CS50 2015 - Week 12

Key Takeaways

[Music] [Music] [Music] [Music] this is cs50 Harvard University [Laughter] [Music] [Music] so if I know Mike is probably in the latter half of the phone work I can now teir the problem in half that was actually real that struggle it stop it stop it stop make it the daylight [Music] hey hey heyyy heyy you humans are so easy to beat all right this is cs50 and this is the start and the end of week 12 and you may recall that in week zero this is the messaging with which we began that it doesn't matter where you end up relative to your classmates but where you today and maybe just a few weeks from now end up relative to yourself some weeks ago and in fact we do hope after so many problem sets and so many hours and a couple of quizzes and still with the final project that you do feel particularly proud having come all the way from week one where this perhaps was the earliest of struggles whether in the standard edition or the hacker Edition thereof and I would propose that at some point in your free time that you go back and see your PHP or JavaScript and see if you can't uh implement this far far faster and more comfortably than you once upon a time did ago indeed after this recall you did you did cryptography you did the game of5 you did forensic uh challenges you did uh the fastest spell checker that you could you did cs-50 Finance the cs50 mashup and then now ultimately your own final project and so today we try to get closure and look at where we've come and where we're going um and just to reassure too that once all of the remaining Training Wheels come off you pretty much have sufficiently many Tools in your toolkit to now go off and do most anything in the world of programming certainly considering taking some higher level course can be of Advantage But realize too even if this is the last CS course you take realize that on Mac OS there's so many different tools that you can use independent of having to use something like the cs50 IDE nearly the same tools exist for Windows for Linux and more and indeed one of the goals in cs50 in in using this fire hose of languages C and PHP and SQL and JavaScript and HTML and CSS is to really make sure that you don't exit this course thinking I learned C but rather that you learned how to program and that you understand a little something about computer science itself in fact even though we haven't looked at all of the following languages it's fun now to enter this community of of folks who who find geeky humor funny and even though some of the languages you're about to see might not be totally familiar you you're at least get a few Chuckles from at least one familiar language JavaScript this was a talk by a particularly uh well first programmer some time ago entitled W and we thought we would give you a glimpse at how computer scientists tend to think or at least talk all right good you guys know what w means w exactly exactly let's talk about Ruby uh in Ruby if you reference an undefined variable of course it name errors as you would expect and if you try to assign uh B to a with them undefined of course it name errors as you would expect and what happens if you try to assign a to a with a undefined n n correct nil W let's talk about Ruby Ruby unlike uh some other Dynamic languages does not have bare words so you cannot just type words in and have strengths come out unless you define uh a particular method missing that does the right thing and then if you type be wordss suddenly Ruby Sports be wordss and in fact it will even sport be wordss with bangs in them uh and this this is not deserving of w this is actually a result of how awesome Ruby is but if you ever actually do this then w let's talk about JavaScript does anyone know in JavaScript what array plus array well let me ask you this first what should array plus array be array empty array I would also accept type error uh that is not what array plus array is wrong wrong array plus array is empty string obviously ly I think that's I think that's obvious to everyone uh now what what would array plus object be this should obviously be type error because those are completely disparate types uh does anyone know what this is uh no close no far away it's object right nicely done now of course because uh this is plus so you can flip the operands and the same thing comes out so if we do what no that's just an object uh if you do object plus array should get exact same thing which as you can see you do and finally uh the only one of these that's actually true is uh because you know you add arrays you get empty string that doesn't make sense but an object plus an object is actually not a number technically so this one's actually right and uh exactly right like what is even going on in this La I just I don't even understand why what person with a brain in their head would think that any of this is a good idea okay okay enough making fun of languages that suck let's talk about JavaScript if I say array. new 16 uh or just array 16 I get an array of 16 things which it represents as 16 commas which is obvious and uh if I then join those with a string then I get the string 16 times this is actually the only line in this entire presentation that's reasonable uh now if I take that string and then add a one to it it interprets