaw imsejjaħ kelma

1124
01:01:16,000 --> 01:01:19,000
inti tista 'toħloq kopji multipli ta', bħad ħloqna

1125
01:01:19,000 --> 01:01:22,000
kopji multipli ta 'studenti.

1126
01:01:22,000 --> 01:01:24,000
>> Xi jfisser dan finalment inessu li jagħmlu?

1127
01:01:24,000 --> 01:01:30,000
Let me go lura fil, ejja ngħidu, eżempju sempliċi minn żminijiet aktar sempliċi,

1128
01:01:30,000 --> 01:01:34,000
u let me jiftħu, ejja ngħidu, compare1.c.

1129
01:01:34,000 --> 01:01:38,000
Il-problema hawnhekk fil-idejn huwa li attwalment qoxra lura

1130
01:01:38,000 --> 01:01:41,000
is-saff ta 'spag u tibda tieħu off dawn ir-roti ta' taħriġ

1131
01:01:41,000 --> 01:01:44,000
għaliex jirriżulta li string dan il-ħin

1132
01:01:44,000 --> 01:01:47,000
huwa kif aħna imwiegħed fil-ġimgħa 1 verament ftit laqam,

1133
01:01:47,000 --> 01:01:51,000
sinonimu mill-bibljoteka CS50 għal xi ħaġa li jistenna ftit aktar cryptic,

1134
01:01:51,000 --> 01:01:53,000
* char, u Rajna dan il stilla qabel.

1135
01:01:53,000 --> 01:01:55,000
Aħna raw dan fil-kuntest ta 'fajls.

1136
01:01:55,000 --> 01:01:59,000
>> Ejja issa tara għaliex aħna kont qed jistaħbew dan id-dettall għal xi żmien issa.

1137
01:01:59,000 --> 01:02:02,000
Hawnhekk huwa fajl imsejjaħ compare1.c,

1138
01:02:02,000 --> 01:02:07,000
u apparentement jitlob lill-utent għal 2 kordi, su t,

1139
01:02:07,000 --> 01:02:11,000
u mbagħad tipprova tqabbel dawk kordi għall-ugwaljanza fil-linja 26,

1140
01:02:11,000 --> 01:02:14,000
u jekk dawn qed ugwali jgħid, "Inti ttajpjati l-istess ħaġa,"

1141
01:02:14,000 --> 01:02:17,000
u jekk dawn mhux qed ugwali jgħid, "Inti ittajpjat affarijiet differenti."

1142
01:02:17,000 --> 01:02:19,000
Let me imorru quddiem u jitmexxa dan il-programm.

1143
01:02:19,000 --> 01:02:23,000
Let me go fis direttorju sors tiegħi, tagħmel compare1. Hija miġbura okay.

1144
01:02:23,000 --> 01:02:25,000
Let me run compare1.

1145
01:02:25,000 --> 01:02:27,000
I ser zoom, jidħol.

1146
01:02:27,000 --> 01:02:29,000
Ngħid xi ħaġa. HELLO.

1147
01:02:29,000 --> 01:02:32,000
I ser ngħid xi ħaġa mill-ġdid. HELLO.

1148
01:02:32,000 --> 01:02:34,000
I definitely ma tip affarijiet differenti.

1149
01:02:34,000 --> 01:02:37,000
>> Let me tipprova dan mill-ġdid. BYE BYE.

1150
01:02:37,000 --> 01:02:40,000
Żgur li le differenti, hekk x'inhu għaddej hawn?

1151
01:02:40,000 --> 01:02:44,000
Ukoll, dak li hu verament jiġu pparagunati fil-linja 26?

1152
01:02:44,000 --> 01:02:46,000
[Inaudible-istudent]

1153
01:02:46,000 --> 01:02:49,000
Iva, hekk jirriżulta li string, data tat-tip, huwa tip ta 'gidba abjad.

1154
01:02:49,000 --> 01:02:53,000
A sensiela hija * char, imma dak huwa * char?

1155
01:02:53,000 --> 01:02:56,000
A * char, kif jgħidu, hija pointer,

1156
01:02:56,000 --> 01:03:00,000
u werrej huwa effettivament l-indirizz,

1157
01:03:00,000 --> 01:03:05,000
post somma fil-memorja, u jekk jiġri li għandek ittajpjat fil-kelma bħall HELLO,

1158
01:03:05,000 --> 01:03:08,000
jitlob lura mingħandhom il diskussjonijiet tal-passat ta 'spag

1159
01:03:08,000 --> 01:03:16,000
dan huwa bħall-kelma HELLO.

1160
01:03:16,000 --> 01:03:19,000
Ftakar li kelma bħal HELLO jistax jiġi rappreżentat

1161
01:03:19,000 --> 01:03:22,000
bħala firxa ta 'karattri bħal dan

1162
01:03:22,000 --> 01:03:25,000
u mbagħad ma 'karattru speċjali fit-tmiem imsejjaħ il-karattru null,

1163
01:03:25,000 --> 01:03:27,000
bħala l-ifisser, \.

