>> David: Tere, minu nimi on David Malan ja see on CS50. Ja see ei ole teie tüüpiline keskkooli informaatika eriala kursuse. See kursus on vähe midagi erilist. Ja see pole, sest ma olen õpetamise ta. sellepärast et see on üks, meile meeldib mõelda, need vähesed kursustel, et tegelikult pigistab oma aju nii palju ja oma ajakava nii palju, et semestri lõpul te tõeliselt tunnete targemaks. Nii, et oli nii, nagu ma tunda, kui ma ise võtsin selle käigus juba 1996. Olin valitsuse peamine ajal siin elavad Mather House. Ja, I.

[Cheering] Nagu on teised, viie teised seal. Niisiis, ma olin valitsuse peamine ajal. Ja ma olin valitsuse suur, sest ma alati meeldinud ajalugu. Mulle meeldis riigiõiguse keskkoolis. Ja nii ma maha seda teed freshmen aastal seda, mida ma kõige paremini seda, mida ma teadsin, mulle meeldis. Ja ma alati olnud veidi geek, ma alati babble arvutitega. Aga mina, ehk irooniliselt tagantjärele, ma alati vaadatud poisid, kes võtsid arvutiteadus minu keskkooli, mu sõbrad nagu tõeline geeks. Ja veel lõpuks ka tegi, Teise aasta üliõpilane aastal olen seda vähe muidugi kutsus CS50, mis tegelikult oli ehmatasid mind minema oma uustulnuk aastal. Ja ma olin kasutaja assistent ajal. Seega olin ma kindlasti juba kvalifitseeritud, vähemalt tuleb nende hulgast, need geeks kes ma tegin nalja keskkoolis. Kuid ma olin hirmunud. On see oli see maine ajal ja võib-olla veel osa, et see oli, oli see hirmutav muidugi. See oli palju tööd. See oli raske ja veel, see on üks nendest asjadest, kus, mu Jumal, puukoor oli palju hullem kui tema hammustus. Pidin Teise aasta üliõpilane aastas, esimest korda tegelikult leida kodutööd lõbus. Ja ma ei ütle seda lihtsalt pigi seda muidugi teile. See oli tõeline realiseerimine minu jaoks. Nüüd ma arvan, ühel hetkel, ma ei ületada eraldusjoont true geekdum kus ma tegelikult kasutatud ootan reede õhtul, sest ma võiks käppyrässä ees mu väike MacBook ja töö CS50 probleem seab. Niisiis, sel hetkel, ma arvan, oli selgelt üle eraldusjoone. Ja meie eesmärk selles muidugi ei ole omakorda kõik sind selle isiku, vaid lihtsalt öelda, et seal on vähe midagi erilist sellest muidugi vähe midagi erilist umbes infotehnoloogia üldiselt eriti nendel päevadel. Ja rohkem harjutada me oleme kõik sattusid tehnoloogiate rohkem mänguasju jätkame umbes taskus, mis on ise arvuteid. Ma mõtlen, mu iPhone on tegelikult kõrgem täitmisel arvuti kui minu sülearvuti oli kolledžis. Seda saab teha palju puhas asjad need asjad. Ja nüüd, enamik meist selles ruumis, ilmselt lihtsalt kasutada teiste inimeste tarkvara, teiste inimeste tööriistad, teiste inimeste probleemid lahendada, sest me läheme iTunes, me laadida mõned APP alates App Store ning Walla me saame teha midagi tõeliselt puhas. Aga lõpuks see semester, siis saab inimene teha, et probleem lahendada. Võite olla isik lahendada mõned probleem, hoone app, et tarkvara, et vahend, et kas üks just amuses mulle amuses sind. Näiteks kontrolli, ütleme, iTunes'i teeki oma korter selgelt app, et on juba olemas või leiad shuttle sõiduplaanide kergemini näiteks. Nii et tegelikult, üks esimesi asju, mida ma ei võtmise järgselt CS50 oli jälle, see oli ilmselt selles kohas reede ööd ja laupäeviti, oli see võimalus ajal, kus Harvardi toimis shuttle busse. Ja kuni tänase päevani, on neil siiski trükitud sõiduplaanid. Paraku oli tõesti mingil online leidmise läbi kui järgmine shuttle oli. Nüüd ma ei hoolinud, sest kuigi ma elanud Mather ma ei olnud nende seas, kes üldiselt võttis shuttle. Aga mul oli palju sõpru Pfoho näiteks. Ja üks neist küsis minult, ma arvan, et ühel hetkel.