the one as or cast the one to his string and then we get W one a bunch of times fine does anyone know what will happen if I subtract one from the string I'm assuming no one does let me I'll give you a hint does does this help does anyone know yes [Laughter] wet [Applause] man that's all I got thank you [Applause] guys let's take a quick look at some of the things I had for you so the cs50 hackathon is this epic all nighter during which you and your classmates from y will dive into hopefully not begin your final projects uh the evening will begin at 7:00 p.m. first dinner will be roughly at 9:00 p.m. second dinner will be at 1: a.m. and then for those Still Standing breakfast will be served at IHOP around 5: a.m. uh you might see such scenes as this uh as promised in week zero this year we'll have not only food and dinner and Candy but also for the second time in history vegetables um but around 3 or 4 a.m. scenes like this are not all that uncommon indeed we see our fair share of pillows being brought to the hackathon which is fine as well and then the climax of the course is the so-called cs50 Fair there's one both here and in New Haven a week after the one at Harvard is Monday uh December 7th during the afternoon in Northwest science and upon arrival you will check in and you will see such things as popcorn and balloons and ultimately as of last year over 2,000 people coming to see your final project students staff and faculty from across campus and even off- campus and if it weren't enough incentive to come see uh you yourself um realize that your friends can be encouraged to come to see Asana and eBay and Facebook and Google and Microsoft and paler and core and others recruiters and alumni from these various companies to talk about life in the real world opportunities both full-time and uh summertime uh in the actual industry and if that weren't reason enough to come see you uh your friends can be encouraged to enter the raffle uh whereby upon arrival uh you as students will each be handed a bunch of smiley face stickers and attendees like your friends will be handed a little raffle card upon arrival and for every person they chat up they will be handed by you a smiley face sticker Each of which represents a uh entry into a PRI a raffle with fabulous prizes among them an Xbox a wi and a whole bunch of other fun things some of which we've seen here in class so stay tuned for that but ultimately it's entirely about the accomplishments this semester and the expressions and excitement that you will stir in those attending where you ultimately are wearing your very own uh this I took cs50 t-shirt like that here so do encourage your friends to head to this URL here which will send you to all details therefore meanwhile if you're considering another look at computer science this spring or Beyond um realize that this is the same handout albeit updated since week zero that we handed out and if you go to the middle of this booklet there's copies in the transcept outside um realize this shows you via arrows exactly what courses you can go off to explore this spring next fall summertime um and Beyond so do take a look at the chart therein to get a sense of things and if you'd like to get involved in other capacities do know if you don't already that the College Board which you may have some not so fun memories of is nonetheless just creating a new curriculum framework called AP Computer Science principles some of you who might have taken or at least heard about an existing CS course at high schools uh called apcsa which is a fairly mundane class that focuses way too much on the language Java and the mechanics there of apcs principles meanwhile will be more about ideas and more about problem solving and toward this end we a bunch of our friends at UC Burkley e code.org and a few other entities around the world are creating curricula that will satisfy apcs principles which is to say that cs50 AP will be a uh AP equivalent that students in various high schools across the world can take starting this coming fall 2016 and if you'd like to get involved in secondary school education and involved in this Outreach do reach out to us there whether you're a TF a CA or simply interested in education at large and indeed if you'd like to join cs50's own team realize that as soon as terms end and as soon as term ends we'll begin recruiting for teaching fellows course assistants as well as the many artists that make this um course possible POS behind the scenes um creating its online assets its inperson opportunities and more so if any of these roles here appeal do let us know at this URL here now in a little while we'll Jour to just as we did in week zero some cake uh this time it'll be downstairs in the pub so head there later on um but I did just want to take a moment to recognize um really what this cake here represents or perhaps more e canonically what this here face off um represents it has truly been an honor honestly um to be partnering with our friends down the road in New Haven this semester it's certainly been a strange thing uh an unusual thing dare say an unprecedented thing for two colleges to be coming together offering one course in the same on two different campuses and bringing these two student bodies together but it's been such an honor to