>> Hello this is CS50 my name is David Malan and I will be your instructor this semester; and some of you are here because you saw someone tear a phone book in half at something called Harvard Thinks Big last year; and some of you may be here because you've been using a little tool called HarvardCourses and we just so happened to put CS50 on your shopping list. But whatever your reason for being here this is in fact our introduction to Computer Science; and contrary to what you might have heard or seen or perceived in high school, odds are computer science is not quite what you imagined it to be. First and foremost it is not ultimately about programming even though this is unfortunately the message that's conveyed, but in light of a lot of high school curricula rather, programming is just a tool that computer scientists and engineers and increasingly humanists and folks from all sorts of fields use to actually solve problems of interest to them. The programming aspect is just a means to an end; and so this phone book in my hand is just representative to a problem one person might solve, completely non-digital this one, but very much real world whereby there is some person or something in a large chunk of data here; thousand or more pages of text and I want to find someone like Mike Smith. Now at Harvard Thinks Big I happened to tear into this thing myself and it would seem a little pointless to re-hash that same demo so instead I thought I'd solicit an ideally sufficiently strong volunteer to come on up. You have to be comfy on camera but this is your first chance to say hello to mom and dad on camera. One volunteer, yes come on up what's your name? 

>> Sumit. 

>> Sumit, all right come on up and if you could awkwardly hold this up front here for a moment. 

[ Applause ] 

>> David Malan: So if you want to just hang here for just a moment let's walk through the problem at hand. I'm looking for Mike Smith. There are some thousand pages in this book, and I the human could certainly find Mike Smith every easily, very correctly by starting, if you'll simulate from the front of the phone book on page 1, looking for Mike Smith. I see no Mike Smiths because I'm on page 1 where the A's simply are so I turn to the B's and the C's and the D's and so forth and finally I get to the S's but in the worst case I've looked through 1,000 or so pages. Now you the smart human with just gut instincts probably would not be so naive as to start from the left and work your way forward. What would you do? 

>> Dive right into the middle. 

>> So dive right into the middle so if you would now simulate would a typical human might do, where would you dive in first to find Mike Smith? All right so roughly into the middle (oh this will be over too fast) roughly into the middle and at this point you realize what letter of the alphabet are you on? 

>> Student: L. 

>> David: All right so we're on L so roughly half way through; so the intuitive now is of course that Mike is not to the left of the phone book because that's L and prior, but rather he is to the right so we can literally tear this problem in half--cue tearing--cue tearing. 

>> Student: Are you serious? 

>> David: I am very serious. I need you tear not the page out; I need you to tear this phone book in half in front of 500 of your peers. 

[ Applause ] 

>> David: Excellent. So we've now whittled this problem down into half and so we can literally and dramatically throw half of the problem away. So now we're left with a problem that's but 500 pages large and so what might a human do now to find Mike even more closely? Dive in straight to the half again and so now we end up on what letter? 

>> Student: P. 

>> David: So P so we're getting closer but we're not quite there yet and so we tear this problem in half, whittling that problem down although it is getting a little easier; whittling the problem down further into half and if we do this again and again and again we've gone from 1,000 pages, to 500 pages, to 250 to 125 and so forth; and so after just a few relatively speaking of these page tears we've hopefully found Mike Smith's location; and so in computer science terms we actually say that this algorithm or this process, this program is logarithmic. You might remember vaguely logarithms from high school math and such but what this suggests for us , the computer scientists, is that this is certainly a smarter, a faster algorithm. So put this into perspective, imagine now not a phone book with 1,000 pages but like a search engine's index with say 1 million pages or even bigger, 4 billion pages, which isn't even as many web pages as might be out there so if you have 4 billion of something how many times could you tear a 4 billion page phone book in half, in half, in half until you find the person you're looking for? Anyone? How many times can you tear a 4 billion page phone book in half? It's 33, 32, it's only 32 times and you can check that math at home but here lies the power of algorithmic thinking, of computational thinking as they say. You can take a problem that might be relatively intuitive to solve but when you scale this thing up as is increasingly the case in the web, in large data systems, and so forth, you actually have to now think smart, you actually have to think efficiently and you have to solve this problem effectively. And that is ultimately what Computer Science 50 is going to be about. A big round of applause for our volunteer here. 