1164
01:03:27,000 --> 01:03:29,000
X'inhu attwalment string?

1165
01:03:29,000 --> 01:03:32,000
Avviż li dan huwa biċċiet multipli ta 'memorja,

1166
01:03:32,000 --> 01:03:36,000
u fil-fatt, l-aħħar ta 'dan huwa magħruf biss ladarba inti tfittex permezz-sekwenza sħiħa

1167
01:03:36,000 --> 01:03:38,000
tfittex għall-karattru null speċjali.

1168
01:03:38,000 --> 01:03:41,000
Imma jekk dan huwa blokki ta 'memorja mill-memorja tal-kompjuter tiegħi,

1169
01:03:41,000 --> 01:03:44,000
ejja arbitrarju ngħid li dan string biss ltqajna xxurtjati,

1170
01:03:44,000 --> 01:03:47,000
u li ltqajna mqiegħda fil-bidu nett ta 'RAM kompjuter tiegħi.

1171
01:03:47,000 --> 01:03:54,000
Dan huwa byte 0, 1, 2, 3, 4, 5, 6 ...

1172
01:03:54,000 --> 01:04:02,000
>> Meta ngħid xi ħaġa simili GetString u nagħmel string s = GetString

1173
01:04:02,000 --> 01:04:04,000
dak li verament ikunu ritornati?

1174
01:04:04,000 --> 01:04:08,000
Għal dawn il-ġimgħat aħħar diversi, dak li verament qed maħżuna s

1175
01:04:08,000 --> 01:04:13,000
mhux din is-sekwenza per se, imma f'dan il-każ dak li qed jinħażen huwa

1176
01:04:13,000 --> 01:04:18,000
n-numru 0 għaliex dak GetString attwalment ma

1177
01:04:18,000 --> 01:04:20,000
huwa ma fiżikament ritorn string.

1178
01:04:20,000 --> 01:04:22,000
Dan lanqas ma verament jagħmel sens kunċettwali.

1179
01:04:22,000 --> 01:04:24,000
Dak li dan ritorn huwa numru.

1180
01:04:24,000 --> 01:04:28,000
Dak in-numru huwa l-indirizz ta 'HELLO fil-memorja,

1181
01:04:28,000 --> 01:04:32,000
u spag i mbagħad, jekk irridu qoxra lura dan is-saff, spag ma verament jeżistu.

1182
01:04:32,000 --> 01:04:35,000
Huwa biss simplifikazzjoni fil-librerija CS50.

1183
01:04:35,000 --> 01:04:38,000
>> Dan verament hija xi ħaġa imsejħa * char.

1184
01:04:38,000 --> 01:04:41,000
Char jagħmel sens għaliex x'hemm ftit kliem, bħal HELLO?

1185
01:04:41,000 --> 01:04:44,000
Ukoll, huwa sensiela ta 'Chars, serje ta' karattri.

1186
01:04:44,000 --> 01:04:47,000
* Char tfisser l-indirizz ta 'karattru,

1187
01:04:47,000 --> 01:04:50,000
hekk dak ma jfisser li jirritornaw string?

1188
01:04:50,000 --> 01:04:53,000
A sbieħ, mod sempliċi ta 'ritorn string

1189
01:04:53,000 --> 01:04:57,000
huwa pjuttost milli jippruvaw biex insemmu kif I-ritorn għal 5 jew 6 bytes differenti

1190
01:04:57,000 --> 01:05:01,000
let me lura fl-indirizz li byte?

1191
01:05:01,000 --> 01:05:03,000
L-ewwel waħda.

1192
01:05:03,000 --> 01:05:06,000
Fi kliem ieħor, let me jagħtuk l-indirizz ta 'karattru fil-memorja.

1193
01:05:06,000 --> 01:05:10,000
Dak hu * char tirrappreżenta, l-indirizz ta 'wieħed karattru wieħed fil-memorja.

1194
01:05:10,000 --> 01:05:12,000
Sejħa li s varjabbli.

1195
01:05:12,000 --> 01:05:15,000
Aħżen fil-i li jindirizzaw b'mod partikolari, li jiena arbitrarju qal huwa 0,

1196
01:05:15,000 --> 01:05:19,000
biss li żżomm affarijiet sempliċi, iżda fir-realtà huwa ġeneralment ta 'numru akbar.

1197
01:05:19,000 --> 01:05:21,000
>> Stenna minuta.

1198
01:05:21,000 --> 01:05:23,000
Jekk int biss tagħti me l-indirizz ta 'l-ewwel karattru, kif inkun naf x'inhi l-indirizz huwa

1199
01:05:23,000 --> 01:05:25,000
tal-karattru tieni, it-tielet, ir-raba 'u l-ħames?