work with Andy with scaz and with Jason in New Haven and the entirety of our 44 person staff of teaching assistants and course assistants in New Haven who for the first time in y history were mostly themselves undergraduates indeed until this year fall 2015 Yale did not actually have a tradition or an allowance for undergraduates leading sections and serving as teaching fellows much like we've enjoyed here within computer science at Harvard for sometime and so that alone has been an extraordinary opportunity for us to partner with them on that initiative and bring into the fold um such leaders as Andy and other teachers there on campus um and allow me to draw special attention too to this fellow in the middle even though he now lives in New Haven um largely because we sent him there um this is all the result of Jason heror having been a teaching fellow for cs50 for quite a few years here year graduated last year uh Kirkland house and ultimately um I think got a phone call from me at one point that pretty much reduced to hey would you mind moving to New Haven after graduation um this was all because we were trying to stand up this initiative and we wanted to make sure that there was there was institutional knowledge down there in New Haven because we were building something for Scratch and if Jason if you could maybe just come on up awkwardly toward stage so we can at least all see Jason heror in person come on surely without Jason um Gail 50 would not have been possible so our thanks to Jason heror and also we have we have a huge staff that we won't draw personal attention to everyone here but over a hundred individuals here in New Haven who make this course possible and you may just see your own teaching fellow on this list whether here or in New Haven and so for we could um a huge round of applause for the entirety of the teaching staff [Applause] and let me draw some special attention to a few of the folks here especially Hannah and Maria and Davin and Rob who has the course's heads make everything run here in Cambridge of course Colton Ogden who begins most of our lectures over there on music um Doug Doug Lloyd uh who this is cs50 AP who is leading our AP initiative Dan Armand DARS who without whom we would not have a cs50 IDE this year aise who makes everything possible behind the scenes including running the lights as pictured here and then last but not least um cs50's production team um suffice it to say it's cs50's production team that empowers so many of us uh to sleep in in the afternoons and to engage with the course's material really asynchronously and this is very much one of the design goals of the course as you know we uh are enjoy right now an opportunity to allow simultaneous enrollment we have an opportunity for students certainly to watch these courses uh materials online even in real time live right now um and this is entirely because of the production team that you see or even don't see around you and behind you here for instance this was some footage shot by Jordan this past year just to speak to the sort of artistry that goes on behind the scenes this of course is Foo in the quad and just to give you a look back at week zero this was with uh the imagery with which we began the first [Applause] [Music] week that was from cs50 Zone Jordan and also behind the scenes here today is Ramon and Ian and Scully and Dan arm Dan coffee Dan coffee who who heads cs50's production team and truly over the past several years this is my ninth year involved with the course really has Dan coffee with the production team taken cs50 to another level not only do we shoot the course now in 4k so to speak this coming year we'll also be able to shoot it in 6K um as well as in virtual reality um partly because it's cool um partly because it's cool but also as you know we have a very sizable online community folks who for various reasons could not travel to or could not attend a place like Harvard and Yale and one of the goals pedagogically is to experiment with new forms of technology so that we can through proxy and through you all give online students around the world an opportunity to see and feel and hear what a place like Harvard or Yale feels like so coming soon in Fall 2016 and now to take it down a notch um this is about to be horrifying but you might recall that most of the lecture videos this year or every other ends with a sort of seemingly strange clip from Seinfeld inspired by some actual Episode reimplemented by cs50's production team who've been incredibly gracious and creative um and I thought I would show you one of The Inspirations a 30- second clip from an actual Seinfeld show that inspired one of this semester's I'm told favorite Clips so first an actual clip from Seinfeld come on who's dancing want me to want me to get it started okay [Applause] [Music] hold up fancy Moses so we often talk about pushing students beyond their own Comfort zones um I now am going to crawl up into a ball ball and Saab as we play for you this reimplementation of this thanks to cs50's production [Music] Team all right who's dancing come on who's dancing you want me to get it started I'll get it started wo [Applause] FC Moses and now and now some special than for an alumna who is now doing her PhD just down the road here at Harvard and who can