[ Applause ] 

>> David: Thank you. We have this one parting gift--just a little legal waiver for the cameras if you would. So let's not put him only on the spot; there's a whole bunch of us in this room and we can actually apply this same idea not to these phone books but actually to other real world problems, there's a whole bunch of people in this room. And frankly it would be incredibly time-consuming and tedious for me, to count this room full of people old school style--1, 2, 3 and so forth. So what do you do when you're a kid and you want to count a little faster than 1 and 2 and 3 and 4 what is the simplest thing you do? So try 2m 4, 6, 8 and that's good right? This is not to belittle that simplicity of the idea; that's wonderful. It literally halves the amount of time it takes to solve that problem but we can actually do better. So I propose this algorithm, this program, this process for counting people in this room. In a moment I'm going to ask you to humor us and stand up but not just yet; and then you're going to each take on the number 1--think to yourself I am number 1. Then you're going to pair off with someone else who's standing next to you, you're going to sum your numbers together and one of you whoever is fastest probably is going to sit down and the other person is going to take on his or her number, the summation of those numbers; and then you're going to repeat and if you follow the logic here in just a few moments, there should be just one of you very awkwardly standing. So if you would everyone stand up, take on the number 1 and go. [Talking and music ] 

>> All right at this point I see 1, 2 lone souls standing; anyone else? 3, all right so you have two partners potentially, 4 of you, this should be easy then. Oh and up there, anyone else need a partner up there? Hence the title of this slide all right so 2, we've got you two paired off? Okay so exchange numbers; okay good half of that problem is gone now we have just these two left. Yes? Oh 3 okay. This is when the addition gets very publically awkward so. 

[ Laughter and Applause ] 

>> Okay 210 and? 

>> Student: 233. 

>> Wow 210 and 233 and the total that the teaching fellows got was 550 give or take so a little take maybe, but let's call it a success. Congrats to yourself here. 

[ Applause ] 