[Cheering] Okei Pfoho parem kui Mather ilmselt. Niisiis, üks mu sõbrad liiki sai mulle mõelda, et äkki ma kirjutada väike programm millist abi oma sõpradega vaadata shuttle sõiduplaanid. Ja nõnda sündis saamatult nimega shuttle poiss, see tükk leksikon, mis on püsinud teatud arvu aastate vähemalt üks osa upperclassmen. Tol ajal oli see see väike käsurea programm sarnase sisuga Dos. See oli alanud UNIX keskkonnas. Niisiis, see ei olnud väga seksikas üldse. Sa lihtsalt kirjutada paar käske ja ta ütles sulle, kui süstikud olid. Noh, nendel päevadel see on natuke keerulisemad. Ja see on tegelikult esindatud täpselt tüüpi projektidele, et õpilased selle kursuse lõpuks tegemise tingimuste lõpp. Nii, see on versioon neli, umbes 15 aastat hiljem Shuttleboy. Tundub Google Maps on natuke aeglane seal. Aga neile, kes peavad minema siit pärast klassi ja lähevad, st alates Memorial Hall ja vaja minna kuni, ütleme, Quad. Noh, võite lahkuda kahe minuti kaupa, see tõesti ei tööta sa veel, või teil on nii palju muid võimalusi, nagu teile soovida. Ja varsti saame pigi see alates CS50, siis on see sama pädevust SMS. Võite teksti Shuttleboy telefoni teel. Sa helistada Shuttleboy. CS50 telefoninumber sel aastal hästi, hämmastavalt see oli kättesaadav, 617-BUG-CS50. Nii, et teeb debüüdi kiiresti. Nii ei sea see lihtsalt veel, sest ma olen saanud noomituse eest, just nüüd on nii kuramuse suunatakse meie süsteem pea õpetamise kaaskodanike poolt mobiili. Niisiis, sa lihtsalt saada temalt, kas teil on küsimusi shuttle ajakava nüüd. Aga varsti tuleb täita. Niisiis, muud asjad, tegelikult, et me ise veetis sel suvel on tõesti ettevalmistamiseks käesoleval poolaastal oli terve hulk muid probleeme, et tahame lahendada. Näiteks seal on terve hulk asju, mis läheb selles campus teatud päeval. Ja tegelikult, teisiti öeldes, seal on terve hulk asju juhtub praegusel campus, et ma kindlasti kunagi ära. Ja kuigi ma olen nüüd hämmingus, kuidas paljud asjad, mis on pooleli, ülikoolilinnak, ma ikka ilmselt kunagi leida aega. Aga Walla, isegi seal, CS50 luennolla. See, kuhu on, nii et see oli, oli see programm me wrote koondada kõik sündmused ülikoolilinnak. Ja see on midagi, mida teised õpilased sama loomulikult tegeleda omal käel. Ja oleme koostöös teiste üksuste ülikoolilinnakus tõesti see võimalik on. Aga käsk CS50 seda mõistet, et kõik need vähe programme oleme töötanud, kas see ühe või kas üks liidetakse kõigi Harvardi uudised ühes kohas, kõik Google News, kõik need asjad on, mida kutsutakse API, rakenduse programmeerimise liidesed. Ja see on lihtsalt fancy rääkida võime rendile teiste inimesi, siin saalis tegelikult teevad midagi, et samu andmeid. Niisiis, selliseid sõnu lõpuks, kui sa otsustada rakendada lõplik projekt, mis on seotud uudiste või sündmuste või kaardid, ning me vähemalt nii muidugi teeb, et kõik kergemini sel aastal pakkuda Teile liides; omamoodi funktsioon, nii et rääkida, tarkvara, mida saab kasutada oma projektide kõrgemate kus õpilased ehk läinud muiste sest see raamistik ei ole olemas nende jaoks. Ja jälle see kõik algas minu jaoks vähemalt umbes 15 aastat tagasi rakendamise Shuttleboy. Siis ma emailitaks sõber Ken on Pfoho. Ma ütlesin hei what do you think? Kas see kasulik? Ta saadetakse ta välja Pfoho avatud loetelu ja Walla, kõik need aastat hiljem olen ilmselt ikka lüpsi seda projekti. Ja kena asi, ja see on koht, kus liiga loomulikult meeldib see inseneri ja infotehnoloogia, ma arvan, on vähe erilist, on see, et kui sa oma kodu toimib ja kui sa oma projekte selle kursuse, siis tean, paljud neist, jah, oled kõrvale panema ja tegelikult ei kasutavad uuesti. Aga mõned see, siis. Ja seal on see tõesti võimas asi, vähemalt minu jaoks, see on tõesti põnev asi, kui teete midagi ja teised inimesed tegelikult ravi, teised inimesed ei ole lihtsalt naerata ja pat teie taga ja siis omamoodi minna oma elu. Nad kasutavad tegelikult, mida sa teha oma elu isegi kui see midagi nii rumal või nii lihtne kui lihtsalt leida, kui nad saavad siit välja jõuda järgmise ümar Quad. Niisiis, selliseid sõnu lõpuni, see on üks eesmärke, seda muidugi; anda kutid lihtsalt kindlaks mõned probleem, kas see on ülikoolilinnak või loodetavasti ka väljaspool ülikooli, ja tegelikult kasutada oma oskusi, oma meeles ja seda probleemi lahendada teatavates poolt tehnoloogiliselt. Nii, see on ka muidugi nagu me ütleme ainekava ja kursused ametlikku kirjeldust, mis õpetab sulle, kuidas mõelda ja see õpetab teile, kuidas probleeme lahendada tõhusamalt. Noh, mida see tähendab? Noh, kui sul on 600 megahertsi taskus või kolme gigahertsi alusel oma laua kodus, siis on võimalik lahendada palju probleeme tõhusalt lihtsalt lõikumiseks jõuvõtete. Aga seal on palju probleeme selles maailmas, olgu see otsib, siis öelge, Facebook võrgu või interneti kaudu Google, et see ei ole oluline, kui kiiresti teie eriti arvuti on, pole kuidas kurat sa lähed otsing miljardeid veebilehti kiiresti kui sa tegelikult lähenemine sellele probleemile arukalt. Sul ei ole lihtsalt otsida, näiteks tohutu loetelu veebilehti maa peal ülevalt otsi midagi, mis on seotud mis tahes otsingu tingimusi otsite loodetavasti Google ja arvatavasti Google ja Facebook ja kõik need suured üksused on palju tarku inimesi mõtlema kuidas on võimalik leida andmeid kiiremini, kuidas nad saavad töödelda teavet tõhusamalt ning kuidas nad saavad lihtsalt üldiselt tagasta tulemusi kiiremini, nii et saate teha veel rohkem huvitavaid asju nende seadmetega. Ja jah, millised me mõtleme, aga mida, kuidas õpetada inimestele, kuidas mõelda hoolikamalt, rohkem algoritmiliselt. Noh, see väike visuaalne alati tundub, et minna üle samuti. Ja see tundub olevat meeldejääv. Ja olin isegi küsis just eile endine õpilane, oh sa lähed tegema telefoniraamat asi uuesti. Ja olen päris palju kohapeal otsustas igav kindlasti me ehitada telefoniraamat asi. Ja ta palus mind, kui sa rebis ta pooleks õigus, ma olin nagu ka jaa tehniliselt me rebis ta pooleks, kuid mitte viisil, arvutiteadus, kuidas ma saaks pisar see asi pooleks. Ja jah, siin oli probleem, et me esitatud juba mõnda aega. Nii, siin on telefoniraamat. It's sai vähemalt tuhat või nii lehekülgedel. Ja lihtne eesmärk käepärast väga reaalne maailm on üles leida, st inimene siin. Niisiis, Mike Smith, perekonnanimi algab S. Niisiis, ma olen tüüpiline inimlik, ma elavneb see telefoniraamatust. Ja keegi seal, mida sa, tüüpiline inimene, ei hakata leidmisel Mike Smith, ilmselt ei tea eelnevalt, milline lehekülg on ta tegelikult on. Parem, et sa minema umbes keskele, paremale. Ja siinkohal lugu, ma olen ilmselt N-või M, sa tead, et ligi pool teed läbi telefoniraamat. Selgub, viimane kord tegin seda eeskuju ma kuidagi leidsin end eskort osa. Nii, see on tegelikult mitte võrdselt kaudu M ja N kaudu Z. Aga täna oleme me tegelikult, et M, igav jah, nüüd olen kell M's. Aga mis on minu Buffee nüüd nagu normaalse inimese off tänaval? Kuhu ma minema järgmise jaoks Mike Smith.

[Kuuldamatu] Ja jah, just ilmselt selle poole, paremale, sest S tuleb pärast M. Ja nii siin on visuaalse draama. See ei ole tõesti pisaravool see pooleks, eks. I tüüpi petnud kehtestatakse keskuses. Aga me teame nüüd, et Mike on vähemalt mitte selle poole. Me saame sõna otseses mõttes viskame poolel probleem ära. Ja ma olen jäänud probleem, mis on põhimõtteliselt ikka sama asi, leida Mike Smith tõeliselt suur raamat. Aga probleem on nüüd pool suur. Kui ta oleks tuhat lehekülge enne, nüüd sain 500. Tead mis, ma saan sama asja uuesti. Võin liiki rekursiivselt korduvalt või teha sama asja. Nüüd ma ei ole päris nii S. Mul on T. Ja nii oh ma läksin natuke liiga kaugele. Aga ma tean nüüd, et Mike ei ole õigust, seal saab olema mõni klass Ükspäev kui ma lihtsalt ei suuda pisar dam asi, ma võin kihla vedada. Nüüd ma tean, et ta ei ole paremal. Nii, nüüd probleem on poolaastaga. Niisiis, ma olen läinud tuhande 500-250 lehekülge. Ja jälle, kui te jätkate loogika, jätkub matemaatika, ma olen tükeldamine see probleem pooleks, pooleks, poole kuni lõpuks ma kas kavatsete ei leia Smithi üldse ebatõenäoline, või ma lähen leida üks Otsin. Aga see, siis tekib küsimus, kas see on parem kui lihtne lähenemine ütle, sa tead,, Nope, B, ei, alustades vasakult paremale läheb lineaarselt läbi raamatu? Noh, instinktiivselt jah. See saab olema palju kiiremini. Aga kui palju vähem? Noh, kui mul on tuhat lehekülge telefoniraamatust või oletame 1024 neile, kellele meeldib volitused kaks, kui palju aega võiks mul jagada seda probleemi poole enne leidmine hr Smith?

>> Kümme.

>> David: Nii, kümme, paremale. Kui teil on 1024 lehekülge ja jagate neid pooleks, pooleks, pooleks, pooleks, mina, et kümme korda, mis tähendab, ma lähen alates 1000 lehekülge isikule Otsin kõigest kümme lehekülge kurvid. Ja see on selline kena, kuid te teate, kui mõtled seda olete seda teinud juba kõik oma elus. See ei ole nii dramaatiline. Aga nüüd, et telefoniraamatus ei ole ainult Boston, see on kogu USA või kogu maailmas ja see asi on miljardeid lehekülgi, seega kujutan ette telefoniraamatu nelja miljoni lehekülje. Mitu lehekülge lülitab ma lähen on teha maksimaalselt leida Mike Smith neli miljardit leht telefoniraamatu?

>> Logi baasi kaks.