most often be seen in this form in office hours both in Cambridge and in New Haven in fact if we enhance a big round of applause for cs50 Z Zila and now a word from cs50 staff in both locations who would like to offer some parting words of their own there is no other course in which everyone who works for the course is as excited to be there and like be involved in it as cs50 I don't know it's like this really like important and special responsibility um and like kind of an incredible experience and I'm really glad I get to be a part of people's education CS5 in my opinion is amazing I love it um I loved it when I was taking the class and I love it even more as a TF tfing is a lot of work but it's really rewarding because you get to teach so much you really get to know your students you get to know the material yourself and you get to just watch them become computer scientists my students are the highlight of my my semester I been my life I been my life on you I been my life and this is s 50 I've just never felt as as much like a leader on campus um as I had this semester this is one of the only opportunities uh On's campus to really get uh invested in teaching it's really cool to see CS from the other side I was surprised at how excited all the students were it's also nice when like people like recover like a picture of Rick ay and are like who is that yeah I wanted to give back because I got a lot of support when I was a student all you need is enthusiasm and um a love of or CS or any of the above and you'll be able to do it all my all my students keep Rick Rolling me I did my I did my life on you I been my life I been my life I been my life on you [Applause] [Music] it's been so much fun to like teach about this thing that I like really love and think it's a lot of fun and like try to get other people excited about it as well I'm analia Ernst and this is [Applause] [Music] cs50 and now you may recall that we began the semester talking ultimately about computational things and solving problems independent of actual programming languages and we thought we'd see just to what extent this has sunk in by trying an exercise we didn't do in week zero but we thought we'd try a couple of times here in week 12 uh for which I need a volunteer who's comfortable coming up here on stage come on up what's your name yon come on up this Ray and if you all if you have a sheet of paper from us or a blank sheet of paper of your own um go ahead and take that out at this point nice to meet you all right yong's um goal here is going to be the following I have here a drawing that only she is going to be able to see come on over here in the middle if you'd like and let me give you a microphone here and your goal here is going to be to describe in as precise detail as possible what you see and these folks here as the sort of computer implementers of this need to draw exactly what you say and then what I'll do is grab a few random samples from the audience and we'll see just how precisely this worked out so I describe this you describe this you tell your hundreds of classmates here exactly what to draw go okay so in the very middle of the piece of paper there are two shapes um one on top of the other but not touching but like almost touching so there is a circle on the top and a square on the bottom and they're almost the same size they're like kind of medium small and within the circle there is a uh there are two there are three um squares so there's a little square within a bigger square and within a bigger Square square and within the square on the bottom there are three circles a little circle within a bigger Circle within a bigger Circle got that so why don't you I'll go walk around I'll grab a few and if you want to recap for those who need a second pass okay so do you need me to like explain this again okay all right so in the middle of the sheet of paper there are two uh shapes and one is on top of the other but they're roughly the same size there is a medium small circle on top of a medium small uh Square okay so like it's kind of like on top like think about putting it like a snowman but like with two different shapes instead of two circles and then on the inside the circle there is a small box inside of another small box inside of another small box and inside of the square there's a small circle inside of another small circle inside of another small circle did that make sense yes a lot of pressure all right I will be right back going through the audience here okay very nice thank you okay we got to take that one all right all right that seems like a good random sample thank you all right so now also awesome oh awesome okay so awesome stay right there I'm going to go ahead and reveal to you what some of your classmates here did so here we have uh this one here okay it sort of just keeps going and going um here a little different interpretation okay um here let's see getting closer albeit smaller oh that was very nice though I just had to grab this one what was the actual answer let's take a look over here what she was describing was this image here so men some of many of you up here in the ones I look did get this right let's go ahead and Sh Let's uh let's call someone else up and see how easily or more uh with what level of difficulty they can do it thank