1200
01:05:25,000 --> 01:05:27,000
[Inaudible-istudent]

1201
01:05:27,000 --> 01:05:31,000
Inti biss taf fejn it-tmiem tas-sekwenza huwa permezz ta 'dan trick handy,

1202
01:05:31,000 --> 01:05:35,000
hekk meta tuża xi ħaġa simili printf, liema printf litteralment tieħu bħala argument tagħha,

1203
01:05:35,000 --> 01:05:39,000
ifakkar li nużaw placeholder din% s, u allura inti jgħaddu

1204
01:05:39,000 --> 01:05:41,000
il-varjabbli li l-ħażna string.

1205
01:05:41,000 --> 01:05:47,000
Dak li int verament tgħaddi huwa l-indirizz ta 'l-ewwel karattru ta' dak sekwenza.

1206
01:05:47,000 --> 01:05:50,000
Printf mbagħad juża għal loop jew loop waqt malli jirċievi dik l-indirizz,

1207
01:05:50,000 --> 01:05:53,000
per eżempju, 0, so let me tagħmel dan issa,

1208
01:05:53,000 --> 01:06:02,000
printf ("% s \ n", i);

1209
01:06:02,000 --> 01:06:07,000
Meta I call printf ("% s \ n", i); dak li jien verament jipprovdu printf ma

1210
01:06:07,000 --> 01:06:13,000
huwa l-indirizz ta 'l-ewwel karattru fl-i, li f'dan il-każ arbitrarja huwa H.

1211
01:06:13,000 --> 01:06:16,000
>> Kif ma printf jafu eżattament dak li juri fuq l-iskrin?

1212
01:06:16,000 --> 01:06:19,000
Il-persuna li implimentat printf implimentata loop waqt jew għall loop

1213
01:06:19,000 --> 01:06:23,000
li tgħid ma dan il-karattru daqs il-karattru null speċjali?

1214
01:06:23,000 --> 01:06:25,000
Jekk le, jistampaw. Kif dwar dan wieħed?

1215
01:06:25,000 --> 01:06:28,000
Jekk le jistampaw, jistampaw, jistampaw, jistampaw.

1216
01:06:28,000 --> 01:06:32,000
Oh, dan huwa wieħed speċjali. Waqqaf istampar u r-ritorn għall-utent.

1217
01:06:32,000 --> 01:06:35,000
U li litteralment dak kollu li kien jiġri taħt il-barnuża,

1218
01:06:35,000 --> 01:06:38,000
u li l-lott sabiex jiddiġerixxu fl-ewwel jum ta 'klassi,

1219
01:06:38,000 --> 01:06:43,000
iżda għal issa huwa verament il-blokk bini ta 'kollox fehim

1220
01:06:43,000 --> 01:06:46,000
li kien għaddej fuq ġewwa ta 'memorja tal-kompjuter tagħna,

1221
01:06:46,000 --> 01:06:49,000
u eventwalment aħna ser tease dan apparti bi ftit għajnuna

1222
01:06:49,000 --> 01:06:51,000
minn wieħed mill-ħbieb tagħna fil Stanford.

1223
01:06:51,000 --> 01:06:56,000
>> Professur Nick Parlante fil Stanford għamel din is-sekwenza vidjo isbaħ

1224
01:06:56,000 --> 01:06:58,000
minn kull xorta ta 'lingwi differenti li ddaħħlu

1225
01:06:58,000 --> 01:07:00,000
dan Binky ftit karattru Claymation.

1226
01:07:00,000 --> 01:07:03,000
Il-vuċi int ser tisma fi ftit Sneak preview ftit 2

1227
01:07:03,000 --> 01:07:05,000
huwa dak ta 'professur Stanford, u int jkollna

1228
01:07:05,000 --> 01:07:07,000
biss 5 jew 6 sekondi ta 'dan id-dritt issa,

1229
01:07:07,000 --> 01:07:09,000
iżda dan huwa n-nota li aħna ser tikkonkludi llum

1230
01:07:09,000 --> 01:07:11,000
u jibdew nhar l-Erbgħa.

1231
01:07:11,000 --> 01:07:15,000
I jagħtuk Pjaċir Pointer mal Binky, il-preview.

1232
01:07:15,000 --> 01:07:18,000
[♪ ♪ Music] [Professur Parlante] Ħej, Binky.

1233
01:07:18,000 --> 01:07:21,000
Wake up. Wasal iż-żmien għall-gost pointer.

1234
01:07:21,000 --> 01:07:24,000
[Binky] X'hemm li? Tgħallem dwar pointers?

1235
01:07:24,000 --> 01:07:26,000
Oh, goody!

1236
01:07:26,000 --> 01:07:29,000
>> Aħna se tara int nhar l-Erbgħa.

1237
01:07:29,000 --> 01:07:32,000
[CS50.TV]