>> David: Nii et jah, kui sa oled selline matemaatika tüüp see on logaritm alusel kaks. Aga kui sa arvad, 4-2000000000 to one miljardi nii pool miljardit. Ma mõtlen, et tegelikult läheb whittles ise ette üsna darn kiire. Tegelikult 32 halvings kohta telefoniraamat isegi neli miljardeid, ma saan näha ühe lehekülje. Ja siis see kraam muutub võimsaks, arvan ma. See on siis, kui neid ideid saada kaalukad kui teil on neli miljardit leht probleem ja 32 samme leiad isiku otsite. Ja nii see on, mida me mõtleme, kui ütleme, et saate teada, kuidas mõelda hoolikamalt, rohkem algoritmiliselt, arukamalt umbes probleemide lahendamisel. Ja kasu on tohutu, kui tegelikult võite seda teha, ja jälle, et selles punktis Googles maailma Facebooks kes on luksus, millel tohutu andmekogusid. Sa pead lähenemine nendele probleemidele sel moel muidu see lihtsalt ei hakka tööle. Noh, mis on mis ei õpilane tegelikult meenutavad? I, meile meeldib teha asju, mis on natuke rumal mõnikord omamoodi nüristama, mis on muidu palju uut materjali. Ja nii ta tegelikult on see endine õpilane saatis mulle selle lingi, mida ma läksin edasi, lihtsalt peksab ja siis kahetses ta lõpus tõmmatakse üles uTube siin. Niisiis, ma arvasin, tahaksin jagada mitte-arvuti teadlane tähendab, kui ta pisaraid telefoniraamat pooleks.

[Naer]

[Silence]

[Kuuldamatu]

>> Sa tead rohkem kui 200 lehekülge, kena puhas liin, õiguspärase pisara.

[Naer]

>> David: jah, ma arvan, tema viis asju. Niisiis, mida ma sain läbi selle käigus kõik need aastad tagasi on jah, Shuttleboy ja siis jah kraad arvuti teadust ja siis jah PHD infotehnoloogia. Ja see pole see, mida me üritame omakorda kõige õpilased selle kursuse võtta. Enamik teid selles muidugi ei kavatse minna suurte infotehnoloogia. Mõned võite alaealine, kuid mõned teist see terminal muidugi. Ja see on täiesti trahvi, sest muidugi on tegelikult üles ehitatud viisil, kus isegi siis, kui sa lihtsalt maksavad oma maksud mitu kuud ja sa tõesti keskenduda ja sa tõesti võtta nii palju tähelepanu selle käigus, kui saad, siis võtab ta Tegelikult on hästi varustatud, et minge tagasi oma maailma majanduse, bioloogia, psühholoogia, kohaldatakse matemaatika ja tegelikult kasutada, mis on lõppkokkuvõttes sama huvitav muidugi, nagu me loodame, et kontseptuaalselt, sest see on täiesti praktiline. Ka see on midagi, mis võib-olla natuke haruldane leida. Ma arvasin ma jagada mõned märkused, et õpilased eelmisel sügisel panna see viimaste aastate kii guide kui küsiti, mida sa tahaksid öelda tulevikus õpilastele. Noh, kui te pole juba vaadeldi neid märkusi, üks õpilane ütles selle käigus võtta õiglase summa teie aeg läbi. kuid kui paned oma töö täiesti uus maailm, tervikuna, kui paned tööle, kui paned töö, igav, nii et see on tema grammatika mitte minu, nii et kui paned, pane töös, täiesti uus maailm avab teile. Hämmastav, kui palju ma õppinud ainult 12 nädalast. Teine üliõpilane kirjutas, siis parem seda või sa lähed kahetsen seda. Teine kirjutas, veidi rohkem keerutamata, siis kick oma perset ja jätan teid tunne suur. Ja siis lõpuks see üks on võib-olla ma ei näita ainult kirjalikult, kuid teine alt siit.

[Naer] Niisiis, ma ei ole kindel, kui sul on palju sõpru, kes võttis seda muidugi, kuid me sellist tegi palju kahju eelmise aasta õpilastele. Me tutvustas alguses mitu loengud, mõned viktoriinid, paar probleemide komplekti, see mõiste lolcats. Sa ei saa aru, mida ma näen siin vaid hetk sa näed noor mees nimega õnnelik kass, kes on juht nn lolcat. See on üks loll internet ettepoole, et ma arvan ausalt vastuolu nende kahe härrad siin ja mida me nüüd ekraanil on võib-olla.

[Naer] Üks sobimatu kasutab selle teatri kuupäevale.

Ja miks ei tee me veidi rohkem tõelist natuke rohkem isiklikke see mõiste tegelikult lahendada probleemi tõhusamalt. Lihtne probleem päeval üks iga kool on istuda või püsti ning alustada loendussüsteemid üliõpilaste õigust nimeline kehvasti. Noh, kõige naiivne, kuid siiski väga õige lähenemine, et õpetaja võiks olla üks, kaks, kolm, neli, viis, kuus, seitse, ja me tahaks olla siin juba mõnda aega. Niisiis, milline on marginaalne paranemine selles isegi, et te oleks võinud teha nii laps? Kuidas te arv inimesi kiiremini? Ja ärge hakake lugemine mu enda juhiseid? Mida olete teinud, nagu laps? Alusta lugedes tulid kahekesi, paremale, nii nagu ma olen päris hea kahe, nelja, kuue, kaheksa, kümme, 12. Nii, et midagi huvitavat paremale. Niisiis, kui palju paranemine on see, et seal on? Nii, see on ilmselt kaks korda. See võtab mind pooltki nii palju aega. Aga sa tead, mida, nagu me leiame kogu selle semestri suur asi, nagu kiirendades oma sõiduaega poolt lihtsalt kahega ei ole nii huvitav, sest analoog siin arvuti maailma, et ma olen CPU Ma olen arvuti ka kuradit, kui ma lihtsalt oodata 12 kuud, 18 kuud, mul arvuti lihtsalt suutma oma olemuselt arvu järgi gigahertsi pean ma olema võimalik arvestada inimesed selles ruumis kiiremini. Niisiis, selliseid, selliseid lineaarseid speedups nagu teguri kaks kolmega, isegi kümnekordselt, kes hoolib? Õige, me ei viska riistvara probleem. Saame ootama asju teha. Me saame arendada kiiremini masinaid. Aga intellektuaalselt, jah, et oli selline tark, kuid see ei ole tegelikult põhjalikult muuta probleem. Ma olen ikka läheb alates vasakult paremale, eest taha. See on tõesti sama algoritmi. Aga Pakun, et me saame teha paremini. Me saame seda teha targemaks kui seda ja seda täiesti kiiremast rakendamisest. Aga seda näidata, peame teile huumorit meile üks hetk. Ja see on sel hetkel, kui ta saad mulle rääkima vähem ja sa räägid veel. Aga ma vajan sind ellu järgu koos, mis on, kui te mulle huumor, palun püsti tõusta. Suundades siin laual, tead, eks, paar olete istuda. Need teid tagasi, seal läheme, igav. Aitäh. Nii, programm on siin enne sind. Oled nüüd arvutite täidesaatva seda programmi. See on üsna mõistetav selles punktis. Jah, siis peaks olema number üks. Saa? Õigus, paljud olete ilmselt mõtlemine see juba niikuinii esimene uustulnuk aastal. Niisiis, arvan ise, sa oled number üks. Nii, kolmas samm siin Parittua kellegagi seistes, lisage kaks arvu kokku ja võtab selle summa kui oma uue numbri ja me teeme terve mõistuse kontrolli.

[Müra pärineb rahvahulga] Kas sa tead, kui palju me oleme?

>> [Kuuldamatu]

>> Nr [kuuldamatu].

>> Meil on vaja saada vastus nuppu.

[Silence]

>> Jah.

[Müra pärineb rahvahulga]

>> David: Sel hetkel algoritmi tuleks likvideerimismenetluse alla.

[Müra pärineb rahvahulga] Võibolla oleks pidanud minema minu lähenemine ju.

>> 43.

>> 163 kohaselt.

>> David: Ooh aritmeetiline ees 300 pluss inimesed.

[Naer] Mis meie lõplik ühtivad saab olema?

>> 180.

[Naer]

>> 1200.

>> 386.

>> David: 386, ja kas te olete viimane alaline? Kas see kõik? Kas tead vastust?

>> Mis?