you so much how about one other volunteer a little farther back okay I saw this hand first come on up what's your name Mar oh sorry Mar Marcy come on up nice to meet you all right here we have microphone for you let me get a drawing and so if you want to just use the flip side of that sheet or some other sheet of paper I'm going to go ahead and give Marcy a different one here that only she can now see that only she can see opaquely okay okay go draw 16 little dots um all in a grid so um four rows of four dots each um and the dots are Hollow so they're like tiny little circles oh they're five of them okay it's oh it's five so it's five rows of five dots um five rows of five dots and then start on the top left corner okay so um five rows of five dots and the dots are Hollow so they're like tiny little circles actually so they're like white on the inside okay so five rows of five dots and then and then start from the top left Dot and then draw a line down to the next Dot down and then draw another line um to the one to the right of that one so that's two lines so far and then draw a line down to the next one down okay so that's three lines down right and then down and then left and then down okay so um so recap it's the first one is down okay you're starting from the top left corner and then down and then right and then down down and then left and then down and then right and then right and then left okay so we're about halfway through you said right then left oh oh whoops okay it's not easy okay um let's start over let's start over from the top left corner all right one more pass yeah okay down right down left down right right down right up right up left left up up right down right up and you should be on the top right corner okay all right and if you did that correctly you should now have this on your sheet of paper so let me come grab a couple okay thank you thank you thank you okay I don't think you want that um okay oh love this thank you uh sorry to reach wow a okay we'll take just that one all right that's good it's very good all right so let's see what we have here so so notice try to make a mental imprint of this let me go back to the projection here and this is pretty darn good here very nicely done this one a little smaller but I think that's on the right track as well very nicely done um okay this one feel like I shouldn't put this on the internet so let me okay this one has a phone number for some reason thank you uh um and then why don't we end with this one and now thank you so much we have time for one more example here um this time how about uh on the left there come on up yep with your hands yep all right come on up come on up this time though come on up what's your name Daniel Daniel this time though we're going to spice this up a little bit and we're going to have you come over to the touch screen so now this time I'm going to show all of you all the drawing and on the honor System you may not move your eyes ever so slightly up here to see what the actual image is um so you just keep uh just straight ahead and then you're going to draw on this screen what your classmates describe to you and I'll try to summarize verbally so it's loud enough all right so on our system here look straight ahead only and you all step by step not unlike the peanut butter and jelly example let's try to describe this first instruction please draw a big circle draw a big circle all right this so I'm going to undo draw draw a stick figure without arms I heard draw a stick figure without arms okay all right second instruction left arm on hi left arm on hip angular angular angular okay we have to uh let me give you the Eraser let's erase okay again slightly pointy elbow pointy elbow slightly acute elbow slightly acute elbow all right what else third instruction R now rotate the rotate 0 rotate it 90° what right arm is a v right arm is a v nice all right and last step last step line away from the head a line away from the head no top left yeah [Applause] 45 45° angle up no [Applause] yes from from the top left of his head not connected to his head [Applause] yes that's good that's good that's good that's right high right high right High higher at the end of the line line at the end of the line [Applause] right lower ey low I heard [Applause] lowercase yeah that was amazing thank you all right so we have time for just one more exercise um you might recall the following theme music which uh realize we've uh taken some liberties with the rules of the following game because in problem set 8 we asked you a bunch of questions that were essentially in the form of Jeopardy and only after P at 8 did we decide well maybe it would actually be a little more fun to play something else instead so for this we're going to need four members of the teaching staff four members of the teaching staff and four students about one two about three four come come on down come on down all right we're also going to need we're also going to need one student if the staff would like to go here at left students over here right we need someone who's really good at arithmetic Under Pressure okay right here being volunteered by Danya come on up so you'll use the touch screen here what's your name Michael Michael come on up so we'll give you instructions in just a moment but if you