>> So now that might not have felt like the fastest algorithm but think about what you could have done with that algorithm in each iteration, much like the phonebook up front here, you literally split that problem in two because on each iteration roughly half of you were sitting down and then another half and then another half. So even though we might have started with 500 some odd people, it very quickly became a 250 person problem and then a 125 person problem. And so in theory after just 2 or 3 steps you were in order of magnitude farther along in this counting process than I would be because I'd still be on person literally 3 or 4. Now consider suppose a whole another 500 people walk into this room suddenly, now there's 1,000 people. Well how many more steps does this algorithm take? Well here is the power--1. And that's when things really get interesting and so this just hints at the types of thinking that one can derive from the field of computer science and apply either to the field itself of computer science, or whatever domain it is that you are here too study. So where can you actually apply these kinds of tricks? Well a number of you have spent this past week playing with this particular tool which is a project the course has been working on for some time in an effort to make it easier and more social to actually shop for courses. A natural question the first week of school is what are you shopping? Well our goal here was to answer that question for people and then hopefully facilitate friends getting together, shopping courses with each other, for each other, picking up syllabi and thus was born what we dub Harvard Courses. For those unfamiliar this is a website at courses.cs50.net and has the entire Harvard Course catalog in it and what it has at top left as you might see is definitely your Facebook login button. Simply by clicking that link you can then log into your account; and then on the left hand side what appears is a little menu of all of your friends who are also using this tool and you can select any one of them and actually see what that person is shopping. You can search obviously by any of the fields up top by days of the week you want a class; days of the week you don't want a class; grad level or undergrad level, faculty scores that are 4.0 and higher, course overall scores that are 4.0 and higher; and a whole number of other features including synchronization with Google calendar. And this is exactly the kind of project that everyone in this room 11 weeks hence could absolutely tackle as a final project. The pieces that we pulled off the shelf here were ultimately reduced to things like 4 loops and what we'll call functions and what we'll call abstraction; and all these fundamentals that at first glance might have some fairly RK and jargon associated with them. At the end of the day this is all about equipping you with skills and knowledge and understanding with which to take a problem, take a large data set maybe and actually produce something useful--produce a project that is of interest to you. Fun facts for those of you who might have been diving into this application already, I looked through the logs and the statistics that we maintain on the site to get a sense of what's working well and what's not and some fun facts include these--11,782 courses are on shopping list at the moment; 1,384 Harvard Facebook users are actively using this; 607 people have synchronized their shopping schedules with Google Calendar, and for the curious if you want to decide if you are average in terms of how much shopping you're doing, 10 is the average number of courses as best we can tell that a student is shopping and it wouldn't be a fun fact if we also didn't look at the scary fact. The maximum number of courses someone on this campus is shopping this week--not an outlier followed by closely 70, 66, 63 on down so that is quite a lot of shopping to do. So you see a problem like this in the real world; you see a problem on campus you might want to solve. Ultimately you'll end up employing something called programming, the act of constructing, telling a computer to do your bidding. Well what form does this actually take? Well in this course you'll see over the course of the next several weeks a number of languages; because here too is there an interest in takeaway; what language you learn in an introductory course, what languages you know is not so much important as it is understanding how these languages work, learning one or two different types of languages and then very easily can you parlay your skills in a language like C or PHP or JAVA or any other number of languages to others. And so what's really empowering about this particular course is that it ultimately one of the goals is to help you help yourself; so that even if 50 proves to be a terminal course for you, you decide CS is not necessarily for me, you none the less exit this course with a whole bunch of skills and savvy that you can go off and apply wherever it is you're most interested in. In fact I just met a few weeks ago with a former student who is not a computer scientist, not even an engineering student; he's actually pre-med and he was working for some MDs this summer and they had gave him a huge text file containing like tens of thousands of patient records, and tens of thousands of doctor records, and they asked him just one semester ahead of CS50 can you tell us exactly which patients met with which doctors and how many times? All right this is kind of the Microsoft Excel problem from hell here right? Like how can you possibly figure that out with actually compelling a machine to do it for you and sure enough we chatted for a few moments, I kind of gently pointed out well it's kind of like problem 7 last year. And so sure enough he took this really large text file, he wrote a program in a language called PHP that's not even that long, a few lines of code yeah big, ran that big data file through it, imported it into what's called a database which is really just a super fancy version of Microsoft Excel or similar, and then he was able to write lines of code that allowed him to select some patients, select some doctors and look at where the intersection was so that the output for his bosses was exactly the answer they were looking for. It's just not possible to solve some of these problems by hand and this isn't even a domain that's necessarily into the world of CS but speaks to you the applicability of it all. So what does it mean to actually program? Well within the next few weeks we will dive into all sorts of languages but the first one is a little something called Scratch. It turns out that Scratch, a programming language developed by MIT's media lab, provides us with a nice, sort of user friendly graphical environment that thought it might look rather cute, it really is just a pictorial incarnation of the very same ideas we're going to be exploring next week with just a blinking cursor and text. We'll come full circle later in the semester and actually begin to create things just as animated again. Programming in this context boils down to telling the computer what to do. So on the left hand side of this particular languages environment I have some puzzle pieces and they are shaped and colored in a manner that hints out their functionality; any blocks that tell the Cat as we'll see in a moment, what to do something happen to be orange. Anything that tells him to sense something like the user's mouse or the edge of his screen is actually purple in color; and so they're nicely colorized and all this but the one that's adventurous right now is this. It's a little puzzle piece that says when the green flag is clicked and this is kind of like the beginning of a program; when you double click an icon on your desktop this is how something like that is implemented; it's listening for that double click, it's listening for that green flag. I'm going to go ahead and change to this Looks pallet over here. There's a whole bunch of blocks that we'll look at in more fun detail on Friday but I'm going to pick the easiest one here and I'm going to type in this string, "Hello CS50", zooming in say how nice the puzzle pieces are nicely interlocked? And then here is this green flag, I go up here and click, and sure enough hello CS50 and this is a program--trivial though this is, this hints at the relative ease with which you can start wiring your thoughts together, instructing a computer line by line to do something for you; and we can very quickly go from something simple like this to something much more dynamic with a few more puzzle pieces but something that testament to what you can achieve in just a few weeks was implemented by a former student in a prior term. I give you a little animation that was implemented with this programming language in just a night called Raining Men. 

[ Music ] 

[ Applause ] 

>> So what you start to see even in programs like this, that they're actually very methodical underneath the hood and even though at first glance you might think to yourself, "I have never done anything like that, I've never used a program that hasn't been re-informing," if you start to look closely at what's up on the screen, you realize oh if I just focus on one of those singers at first, I first have this sprite as it's called, this animated character, but it's not animated by default much like the cat didn't move and so I need something that we'll call a loop--something that makes this sprite move from side to side but I can't let it go all the way to the edge. As soon as I detect with what we'll call a condition if I'm touching the edge I have to essentially spin around 180 degrees and then continue looping. And so with these basic building blocks, can you build up much more interesting things and they don't have to be static animations like this. You can even implement your own versions of some of the most popular console games today for which I need another volunteer. Yes come on up. What's your name? 