>> David: Tead, mis on vastus? Me ei toonud vastust võtme meid nii, 386 on tegelikult täpselt õige vastus esmakordselt.

[Cheering]

[Aplaus] See on okei.

[Aplaus] Väga, väga ilusti tehtud. Niisiis, milline oli Buffee sest see kindlasti tunda veidi aeglasem kui minu väga lihtne, kuid siiski väga õige lähenemine lihtsalt läheb onesies ja twosies ja lihtsalt saada ta teha vasakult paremale. Aga mida tegime tõesti ainult seal teha? Noh, kui oli umbes, oletame, 400 teie seisab ühe punkti ja siis pool teid väga kiiresti, mida ma võiks öelda, tahtis istuda. Nii, poole sa istusid, läksime 400-200 siis 100 siis 50 siis 25-le. Nii et jällegi, seal on sama lõhe ja vallutada idee oli meil telefoniraamat. Jällegi, iga iteratsiooni me poole probleemi ulatust, me poole, me poole ta. Nii et teoreetiliselt oma algoritm peaks ööbinud palju kiiremini kui minu lineaarsest lähenemisest, sest minu lähenemisviis olen võtnud ehk 400 astmete või võibolla kui ma pisut kavala 200 sammu. Aga sinu oma oleks olen võtnud palju vähem, eks 400-200, 100, 50, 25, 13, kuus, seega on vähem kui kümme sammu end võrreldes minu 200 või 400. Ja seal on seed tõesti huvitav idee. Ning jah, matemaatiliselt, mida sa just tegid oli midagi, mis on vähe logaritmiline looduses poolt samamoodi baasi kaks, me jagatud kahte ja kaks veel. Ja me uuesti käesolevast hiljem käesoleval poolaastal. Aga seal on jälle väga intelligentne rakendamist. Ja me lihtsalt kriimustada pinda väga tark väga tark tõhusa lähenemisviisi probleemidele, mis me võiksime lõpuks lahendada. Nii, kes on need inimesed, sa lihtsalt vestlesid kui lühidalt? Ühine mure muidugi, nagu see on, et igaüks vasakul sina ja igaühe õigust peate selgelt teada rohkem kui sina. Noh, see absoluutselt ei ole. Ja tegelikult viimastel aastatel, seda muidugi teinud ühiseid jõupingutusi, et jõuda nende vähem mugav, nii rääkida. Ja, et me mõistame ole inimesi, kes pole kunagi puudutanud arvutisse enne, sest see on tõesti raske leida siin lähedal nendel päevadel, kuid inimesed, kes kasutavad e-posti, kasutada Facebook, võibolla isegi just nüüd, aga ei pruugi olla päris kindel, mida teha, kui midagi läheb valesti või kui neil palutakse midagi tehnoloogia, tead, käed tõusevad või nad sellise lükke riistvara sõber, kes on ehk rohkem kursis selle kui nemad. Noh, need on mõned statistika eelmise aasta poolaasta kohta. Niisiis, kui küsitakse, siis palusime meie 400 nii õpilased eelmisel aastal, siis tead, milline on Teie tasemel mugavust puutuks Selles klassis ning 34% kirjutas ise alla kui nende seas, vähem mugav. Niisiis, kui olete jõudnud sinna tuppa ja veel mõtlesin nüüd, et sa tead, mida see mõiste vähem mugav kirjeldab mind, tean, et sa oled väga hea firma. Aga aru ka, et kui oled tulemas see muidugi tausta infotehnoloogia ja sa olid tõesti, et geek keskastme koolis ja keskkoolis, kes oli kirjutada koodi ja õpetuse iseendid keeles hästi, et trahvi liiga, sest seal on kindlasti nontrivial suurusega publik selle taustal samuti umbes 13%, viimase aja jooksul. Ja siis, seal on kõik teised, justkui keegi, kes ei usu, et nad vähem mugav, nad kindlasti ei usu nad mugavam kuid nad just muidugi midagi sellest välja. Niisiis, mõistma seda muidugi ei tõmmata üsna spekter õpilastele. Ja panna see konkreetsem, 71% õpilastest, möödunud aastal oli null kursused taga. Niisiis, kui sa oled sisestamise seda muidugi mõtlesin oh igaüks, kes võtab CS50 oli arvutiteadus viuhti keskkoolis, see pole nii. Enamik inimesi on arvatavasti lihtsalt huvitatud. Ja mõned, jah, absoluutselt võtnud mõned kursused, osa või vähemalt üks inimene eelmisel aastal oli võtnud viis kursusi varem. Niisiis, me kindlasti on mõned võõrväärtuste kuid taas liha kõver on neis madalamad väärtused kokku. Ja veel üks huvitav statistiline jagasime viimase paari aasta jooksul on soolise suhe. Nii ajalooliselt, vähemalt arvutiteaduse on natuke mees naine viltune. Ma paar aastat tagasi oli see palju suuremad kui eelmisel aastal. Nii et me oleme peaaegu nüüd% 40 tasemele. Ja kui ma ei viska alla kadalipp just huvides võttes kolmanda sektordiagramm järgmisel aastal, see on isegi õiglasem. Tuletan meelde, et seal mingit põhjust alates kursused perspektiiv, et meestel ja naistel ei tohiks registreerimisega sedalaadi muidugi. Suhteliselt võrdne arv ja realiseerida kuni 38 protsenti, 48 protsenti, me oleme tegelikult üsna hea meel, et me oleme peaaegu et vähemalt statistiliselt isegi väärtus 50%. Niisiis, kui teil on tegelikult naissoost, tehke ülejäänud Kinnitan ka, et see ei ole tegelikult meeste pärusmaa klassis. Noh, see lihtsalt nii juhtub olema CS50's 20. sünnipäeva. Ma hästi aitäh.

[Cheering]

[Aplaus] See on väga kena, sest me tõime koogi jaoks te tegelikult. Ja nii, kui väljute siin täna hiljem, saate tegelikult saada võimalus kohtuda paljude kursuste õpetamise stipendiaatide kes tulen ikka koridoris. Ning jah it'll olema kena omamoodi motiveeritakse viis kohtumise õpetamise stipendiaatide. Aga me ei võta reisi kuni väike pagariäri ja uuesti kooskõlas kursus on mänguline iseloom samas siiski ootab nontrivial palju tööd, samas meil oli lõbus. Aga meil on üks nendest koogid teile.

[Naer] Niisiis, kui sa naerad see on tegelikult hea, sest isegi kui sa oled seas üks neist vähem mugav vähemalt olete sellest teadlik. Need teid 14 protsenti võiksite selle maitse.

[Naer] Ja siis, kui te ei tea, mida põrgut toimub just nüüd, meil on ka see ülejäänud teile.

[Cheering]