want to just write staff on the right and students on the left for scorekeeping let me go ahead and let each of you introduce yourselves to your class on this last day I'm James I'm a freshman hi I'm Aon I'm Maya I'm Catherine and now the teaching staff I'm Jack Abby hi I'm Tim Maria all right so we have in advance come up with a number of questions uh some of whose answers we kind of made up but others of whose answers are based on actual statistics from your own submissions of problem set 8 and other problem sets so in general each of these answers will have surveyed let's say 100 people we will put the top four or five or six answers on the board Each of which has a score associ with it what we're going to do is tweak the rules a little bit so rather than give control to one team or Another We're simply going to use these staples easy buttons that was easy to allow each team to buzz in the quickest and whoever guesses hits the button first and gets a question right we'll potentially get that many points we'll keep going we'll keep going and then whichever team finishes the board will get all of the points tallied thus far so what you'll want to do is tally the points as we go for each question answered right and then once the round ends you're going to put the total either here or over here so I tell in my head or on or on the screen in front of everyone yes or on your phone which is back there apparently all right so we'll walk you through this no need to do anything just yet the first thing the students and the staff need to do is hit their respective buttons the fastest after I start reading the question and you want to propose an answer make sense all right here we go name a function declared in standard io. that was easy staff printf show us printf very nice good answer so if you want just write down 68 or keep tracking your mind of 68 now we're going to move on as soon as I'm going to read the question again you may not buzz in until after I've repeated the question name a function declared in standard i.h same question what is sprintf okay what is s sprintf show us s print F no I'll read it again a function declared in standard io. scan scan F show us two strikes once more a function declared in standard i.h that was easy students F open F open very nice all just keep repeating the question a function declared in standard i.h that was easy staff F close F close good job nice we have two answers left on the board number two and number five for this round a function declared in standard i.h students F re show us F Reed very nice whoever now whichever team answers the fifth and last answer gets all the points so you should be adding all these numbers up and whoever gets this gets that total is there a mistake there is no number six okay no number six unimplemented name a function declared in standard IO staff that was easy oh F right show us F right it explain so much about let's try once more name one name a function declared in stand IO Tim F fsek about one more try name of function declared in F in uh standard i.h F get c f get C so no one gets the points Colton want to show us what number five was okay malok is not in standard io. Jason herar and everybody all right let's move on to the second question first person to buzz in here to this question a program that you use while programming staff clang clang very nice number two answer again name a program you use while programming no just that was easy students uh GDB GDB [Music] so at this point 38 would be the total but no one's gotten any points yet all right name a program you use while programming that was easy ven Valen oh also all right name a program you use while programming students that was easy PHP PHP name a program you use while programming staff face show us show us Facebook we have top six answers on the board three to go name a program you use while programming Google Staff Google Google all Bo all right name two left name a program you use while programming cs50 discuss cs50 discuss one more try a program you use while programming I heard students student students cs50 id cs50 id and last one a program you use while programming that was easy check 50 no let's reveal the answer number six was Spotify all right I think we have time for just one or two more complete the following sentence no uh no points for either team still it's zero to zero winner take all soon good job um complete the following sentence I'm never going to staff give give you up nice students easy let you down let you down around I'm never going run around around and desert you run around and desert you run around desert okay students never got to make you cry make you cry goodby say goodbye step say goodbye I can't believe this is the question question you're all getting them right uh say goodbye yep and the last one students hurt you tell tell a lie and hurt you students get 100 points what that is it for cs50 cake is now served [Applause] [Music] are you crazy what do you think you're doing I'm trying to get into the elevator what are you talking about you didn't see me waiting here I didn't see you waiting man if you didn't see me waiting then why'd you pull your card in like that cuz that's how I get into the elevator production why your camera getting in everyone's way get out I need to go