>> Fox. 

>> Fox come on up and for your we have--come on up yep--so the keyboard this time for you we have Scratch, Scratch Revolution. So in a moment you're going to go ahead and hit the spacebar and then as things fall from the screen when they line up with the left arrow, hit the left arrow with a different arrow, hit that arrow and see how good a score you can get. So whenever you are ready hit the space. 

[ Music ] 

>> A big round of applause. Very well done. 

[ Applause ] 

>> So this tune made by one of our former students; but it doesn't have to be something written in Scratch, it doesn't have to be a game or animation it can simply be an incredibly, wonderfully way to spend time. So this is perhaps a site that some of you have spent way too much time on last year, if not in the past week or so, this is isawyouharvard.com. This was made by Tej Toor, an economics concentrator in Mather House, this past year for her final project; and Tej prior to 50 had never programmed before and she found herself completely ill-prepared for final exams as a result of this thing having taken off the night before the CS50 Fair which we'll discuss in just a bit; before which she sent out an e-mail to her house list and bam--a thousand posts later was she scrambling to add features, add functionality or start moderating some of the posts. It was a wonderfully good problem to have this too at the culmination of just a few weeks. So what are the expectations over the course of these few weeks? To attend these lectures in sections--more on that in a moment; to submit 9 problem sets, take two quizzes and ultimately design a final project. A word about grades--you may in fact take this course pass-fail. In fact one of the frankly best things I ever did as an undergraduate was, perhaps fittingly, take this course pass-fail. I was an undergraduate here in 1995 as a freshman, I came in thinking I was going to major in government and sure enough I started off on the track; I'd like history, I'd like government, English, these kinds of things in high school. I knew from the relatively limited set of course offerings that my school had the things I felt I was good at and so I went off on the path. I was curious; I was even a user assistant at the time, I was certainly a geek at the time and yet I had no sense really of what actually went on in a classroom like this. In fact I used to glance in the window at the computer science classes that my high school had that some of my friends were taking, and they just weren't interesting, the problems they were working on were like adding some numbers together and moving a cursor around the screen--it was incredibly underwhelming and it wasn't until I dived into this particular course sophomore year, having only gotten over the threshold of discomfort by filling out a little pink slip like this that said I'd like to enroll in this course pass-fail, but I honestly had the courage to venture out beyond my comfort zone. And five weeks less one day later I decided you know what this might actually be for me and I switched from pass-fail to letter graded status at that point in time. It's an unfortunate thing I think pedagogically at this school that there's really not this mindset, this mentality on campus that actually exploring new waters, perhaps by way of mechanisms like pass-fail is actually the norm; I think it's just not part of the culture here and I also think that there saying in a demographic like this there's perhaps this disinclination to say, especially when you need an instructor's signature I would like to take this course pass-fail, let's you think quite reasonably that your peers might think that maybe you're taking it pass-fail because you can't in fact cut it in a course like this. And this is absolutely not true; it's for the most part the entire freshman year for instance at MIT is taking pass-fail. You can similarly explore your sophomore year and Harvard thankfully does have this mechanism. And so ultimately one of the messages we'd like to send today is that if you are the type who's kind of on-the-fence don't think this is for you, worried about hurting your GPA or anything like that. Realize that there's this wonderful mechanism in place that allows you to put your toe in the water for several weeks no less and then get a sense, and then decide whether or not this is something for you. So you may take this course ultimately via pass-fail or letter grade and I am more than happy to chat with you about the implications and to sign any paper work such as the stack here that you might need. So what are you all like? If history is any indication 72% of the people in the theater have no prior programming experience; despite what you may think and despite the fact that some of you may very well be thinking, odds are I know the least about computers than anyone in here, I'm actually a little scared of my computer. There are lots of other people in this course and there have been lots of other people in this course like you. The chart you see here suggests that 72% of last year's students had zero prior computer science background. Moreover there really isn't a typical student in this course. We asked students as we will this year to describe themselves based on gut instinct early on, do you consider yourselves among those less comfortable with computers or just the mere idea of being in this class? Are you among those more comfortable, have you taken any computer science, were you programming at the age of 10 but you'd actually like to learn a bit about things you don't yet know and challenge yourself with new content or are you somewhere in between? And so the breakdown that we've had in past terms are just under half of the students describe themselves as among those less comfortable just over 10% among those more comfortable, and then with the remaining students are indeed somewhere in between. And what the course has done to accommodate these varying levels of background that come into this course, is we offer not only multiple tracks so to speak of sections, we'll see in a moment that we have different tracts for students less comfortable, more comfortable and somewhere in between, and particularly for those students more comfortable who are coming in with say an AP computer science background, may