[Aplaus] Niisiis, neid hoitakse peenestatud tükkideks väljaspool kui me räägime. Nii et taas, let's võtma asju soont ja vähemalt mõningaid põhilisi üürnik, et me siis enesestmõistetavaks ülejäänud käesoleva semestri. Niisiis, me kõik ilmselt teame, et arvutite lõppkokkuvõttes taanduvad kuidagi nulli ja need, neid asju nimetatakse bitti. Mida see tähendab? Aga te ei mõtle seda ausalt nagu lambipirn, natuke on lambipirn, mis on kas või see välja lülitada. See on lüliti, see on kas või see välja lülitada. Nüüd arvuti teadlased üldiselt arvad ära, kui mitu nulli meelevaldselt ja, ja mõiste kohta üks. Niisiis, kui sa viska valguse lüliti, mis on üks selle väljalülitamiseks see null. Või võrreldavalt omakorda valgust, mis on väärtus tõsi see välja lülitada, et tema väärtus on vale. Niisiis, need on vaid sünonüümid. Aasta lõpus päev, jah, kõik arvutuse kõik asjad, mis läheb alt Hood arvuti ei lõppkokkuvõttes taanduvad nulli ja ones. Ja kui te lõpetate mõtlema, see on päris tammi tähelepanuväärne, mida maailmas on tehtud neid põhiplokke sealhulgas mõningaid seadiseid oled ettevõttes sinu käsi. Noh, miks on nullid ja need on kasulikud? Mu jumal, isegi reaalses maailmas meil on vähemalt kümme numbrit null läbi üheksa. Miks nii vähe? Noh riistvara osas on väga lihtne. See on palju lihtsam esindada kaks riiki, õigus. Kui arvutid on ühendatud müür, tavaliselt, siis on see lihtne allikas kahekomponentsete laadi. See on kas sisse või välja. Elekter on voolav või see ei ole. Nii, et on selline üks esialgne põhjustel, et maailm läks lihtsalt nullid ja need arvutid. Kuid te võite kasutada neid aluseid. Nii on see tegelikult natuke väike ekraanile siin, aga saame loota binaarsed või saame esindada midagi tahame kahekomponentsete nagu me, ütleme, koma, nagu me isegi tegelikult koos tähed. Ja jah, siin on kiire süsteem. Vaid paar minutit aega teil nüüd teada, kuidas arvutada, kuidas kirjutada, kuidas rääkida kahekomponentsete meelega oma sülearvuti. Noh, teil on maailmas kahekomponentsete, omamoodi nagu algkool veergude või väärtusi. Niisiis, algkool õpime seda need veerus on see kümneid veerus sadu veerg jne. Teisisõnu, miks on number teame 123. number 123? Noh, minu õpetaja õpetas mind see on neist veerg, see oli kümneid, see oli sadu. Noh, mida tegid see tähendab? Noh, et aru saada, mis kogumaksumus on, mis on muidu string numbrit, lihtsalt räsi kaubamärkide laual. Noh, meil on üks 100, nii see on 1 korda 100 ja siis pluss, mida kaks korda 10 on nii, et on 2 korda 10 pluss kolm neist, nii see on 3 korda 1, okei, ma tundub, et on saanud tagasi sinna, kus alustasin. Aga see väga lihtne protsess lihtsalt korrutades numbrit väärtusega veeru täpselt kahendsüsteemis on kõik umbes. Aga kahekomponentsete te kasutate volitused kaks ei volitused kümme. Nii, siin on rida kaheksa lambipirnid. Arvuti teadlased meeldib kasutada väärtused nagu kahe ja kaheksa ja 16 ning 24 ja 32, kuna nad kõik üldjuhul mugav väärtusi kasutada. Niisiis, kui me räägime kaheksa väärtuste jada on see nagu nimetatakse baidi. Ja neid päevi me harva räägime kõigest baite me räägime megabaiti gigabaiti ja teratavukaupalla nendel päevadel. Aga see on kõik lõppkokkuvõttes sama asi. Siin on kaheksa bitti AKA üks bait, just lihtsad erikeel. Niisiis, kõik need lambid on välja lülitatud. Niisiis, matemaatika on tegelikult väga lihtne. Nii et paremal, kuigi see on väike, et näha, on oma veerg, tulid kahekesi püksid, kaheksad, 16s, 32s, 64s, 128s. Alright, võibolla see on raske meelde jätta esimesel kuid see on lihtsalt kahega korrutada paremalt vasakule. Niisiis, sa võid alati uuesti seda. Noh, nad kõik maha, nii et tema 0 korda kohatäide 0 korda kohatäide. Nii, see on number 0 esindatud kahendarv. Teisisõnu, kuidas sa kirjutada number teame kui 0 binaarfailina? Noh, üks, kaks, kolm, neli, viis, kuus, seitse, kaheksa, ja tehniliselt just nagu kümnendsüsteemis, kõik need nullid, ei midagi lisada valem nad lihtsalt seal, sest me omavoliliselt otsustanud me tahan kaheksa need asjad järjest paremale. Kui nad füüsilisi objekte, meil on kaheksa, et nad pead kõik maha. Niisiis, me võiksime oled saanud kaotada üks null. Noh, kuidas sa esindama number üks? Noh, instinktiivselt sa lähed viska üks lülitid. Sa lähed sisse sibula kohta. Niisiis on number üks, sest me nüüd panna üks, lambipirn see edasi, üks seisukoht. Kuidas me esindama kaks? Noh, me oleme tegelikult toimub visata kaks lülitid nüüd vähemalt võrreldes selle riigi, peame me muutma kahe's veerus lülitada need kolonn ja nüüd on meil väärtus üks Kaksittain veerus. Nii, et tema koguväärtus kaks. Nüüd, kiire vaimne liikumisvajadust; Mis juhtub järgmise jada? Kuidas praegune number kolm? Noh, mul on vaja üks Kaksittain veerus, üks kolmekesi kolonni ja ah ha. Nii, nüüd olen suurendatakse, et üks. Ja nüüd see sama põhimudeli kordub. Mis number neli? Noh vaatame, ma lihtsalt vaja üks püksid veerg ja seejärel nullid Kaksittain ja ones. Nõnda siis jätkub nii. Ja see on lihtsalt see sammud. Ja mõiste kahekomponentsete ei ole tegelikult kõik, mis keeruline. Ülal on meil kaheksa nulli. Allpool et meil on seitse nulli ja ühe. Allpool et meil on kuus nulli, üks ja null ja see on binaarne. Now, thankfully, we computer scientists, we programmers by terms end are not going to often be writing in binary, talking in binary, thinking in binary because we've built many layers of the traction on top of that. In fact, people rarely talk about bits except in a networking context they talk about bytes because one bit, not that useful, eight bits these days still not that useful, but at least eight bits, one byte is at least getting us toward more useful units of measure. But, when we start looking underneath the hood, when we do certain problems such as look at files and look perhaps at network traffic, it will become interesting to know how you're representing data because you're going to have to figure out how to display that same information. And, in fact, we, if we only have zeros and ones, how do we go about representing, say alphabetical letters? Well, we're going to have to have some mapping between binary and letters. But that's as of yet unclear. But to hammer this point home and to give me a break from speaking at, I thought I'd pause for a moment and see if we can't recruit eight volunteers, one byte eight people. Can I get eight people for whom it is not too awkward to come on up. good, good one, two, three, four, five, six, seven, eight very enthusiastic eight, come on down. So, you all, for just a moment here, oh and you have to be willing to not be on the internet because there is in fact a camera in the back of this room. So, turn back now if you don't want to be on the, hello mom, in perpetuity. So, let's see, you here will be the 128th column. And let me ask that you simply hold this before you. And actually, if you could scooch this way just a little bit, then I will get out of your way. You'll be the 64's column, you shall be the 32's column and the 16's. 32's, 16s, 8's, 4's, 2's and 1's. All right. So perfectly lined up with the place holders from before, but we need a little bit of mapping, so a quick set up. We just need an arbitrary way of mapping binary numbers, which really could be converted very easily to decimal numbers. So we need a way of converting numbers to letters if our computers are actually going to show us emails or type URL's or actually display non numeric information. And, in fact, there is a system for that, it's called ASCII, an acronym whose meaning is not so interesting, but whose utility is. This is just a mapping from letters to numbers and there's actually a lot more numbers on the screen, and you guys, don't worry, aren't going to have to test yourselves with this in just a moment. But there's a mapping between numbers and letters and I'm just going to get us started by pointing out a couple of these. The numbers of interest right now are going to be, whoops, are going to be this. Whoops. So in this column here, I can't seem to zoom in simultaneously, we have decimal. Dec for decimal. And then we have the character on the right hand side. So if I hop over into this column, thought it's a bit small on the screen, the number 65 represents what letter? Capital A. And the number 97? Lowercase A. All right. So those two alone, right, so do not go home and try to remember ASCII chart. Come quiz time, do not try memorizing an ASCII chart. Memorize two, 65 is capital A and 97 is lowercase A. And from there you can bootstrap yourself to all of the other alphabetical characters. But all this chart says, and I just downloaded this chart from ASCIItable.com, this is a standard that's been around for many, many, many years, but most computers still use it. What we now have is a means of encoding alphabetical information using what's ultimately numeric. So if these guys are just switches, light bulbs, computers, we can actually convey messages. So each of you has some hints on the back. We're going to have three rounds here where these guys are going to spell out in English, in ASCII, a very short message, a three letter word. It will involve them either raising their hand, thereby representing a one or just standing there awkwardly, thereby representing a zero. So why don't we proceed immediately with round one and you can either raise or not raise your hands. So the audience doesn't get off the hook. What number are they currently representing? 66. Right. Not hard because we have a one, a hand up in the 64s column, a hand up in the 2's column. 64 times one plus two times one is 66. They're representing the number 6, which means the first letter is B. So not too bad, right? Round two. First letter was a B.

[Naer]

>> Seventy Nine. 

>> David: Can someone second that? Yes. All right. So 79, which means it's now an O. So B,O. There's a third letter. Actually that is kind of, yeah. Third round. Third and final round. What number is this? I heard an 87. Someone else agree? All right, yeah. This is in fact 87, which maps to, and this is a very clever set up at which point you all B, O, W, it's bow. Very good. So actually besides that little souvenir, that was not a very enthusiastic applause, so I'll take care of you. So we do have a little something for these guys here now that they just appeared on center stage doing perhaps the geekiest thing they could. So maybe if we could humor them if only because I'm feeling a little bit awkward now. A little round of applause for these guys here. 

[ Applause ] All yours. All right. Thank you very much. So, so, it turns out that we can take this one step further, but you are now entering a community of people who understand things like this. 

[ Silence ] It's slowly spreading, yes? 

[ Laughter ] It's not cool that you understand this now. So we've already done some damage here today, but yes, there is now such a thing as geek humor that you might just catch a little bit more on to. So what are we going to do throughout this semester? So there's 12 weeks, zero index, so 13 weeks in total. You'll find throughout the semester that computer scientists tend to count starting from zero for reasons that will soon become clear. But what we're going to do this week, starting this Friday, is introduce you to programming. Now you may already be coming at this course with a background in the same, and that's perfectly fine, but we'll also be able to introduce some more sophisticated topics than are typically covered, things like events and threading, so just to toss out a couple of buzz words for those unfamiliar. But what we're going to do is not dive into what the typically traditional language like Java or C++ or C sharp catch phrases that you might have heard in the past, but we're going to use a programming environment, a graphical programming environment that was actually developed by MIT's media lab. And this is an environment that allows you to program, quite literally, by dragging and dropping puzzle pieces that fit together logically that lets you implement these things called loops and conditions and Boolean expressions and you can actually, on day one, after this Friday, write a program that actually some of your friends might care about. So in yester year, say when you've taken a computer science course in high school, odds are one of your first programs was the equivalent of hello world, like wow mom, I just made the computer type some characters on the screen. It's a very underwhelming experience. Much more interesting is it to implement a little something like this, as one of last year's students did. So I give you the work of a former classmate. It's a love story, of sorts, about dancing cookies. 

[ Music ] So this was actually from a student who had never programmed before. And just to give you a teaser of this interface, and we're only going to use this for one week time, really to get the comfort levels up and to really get folks excited about what you can actually make these machines do, this is an environment where you'll be programming by, for at least a week, just dragging and dropping puzzle pieces that fit together, as we'll see, in a logical fashion. And it lets you do fun, silly things quickly. And for any of you who are a little bit familiar with things like Java and C++, it's usually a good semester or two or three before you finally get to start writing something that another person might actually enjoy watching. Well, in week one of the course, or the second week, zero index, where we dive into a little more traditional environment. In this course we'll spend much of our time on a language called C. This is one of the earliest languages that, unlike Java, actually gives us much greater access for better or for worse, to manipulating hardware and actual memory, and we can do a lot of damage with that. In fact, any time you read of web servers being exploited or computers being hacked into, very often to this day it's the result of people having run software in a language called C or C++ without sufficient care given to what are called buffer overruns or lengths of arrays, so some fairly technical concepts that are not that hard to understand, but there's been a lot of humans making a lot of mistakes for years and with this language we'll actually understand some of those security implications. But each week, typically, we'll introduce also an interesting domain that will inspire that week's problem set. So we'll also take a look this week at the field of cryptology, cryptanalysis, the notion that you can encipher information in such a way that people can't read your messages, but if clever enough perhaps you can, in fact, crack what are otherwise secret messages. In week three we'll then look at some basic fundamentals of computer science like searching and sorting and we'll actually look at this notion of recursion, how to debug things. In short, we'll take things up to the level of problem solving and not so much about mere syntax and implementing short little cookie cutter programs. In week four we'll introduce more sophisticated problems still. What does it mean to manage memory? What does it mean to run out of memory? What does it mean to actually segfault, if you've heard this expression, and odds are you haven't, but very bad things happen and frankly by terms end you'll understand terms like my code segfaulted which actually is generally not going to be a good thing. But then again, we'll introduce some domain specific stuff. So actually one of my internships during graduate school was to work for the local Middlesex County District Attorney's office doing forensic investigations in a digital sense. The local Mass state police would bring to our office hard drives and floppy disks and sometimes for no reason mice and keyboards. And we would be tasked with finding evidence. Now it turns out, maybe just an FYI, that the criminals in Cambridge, Massachusetts, at least, not necessarily that clever. Very often our forensic analysis boiled down to booting the computer up and double clicking on the My Documents folder, and therein laid the evidence. But what we'll do this week is give you a sense of what it actually means to store information on a hard drive, on a flash drive, and why can't otherwise private information be disclosed to third parties when you drop off a computer to be repaired or even when you discard it. Well someone might very well be sifting through those hard drives and it's really not that hard to find data if you know how to look for it. Well, in week five we'll look at more sophisticated data structures, tools and techniques that you can use ala phone books and ala searching huge data sets much more intelligently. And the week's problem set will task you competitively to see just how fast the code you can write is and how little memory you can use. Toward terms end though we'll take things up to a higher level in terms of programming languages and put C behind us and introduce a web programming language known as PHP, one of the popular languages these days. Much of Facebook is still written in PHP, at least outward facing, and it's just a very easy language to learn quickly once you already know another. So with PHP we'll be able to solve problems and implement websites that do interesting things. The news site I showed you, the events site, the shuttle boy site, all of those all happen to be written in PHP. But by no means is that prerequisite. What you'll also find throughout this course is that you're not going to exit this course knowing C. You're not going to exit this course knowing PHP. Those are not interesting skills to claim, but knowing how to program, knowing how to use data structures and algorithms in an interesting way, that's a compelling story. Even I, all these years later, throughout college and graduate school, the only time I ever learned a language was probably in CS50 where it was still taught in C and CS51, which is one of the successor courses. Everywhere along the way since has been go learn this language and then work on this problem set because computer science is not supposed to be about here's a language, let's spend seven weeks teaching you where the semi colons are. There are much more interesting ideas out there. Databases, for one. And in week two we'll introduce you to this query language called SQL that'll allow you to store information in databases and actually implement some fairly interesting final projects. The week after we'll look at what's called client side programming, doing interesting things on a user's computer, taking advantage of their CPU cycles, doing things ala Google maps and these websites that actually use JavaScript, which is actually a language we'll introduce to let you do client side things, make more interesting, more sophisticated user interfaces, but at the end of the day have to be really mindful when implemented of a lot of sticky issues like network speeds, network performance and security. So it's not about again just coding something up that's fun to use or pretty to look at, but actually thinking about the design that'll be the interesting process. And then, the end result aesthetically will often be a really neat toy to show yourself or a friend. And then we'll look at hardware. We're going to take for granted that there are these physical boxes throughout much of the semester that will do what we tell them to do. But how are they doing that. So we'll actually take a peak under the hood and talk about what a compiler really is, what a CPU really is and actually consider what's making all of this fanciness from stupid YouTube videos on down possible. So what are the expectations? Attending lectures and sessions, completing nine problem sets assigned roughly weekly, two quizzes, the final project and there is in fact no final exam. Grades, it's always a question, broken down as follows here. You can take the course pass-fail. But let me say it here, and I've said it many times. I personally care relatively little about grades. I think they are a wonderful, well, they are a useful pedagogical tool with which to motivate and unfortunately sometimes de-motivate, but you'll find in this course that at the end of the day it's more about seeing how far you can go from weeks zero to week 12, as we say in the syllabus than it is about absolutely ranking all students in this course. So if you're coming into this course among those less comfortable, though a large demographic do not assume that that's automatically putting you in the lower third of the so called distribution. At terms end do I sit down with the TF's and discuss each and every one of the students. We take into account where a student came from, what kind of trajectory they were actually on and so at the end of the day please focus more on, and I don't mean to sound too grand, the process of learning and less on the numeric's. And you'll actually see that we grade problem sets, in particular, very coarsely, whereby along three axis, you will get a score of 1, 2, 3, 4, or 5, where 3, is in fact good. 3 is not C. 3 is good, 4 is better, 5 is best. But more on that as the problem sets are released. So the course's website is where you will find, as in most cases, a whole lot of useful things, if not silly things, too. And we have the luxury, as computer scientists of implementing it ourselves. So over the course of the semester you will see various new features rolling out. You'll find out over the course of the semester that the bulletin board is a wonderful place, certainly in the course of this size, to turn when you have questions about the problem set, questions about some computer science concept. You'll be able to check your grades, download all handouts in advance of lecture typically will I post the slides, if you're the type who wants to scribble on notes. But as you've seen, usually I shy away from long lists of details and more like pictures of cats and other visual cues. So you'll find, too, that we will provide printouts of code when we actually think it particularly advantageous to write right on the paper. Software, videos will be available, usually around 1 to 2 to 3 days maximally after each lecture. So the courses are being filmed and every lecture will go online in various formats including QuickTime and MP3's for downloads to iPods and such. And also you will find a link to download what we call the virtual terminal room, which as you'll see is related to virtual office hours. Books are expensive and in the computer world also not that useful. They are on the shelves of the coop, although we're told that last year they ordered like 120 books for the course and 30 were actually purchased, but this perhaps speak to the fact that there are places like Amazon.com, so if you are the type who actually enjoys the sort of support structure that a book provides, if you like to read up more than say a course's typical materials offer, by all means, procure one or more of the books that we recommend here and discuss more in detail in the syllabus. But realize there are so many resources that this course provides in printed form and electronic form, and my God, there's the whole internet out there. Books are not something that are required for this particular course. Lectures, in general, will be Monday's and Wednesday's, except for this Friday and next Friday, simply because of shopping period and Labor Day. So we'll meet this Friday, next Wednesday, next Friday, but there after this is just a Monday, Wednesday course. So this little visual cue here is to remind me that yes, we do distribute videos in QuickTime formats, MP3's, fun ways that you can, if you're actually this type, maybe in the 14 percent, watch a computer science lecture on your iPod, but it reminded me that at terms end last year, the course culminates in final projects, in which students can design most anything they want, and we actually had some students tackle some iPhone applications. Some one of these at least is now in the Apple store. It's called Rover. It's been adopted essentially by Harvard agencies and it's the iPhone version of the unofficial guide to life at Harvard. They did a brilliant job. I bring this slide up too, just to point out what other technologies might very well be down the road. Some of you may have seen this before, but just to give you a teaser of apparently what's in the pipeline, I thought I would offer this brief distraction here. 