very well know some of the content on the syllabus but like to push themselves further. Do we offer what we dub packer editions of problem sets which extensively cover the same material but with a more technical sophistication, with more detail, and these are simply options that students in this course can elect as per the syllabus. So there are also an increasing number of women in computer science and particular this course which we are thrilled about. Over the past couple of years there have been record numbers of women enrolling in CS50 specifically up from single digits and 20% range years past; and this is wonderful because we absolutely think despite the faces you may see in high school classes, the faces you may see in industry and the press, it is absolutely a field that is equally accessible to men and women alike so it is 50-50 that we hope to see as a result of that reality before long. So what is it you actually do? As much as I might talk on stage twice a week it turns out that it's really by doing and really by diving in and getting your hands dirty that you really take away the course's lessons. Last year for the pieces that do vary year to year a bit, last year's first problem set challenged students to write their first or maybe second or third program using this environment called Scratch. And after just a few words on Scratch which we'll look at in more detail on Friday will you actually feel that you know what, this is actually very intuitive. Once you know what pieces to look for, what mental constructs to reach for, can you realize all right I want to make some dancing figures go back and forth, I need to loop this way and loop this way and check if I'm on the edge and so forth. You begin to realize that all of these big seemingly complicated pieces of software in websites that you use, if you just hone in on little pieces of them at a time and you realize oh I can do that and oh I can do that. And then really the fun begins when you realize all you have to do is now start wiring these ideas together; wiring these little bite size problems together and so in the end that actually make, per Tej's project, a really impressive whole. And for Problem Set 0, too, those of you might think Scratch kind of imploding since I was 6, well then we'll hand you some of these little logic boards which are a variety of real world sensors you can connect to your Mac or PC and push yourself a little further with interactions, with the real world. In problem set 1 last year we introduced students to C, this is the language we use for a good deal of the course before we transition it or it turns into a web program but you'll implement a number of problems that really get you comfortable in what's called the command line environment for lack of a more friendly sounding term; and an environment called Linux or UNEX and really this is not something that might be as foreign to you in a week as might be right now. We introduce throughout this semester real world problem domains. Last year we challenged students to implement their own encryptions ciphers that's perhaps a common need these days to want to scramble or encrypt, to secure your information; whether it's a credit card, whether it's instant messages, or e-mails; simply any kind of information you don't want people to see--well we talk about how you yourselves in the second week can implement some of these so-called ciphers with which to protect your own privacy and security. The week after we implemented the so-called game of 15, this little party favor where you move the numbers up, down, left or right. In just a couple of weeks can you start implementing things that take input from users; and if you really want to push yourselves with that particular week can you implement what we dub God mode. You can play not against yourself; you can program the computer to play against yourself--you can program the computer to play against you. And so that's a little something for those of you more comfortable. And then Sudoku we did last year where it actually becomes a little more interesting where we start providing students not with a blank slate, but with some distribution code. We hand you a bunch of programming code that we wrote because this is very much the norm in the real world. You're not going to start for the rest of your life if you ever need to solve a problem with a computer from scratch, odds are you're going to reach for some off the shelf packages or libraries or tools that other people wrote so that people like us don't have to reinvent the wheel again and again. What do I mean by wheel? If you want to get some input from the user, my God I don't want to have to program it to low level zero and 1 just to get keys from the keyboard; please let there have been someone who does that for me and indeed there are an increasingly sophisticated options that you can pull off the shelf. In problem set 5, last year I took a stroll around campus with one of the teaching fellows with his digital camera, we shot photographs of identifiable but non-obvious spots on campus and then like an idiot I always seem to erase my compact flashcard accidentally. But no matter, I spent a year in graduate school doing forensic research and working for the local Middlesex DA's office where I learned how to make a so-called forensic image of a digital camera's media card. And so we do this very much real world, we grab all of the 0's and 1's that have been erased or mangled somehow by my mistake, I then hand that to every student in the class a file that contains all of those 0's and 1's and they're then challenged to recover those jpegs by writing a program from the start of those 0's and 1's to the end of them, looking for the patterns that it turns out identify these things all of you know as jpegs or photographs that you probably everyday upload or look at on sites like Facebook and the like. It turns out they're relatively simple to find even when they've been deleted whether accidentally or in some cases intentionally--that too is part of the job undeleting things that people had deleted. And then we hand you 140,000 English words in the form of a big text file much like our aspiring pre-med students in recent months, and we challenge you to implement the fastest spellchecker possible. We challenge you