[Muusika]

>> With the MacBook wheel, Apple has replaced the keyboard with a sleek, touch sensitive click wheel. Apple CEO Steve Jobs introduced the product yesterday at the annual Mac Expo. Senior product innovator says the MacBook wheel will make typing a thing of the past. 

>> At Apple our philosophy is create products that are simple to use and nothing's more simple than a single giant button. 

>> Gilman showed me how the revolutionary new computer works. 

>> Gilman: Just open the intuit-type alphabet menu here, scroll to the letter you need and center click to select it and click again to capitalize and repeat this process for each new letter. It couldn't be simpler. You could also let the predictive sentence technology complete the sentence for you. 

>> Gilman says the MacBook wheel has also simplified organization of files, so searching your hard drive will be a snap. 

>> Gilman: Just press both sides of the wheel concurrently and center click and there, you have an alphabetical list of every file on your hard drive. Everything is just a few hundred clicks away. 

>> Apple is calling the MacBook wheel the most intuitive product every designed. 

>> Here at Apple we like to think that we're giving customers features they don't even know they want yet. 

>> While the MacBook wheel won't hit the shelves for another 3 to 15 months, many apple users already have it on their wish list. 

>> I'll buy almost anything [inaudible] and made by Apple. 

>> Alex [inaudible] was one of the lucky few to get to try out a MacWheel and spent 45 minutes typing an email to his friend. 

>> I never really realized how much I hated keyboards until I saw this thing. 

>> I like how it automatically says, sent with a MacBook Wheel, so people automatically know you have one. 

>> With a price tag of just under 2600 dollars for the lowest end MacBook Wheel, it is an investment. But the super thin laptop features numerous innovations, like the new ultra thin hummingbird battery, which can power the MacBook Wheel for a fill 19 minutes before needing to be recharged and the computer is virtually unbreakable unless dropped or hit. But Apple isn't resting on its laurels, Bryan Gilman says they're already hard at work on the next generation of the MacBook Wheel, which will be four ounces lighter due to its lack of streaming hard drive or wheel. For the Ugly news Network, I'm Jeff Tate. 

>> Thank you for that, Jeff. It remains to be seen if the wheel will catch on in the business world where people use computers for actual work and not just dicking around. Moving on, police warn. 

>> David: So I've seen that thing at least a half a dozen times now, including once at like two a.m. last night and I was scrolling down on YouTube and literally like an hour prior, some guy in all seriousness posted, just a wheel? That's the stupidest product I've ever seen. 

[ Laughter ] And then the rants ensued in the thread thereafter. So besides lectures there are also sections and it is your teaching fellow and the course's course assistants that you will get to know very well over the course of this semester. Sectioning won't begin for a week or so's time. More on that in the lectures to come. But know that the course will have several different tracks of sections, much like First Knight's has for music. Sections targeted more at those less comfortable, those more comfortable and those somewhere in between. And we also offer most Sunday nights before a problem set is due on the following Friday is what we call code walkthrough's where one of the course's teaching fellows will lead a session targeted specifically at the week's problem set and will help you answer the question where do I begin, how should I approach this? And that too will be filmed and made available online and always linked on the course's website. So this course has a huge staff. Our staff is larger than Harvard's average class size. We have over 50 people involved in the production of this course on a weekly basis. Some of them teaching fellows who hold sections, grade work, hold office hours and more. Course assistants who are former students, who are offering on a volunteer basis in fact multiple hours of office hours in the computer lab per week. System administrators, folks doing all of our AV and video production. Someone who will actually be taking notes for you. So it is actually my opinion that scribbling down almost every word that someone like me says is not a very good use of one's time. It's much more interesting I think to actually engage with what's on the screen, what's being presented. And so what we will do as a course is post PDF's online within a couple of days of lectures of scribe notes, which is essentially an authoritative version of course notes, unedited, but documenting what went on in lecture that day, thereby hopefully freeing your minds and pencils from jotting information down. We have some of our team here. Most of our team is actually shopping courses. But if a few of your guys would like to come on stage for a moment with our head teaching fellow and assistant head teaching fellow. Allow me to ask the latter to say a quick hello. And as these guys come up in absentia allow me to say that also on staff this year besides the folks you see here are Alex, Alice, Andrew, Batul, Charlotte, Chris, Dan, Dan, Daniel, David, David, David, Derek, Dev, Didi, Doug, Drew, Erica, Fil, Glen, Greg, Janice, Jason, Jean, Jeff, Jesse, John, John, Jonathan, Jordan, Josh, Karim, Kelly, Ken, Kent, Kyu Bok, Lee, Madhura, Marta, Matthew, Michael, Michelle, Mike, Mike, Nathan, Patrick, Peter, Peyton, Rose, Saba, Sanjay, Shannon, Stacey, Ted, Wellie, Yair and me. So our course is teaching fellows and course assistants, Cansu and Yuhki, would you like to say a quick hello? 

>> Hi. It's definitely a great honor to be back here for the third time. And if you're one of those who are like less comfortable. 

[ Laughter ] I think I can [inaudible]. Okay. 

[ Laughter ] If you're one of those [inaudible]. There's no need to be afraid. I walked in here two years ago with no experience what so ever, and I thought that I was like dumb and I was sure that I was going to fail the class. And I came back for the third time. I did not fail the class. This course is great because it has such a good community. As you can tell by the names listed by David. All the CA's and TF's are here to help you. So if you have any questions at all, just come up to us. Not taking this class because it's hard is not a good excuse. So, hi. 

>> [Inaudible]. 

>> Hi, so well both as a student and TF, I've really enjoyed being a part of this course. And even though it's a course that requires a lot of work from you, we've put a lot of work in to it for you as well to make it as enjoyable and as fun as possible. So, we really hope that all of you stay and take part in this very special experience. 

>> Thanks. 

>> David: So you will find, thank you, all of you, you will meet them in the hallway in just a few minutes as well. So you'll find that this course, perhaps more so than many is very much a shared experience. This is not a competitive course. This is not your premed course. This is a course which ultimately yes is about doing independent work, as you'll see each week by way of the problem sets. But you can't help but to get close to someone when you're fighting with some bug and banging your head against the computer screen proverbially to try to track down some bug. And I think you'll find that past students will concur that you exit this course with a lot of friends among students and also on staff. So where does that happen? Well, within office hours in the basement of the science center there's some large computer labs and we pretty much take them over five nights a week. These won't start for some time, and this, to be honest, is perhaps the most beautiful picture of the science center I've ever seen. 

[ Laughter ] It does not look like that on the inside. But it is a place where a good percentage of students do choose to spend time to get one on one assistance with each of the week's problem sets. Each week we will offer more than 100 hours of assistance one on one in the science center per the schedule that will eventually go online. And for those of you who live, say in the quad, or in Mather, or who just don't want to trek all the way to the science center to ask that quick question, we also offer what are called virtual office hours, much like remote technical support where you'll be able to log into a glorified chat room, in which yes, you can type back and forth with a TF or a CA, but you can also share your screen or share control of your mouse with them subject to your consent so that they can help you troubleshoot any problem or any question you have remotely. To give you a sense of what's involved in the course, these are statistics from last year. So you will, I think it's quite fair to say, work your ass off in this course. But per my promise from the start, this is one of those experiences that I don't think a typical student regrets. If you flip through, for instance, the Q Guide forms that are all on the course's website, you'll find that only by putting in the time to a course like this do you really exit having felt like you got something out of it and frankly might very well even have emerged even smarter. So what does it mean to actually write programs and implement problem sets? Well, the first problem set last year, a quick retrospective here, was to implement your very own programming scratch. And we spend just the first week there, and the goal is to implement your own game or animation or art or anything that appeals to you. In week one, then do you implement some basic C programs to get acclimated to some more traditional programming environments at the command line, at Linux so you get comfortable with some of these basics that will certainly serve you well in the long run. Last year's Problem Set 2 was about cryptography. We gave students the opportunity to implement some ciphers, some algorithms that let them encrypt information. And we also offered some students the opportunity to do the opposite. Each problem set, many problem sets, as you'll see are implemented in two editions. A standard edition that we expect almost everyone to do, say 90 percent of the class. And then a hacker edition, which presents the material from a more sophisticated angle, expects perhaps a bit more clever work for those more experienced, and for this one did those students get handed in the hacker edition pre existing user names and passwords in encrypted form and they had to figure out what those passwords for. We actually got into trouble for this a few years ago because all of the sudden FAS Computer Services saw like 50 people running a crack program on nice.fas.Harvard.edu, so they now have been given a heads up for programs like that. Last year students implemented the game of 15. Not all that much fun to play as a party favorite, moving the numbers up down, left, right, but a real stepping stone to implementing something interactive that involves a human and the hacker edition for this one had students implementing God mode, which actually solved this thing for the human, maybe cheat mode is the more apt term, in Sudoku, which was a step up toward that, where we provided the students, you, with a framework with a whole bunch of code that you needed to first understand before taking things the final mile and implementing some of the remaining functionality. And then we dabbled in forensics and this grew out of a real world experience between me and a friend. For this problem set last year, this buddy and I, who he being a particularly good photographer, strolled around campus and we shot photographs of unique, non obvious, but identifiable places on campus. And this was using his digital camera. All of these JPEGs got stored on a digital flash card or what not. And then I accidentally formatting the thing, or erased it. Well, it turns out formatting something or erasing something, usually means neither. It just means doing a little bit of work to make the human think their data has been erased, when in reality it hasn't. It's just been forgotten. And so we tasked last year's students with writing a program in C to actually recover these photos for my friend. We gave everyone a forensic image, so to speak, a big file representing that compact flash card, and they had to recover the several dozen photographs. And they also had to solve this little murder mystery. We provided folks with this image here. Those of you who've seen this before might be doing that squinting thing right now where you're trying to look through the picture, well you look pretty awkward, because this is not a magic eye puzzle. This is just random red noise that actually has behind it an actual message. And it turns out, I think it was Colonel, let's see, I've got my little solution here. Last year it was Colonel Mustard in the study with the candlestick. And this was the murder message recovered by students who wrote code to do so. And then in Problem Set 6 last year. We challenged students with implementing the fastest spell checker possible. What do we mean by that? Well, we handed the students a big text file containing 140 plus thousand English words, and we said write a program that loads all of these words into memory, but very quickly and very efficiently can tell us yea or nay, is this document perfectly spelled or are there errors? And what we provided was a testing framework, a harness, that students, if they wanted to compete, could run their code against some benchmarks, against some testing programs that we wrote. And then, ranked on the course's website from fastest to slowest were the running times, the amount of time it took for each student's code to actually execute, complete opt in. It's by no means required. And we took a bullet for the team and made sure that one of our own teaching fellows intentionally, I think, was at the very bottom of the list. So, there was definitely a lower bound. But the odd, the funny thing was we saw this in the cue guide evaluation, this problem set of all things, was apparently the one that people sunk the most time into. Not because it took any longer than all the other p sets, but they would come back from like dinner, look at the board, and realize dam my friend, my roommate just ever so slightly inch higher than me and so it incentivized people if only to one up their friends and roommates. In Problem Set 7, last year, we asked students to implement their own E*Trade like website, whereby you had to create a website using that language call PHP a database called mysql that actually lets people log in and then manage a portfolio of stocks, buy stocks quote unquote, sell stocks quote unquote, get stock quotes. And from where? Well, we have the students; we had the student patch into Yahoo Finance where they grabbed merely the Real time stock quotes to actually simulate the process of buying and trading stocks. Unfortunately some students, perhaps some economics majors or just folks with too much free time figured out last year how to gain the system. So, even though we gave everyone 10,000 virtual dollars, I think our winner turned teaching fellow this year actually, right don't push them away make them one of your own, for a billion dollars something like that ridiculous. Turns out we weren't really checking whether or not people were trading after hours. And it turns out that also, Yahoo stalk quotes are not in fact perfectly Real time which means if you just have a real E*Trade account you can see the future and see where the stocks are going. 

[ Laughter ] So, apparently you can exploit that if you put your mind to it. and then, in Problem Set 8, the course's final problem set last year, we had students implement a mash up where they take Google News and Google Maps and mash them together using JavaScript, PHP and SQL in such a way that they had a website that they could find all of the local news from whether it's zip code 02138 or 90210. And, you would actually pull the local current even articles by this thing called XML and integrate it into the view of a Google Map. And then, at very course's end was the true climax of the course. This course culminates in final projects, which ultimately will be your opportunity to design your very own piece of software, designed by you or two or three friends. And the course then climaxes with the new and improved, with the second annual computer science 50 fair which last year was an exhibition across the street in one of the engineering buildings with 300 laptops atop tables, popcorn was popping, music was playing, stress balls with CS50's logo were being thrown around. And this was an opportunity for our 300 plus students to exhibit their final projects not only to each other but also to some 900 attendees in total. And we also invited some recruiters as well. So, that is what you have to look forward in this course. You also have cake to look forward to in the hallway. This is CS50 and we'll see you on Friday. 

[Aplaus]

==== Transcribed by Automatic Sync Technologies ====