to use little RAM, memory as few CPU cycles to write your program as fast as possible and the funny thing here is, is that this tends to be historically the piece that students put the most time into; not at all because it requires the most time; not at all because it's the hardest or anything like that, but because we add on an often basis those sufficiently comfortable with the idea of displaying their name on the course's website you can choose to show your running time; show the amount of RAM you're using on the course's homepage, and it's this fascinating pedagogical motivational tool where you do this. You then go to dinner, you come back and you realize that your roommate has now vested you by five seconds and three hours later you've inched ahead again so it's a wonderfully motivational tool; and speaks to just how addictive frankly this stuff was and that too for me. And this may or may not be the case for you yourself, but one of the realizations I had in college when venturing beyond my comfort zone engulfed toward these waters of CS was wow like there's no cliche. Like homework for me at the time was actually fun and there is some addictive about this; and I even asked Tej during last year's final exam period. And then toward the end of the semester do we transition away from this lower level language known as C and certainly Scratch to things more familiar. Towards the end of the semester do we introduce what languages like PHP and SQL, HTML, CSS, to varying degrees, but with them can you implement the same kinds of ideas that you might have in your mind in the context of a web page. And increasingly that is where the human computer interaction is, and so will you be empowered by terms and not to just to make a website per se but to make an application, something that's of interest to you, something that solves problems, something that lets you tell someone through the most electronic means possible that you saw them somewhere on campus. In the case of last year we did hand students some code with which they could write programs that talked to Yahoo Finance, finance.yahoo.com, free website. Turns out they make stock data and the like available essentially via text files or via a simple API application programming interface which will be one of the themes of the course. And with this data, where students were able to implement last year their own E-trade-like website; whereby you have accounts and you log in your hand age of your users 10,000 virtual dollars and with them can they get stock quotes, by stocks, sell stocks and the like, all of this accomplished just after a few weeks time. And last year to did we hand students Google maps, Google news, asked them to mash those two very familiar real world products together so that they had a map of the United States, little markers sprinkled throughout, that indicated exactly where there were current events going on. So how do we get you from for many of you zero to 60 miles per hour after just 11 weeks, well like many courses here is the course structured around not only lectures for conceptual introductions, but sections, office hours and walkthroughs. So in sections where you have the opportunity to work in smaller environments with one of the teaching fellows, in office hours we have an opportunity to work one on one, hands-on in the computer lab or else we're on campus and really get personalized attention when it comes to diving into these problems. And similarly, particularly for those less comfortable, do we offer prior to the start of each week for a new piece at what we dub a walkthrough whereby one of the teaching fellows will literally start on the first page, give you a mental framework for the week's problems and talk about the ideas that it covers, and then walk through the piece set so that you have a roadmap of sorts that you can follow. So that you're not just handed something that's entirely new to you with no idea which direction to go, we actually do set you off on an appropriate path. And towards that end to give you a sense of the size of the support structure in place for this course, this is the size at the moment of CS50's staff inclusive of teaching fellows, course assistants, myself, as well as folks who help with our video production and the like. Course assistants as we use the jargon are alumni of CS50 who return to the course for a couple of hours a week having taken it in prior years, to help you, the newest batch of students, one on one with office hours, with problem sets; and similarly do the CS function as they might in many courses. Office hours tend to happen in this very beautiful place, at least beautiful according to this picture, never quite feels like that when you're walking in to it; but we're very excited to say that one of the directions in which the Harvard School of Engineering which is a relatively new entity on campus has been putting together this summer with four undergraduates on campus social and learning and teaching space; whereby the goal is to actually provide students like yourselves with an opportunity to interact with each other whether it's to work on P sets, talk, relax, and as you'll see game. It turns out that this space to which you'll have access throughout the year dubbed the lounge, has not only white boards and screens for teaching purposes; we may have also slipped in an Xbox, a Wii and the PlayStation which actually does help make homework fun. Thanks to some friends there's a foosball table, there's a candy machine and there's also a cat in the ceiling. So the so-called lounge what you'll be able to find in just a week or so is timed with the first of the office hours if you so choose to join us for them. Also one of the most useful resources you'll find is the course's website; where not only will the obvious be posted like handouts and such, pests in the syllabus, but there will also be a variety of tools that you can turn to over the course of the semester including our own videos. As you can tell from the cameras, the course is in fact filmed for reasons of distance education and your benefit for review; we've been working on this past summer what we dubbed cs50.tv which is our own delivery mechanism for these videos. Though this is always a bit awkward since you're about to see myself seeing myself, we have put together this new and improved user interface this year whereby after a few days time will each lecture be available via the website, and which you'll notice too flanking it on the right hand side will be a complete English transcript of everything that comes up during lecture. And so being computer scientists, being programmers having taken CS50 that we read a little code that synchronizes the words that are highlighted in the screen with the words that though on this very dark screen are coming out of my mouth in your hands; we also thought it would be a little fun just partly because we can, and partly for accessibility purposes for folks who might tune into the course's open courseware material thanks to Google translate, do I now speak nearly fluent Spanish. If you'd like to see me subtitled in Spanish can you actually watch CS50 this year in Spanish and soon two dozen languages? It's imperfect, though the English is quite spot on, I call myself during this lecture a couple of times a major government because gov major didn't quite translate very perfectly. So what can you expect in terms of the preparation and the fundamentals that will empower you ultimately to tackle projects like these? Well this Friday when we start our lucky computer science itself and introduce Scratch, the programming language in an environment we looked at, but also some of the fundamentals that we'll lace throughout the course. In week 1 computer scientists for those unindoctrinated yet, start counting from 0 typically, you may notice the astute that when we did our self-counting exercise I had to number the steps from 1 to 4; it's only because Keynote does not actually let you start at 0 which is perhaps the norm for normal people anyway; but with Week 1 we'll look at C and some of the basics of computer science as they relate to actually manipulating a computer. In Week 2 we'll look at things like cryptography and functions and the tools that by which you begin to assemble solutions to problems; in Week 3 we'll introduce what are generally known as algorithms and data structures; mechanisms by which you can solve problems more efficiently, effectively. What we'll introduce in Week 4 additional lower level details which really interesting about a computer is that there are these very familiar things like RAM and disk space and the like, but it terms out with just a modicum of experience with manipulating the computer by way of programming, can you actually now use that memory as you see fit, put 0's and 1's in data wherever you see fit; and in the case of the forensic problem set even extract it as someone perhaps did not want you to find. For those perhaps familiar with some of the jargon do we introduce what we call link lists and hash tables and tries, increasingly sophisticated data structures, that allow us to solve problems that are much bigger and much more interesting than the very familiar one that we started with here. We transition to actually real world applications later on like a compression--how do you take a huge amount of data and actually whittle it down into something more manageable; something that uses less of your disk space. We then look toward the end of the semester at these languages that you've might have heard of now, the acronyms therefore like HTML and HTTP, PHP and SQL and the like. And then after that we look at what's increasingly trendy and compelling. A lot of the features you yourself use in Facebook these days are very much dynamic. Things are moving and changing without the whole page reloading; when we looked towards the end of the semester at implementing these increasingly dynamic, Ajax enabled websites much like the ones we all use today. But truly the climax of this course is what we've dubbed the CS50 Fair. Towards semester's end you will have the opportunity to choose a project to work on, choose a project that is entirely of your own choice to execute. And waiting for you across the street ultimately will be a whole lot of balloons, a whole lot of candy, family, friends. Last year's event was attended by 1,000 plus attendees and it will be an opportunity for you to really mingle and to conclude the course with a look at your and other friends' projects. But also this year you will see a whole variety of achievements. So though you'll find yourself playing with Scratch toward term's start, playing with C and similar languages toward term's middle, you'll see last year that when you end up producing yourselves and seeing ads for CS50 Fair are all types of problems and applications being solved. This quick list here suggests last year's students implemented Android apps for their phones, Facebook apps, applications for iPhone and iPods; applications for Mac OS; things involving SOS and the like whereby you can actually send text messages to a program you wrote and get back a response, much like you can for those familiar with this other CS50 App called Shuttleboy. The images you'll see are a little something like this--absolutely mesmerizing what will be on each of your screens and oh there is also some popcorn toward term's end. But we will also introduce towards the end of this semester in an effort to really make it okay to stay up all night, will be the first ever CS50 hack-a-thon. This will be optional, given the late hour, this will be probably bean innovation I will completely regret to the night before; but what we will do is model this after an event that happens at MIT quite often, at Facebook quite often; at 9 p.m. there will be served some pizza; at 2 a.m. there will be Chinese food and for anyone left standing at 6 a.m. there will be a field trip to IHOP in the square. What is the goal of these 10 hours? Well partly this is just for fun--this is what computer people sometimes do, intentionally or unintentionally but as also will see a really nice way to culminate the semester and frankly carve out a 10 hour block where you can bite off your final project's implementation surrounded by friends and the course's staff. But if you're the type who prefers to be bed by midnight, that's quite okay too; there'll be plenty of time to work on the project. Why don't we go ahead for those of you who need a bit of a rest bit, let's take a two minute break and we'll resume with just some final thoughts on 50. 

[ Break ] 

>> We are back so a quote that's been on CS50's website for several years now, long enough that we're not actually not sure who first said it; but that really captures we all think the spirit of this course is this one here, "Demanding but definitely doable, social but educational, a focused topic but broadly applicable skills, CS50 is the quintessential Harvard course." Every one of you standing behind me and this is only like half of them, have taken this course or one like it and are here as your support for the entire semester. In particular let me draw your attention to these two folks on the end who's probably come a little close to my microphone to say hello. Cansu Aydede and Yuhki Yamashita, the course's head teaching fellows [applause], and our leaders from Mather House and Eliot House respectively would like to say a little hello to you. 

>> Hello, welcome to CS50. Well I've been taking this course or I've been part of this course for the last three years so every years at Harvard I've been part of CS50 and it's a really special class or organization to be a part of--really a family and I think Cansu will talk a little bit about that. But yeah we're all excited to have you here and we have all sorts of things planned outside of problem sets and we have the Fair and everything that David has been talking about so we're really excited to start so. 

>> Thanks Yuhki, so CS50 is a family. This is what I'm supposed to tell you guys and we're all here to help you out. I am a senior in Eliot House and this is my fourth year getting involved with CS50 and that's the reason why a lot of CS and everybody else comes back on this stage because we all love CS50 and we all love to be a part of this family again; so welcome to the family. And if you have any questions we're here for you. 

>> David: So we're here for you and we asked last year's students for some choice words we could offer to this year's students. There's of course the queue guy but we survey students throughout the term and we asked them a matter of fact what should we communicate to this semester's student body. Perhaps a mistake with some of the answers we got but one of our choice favorites was this one and it's actually fairly worth drawing one's attention to and that's this: I planned on taking the class as a freshman then convinced myself otherwise because I couldn't fit it into my workload. Same story for sophomore, same story for junior year, I finally took it senior year because they wouldn't get another chance even though it still doesn't fit in the workload ha ha. So I pulled this one out of our archives because of precisely that reason. It's very easy to get caught up in one's own studies here; and even I freshman year, dove into a world very much familiar to me--a world that I did like but I just didn't realize that there were in fact worlds that I loved well beyond my domain of familiarity. In a few moments we will adjourn to the transept where cake happens to await. For those who don't know what this cake means--fix this in post production. In a moment we will adjoin to the transept where cake awaits and in just a few quotes will you actually see a picture of said cake, but we thought we'd paw off a few quotes who tend to have appeared on campus at some websites familiar to you. This one was among our favorite--"I was you at the CS50 Fair; I went to your station to see your program, you were my best friend; but when our hands touched as you handed me a Smiley face sticker, my heart skipped a beat. There's a lot of love in CS50." Some folks on this particular website are a little more to the point. "I saw you at the CS50 Fair; you were with your friends, wearing a tight white polo looking hawt." And this one too, "I saw you walking around the CS50 Fair with a name tag that said you were in the class. You were smart and adorable and all this time I assumed you were dumb and adorable. You just became so much hotter." So in a moment a cake much like this awaits. If you don't know why you're about to eat cake like that you will soon, but you know this. My path in life was fundamentally altered by just a handful of courses at this place and this was in fact one of them. There will in fact never be a good time to try something new, and there will actually never be a semester where you do have that more time. So we do hope that you bear that in mind as we continue this discussion on Friday. This is CS50. 

[ Applause ] 

[ Music ]