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Problem Set 1: C

1. Who is Spotting Whom It turns out it s quite easy to integrate such things into a website these days Tej happens to be using the Google Chart API a free library of sorts to generate those visuals http code google com apis chart If curious documentation for bar charts specifically lives at http code google com apis chart docs gallery bar charts html We actually use a similar service the Google Visualization API for HarvardEnergy a CS50 App with which you can explore Harvard s energy consumption and greenhouse effects http energy cs50 net Select your own dorm or house via the drop down menus at top left to see all sorts of interesting data Here s what else you can do with that particular API http code google com apis visualization documentation gallery html Suffice it to say by term s end you ll be empowered to implement ISawYouHarvard and HarvardEnergy alike 25 Fs Or will we Okay we won t 15 lt 19 This is CS50 Harvard College Fall 2010 For the moment though we re confined to a command line environment But not to worry we can still do some pretty neat things In fact we can certainly generate bar charts with ASCII art Let s do it Implement in chart c a program that prompts a user for four non negative integers one for each of M spotting F F spotting M F spotting F and M spotting M after which it should generate a horizontal bar chart depicting thos
2. compiling code perhaps for the very first time Within CS50 s cloud will you have your own home directory i e personal folder in which you ll store all the code that you write The websites you develop for Problem Sets 7 and 8 and possibly your Final Project will also live in the cloud Not sure what all that means Not to worry you soon will We ve taken the liberty of creating an account on cloud cs50 net for you for simplicity your username is identical to your FAS username Because we don t know your FAS password though we ve generated a pseudorandom password for you To find out what it is head to http www cs50 net me and log in with your FAS username and password if prompted You should see the password we ve generated for you among other things Okay at this point in the story you should know your CS50 username and password It s now time to use them Just like you saw me do in Week 1 you re about to SSH to cloud cs50 net which means you re about to log into some server in CS50 s cluster via a protocol or really a program called Secure Shell Even though CS50 has multiple servers so that we can handle lots of users at once your home directory is mounted i e accessible on all of them SSH allows you to access the contents of your home directory as well as run programs via a command line interface CLI in a terminal window which might fee
3. execute the following command gcc o hello hello c In this case o is but a switch for gcc The effect of this switch is to name gcc s output hello instead of a out Let s now get rid of your first compilation To delete a out execute the following command rm a out If prompted to confirm hit y followed by Enter Welcome to Linux and C Story Time O We explored in Week 1 how hard drives and floppies work but computers actually have a few types of memory i e storage among them level 1 cache level 2 cache RAM and ROM Curl up with the article below to learn a bit about each http computer howstuffworks com computer memory htm Odds are you ll want to peruse at least pages 1 through 5 of that article That s it for now Bet this topic comes up again though Recall that style generally refers to source code s aesthetics the extent to which code is readable i e commented and indented with variables aptly named Odds are you didn t have to give too much thought to style when writing hello c given its brevity but you re about to start writing programs where you ll need to make some stylistic decisions 13 Be careful not to transpose hello and hello c else you ll end up deleting your code 7 lt 19 This is CS50 Harvard College Fall 2010 Before you do read over CS50 s Style Guide http wiki cs50 net Style Guide Inasmuch as style is to some extent a matter of pers
4. successfully look for your program in your current working directory by typing the following command ls You should see output resembling the below a out hello c Actually some more details would be nice Go ahead and execute the command below instead ls l More than just list the contents of your current working directory this command lists their sizes dates and times of creation and more The output you see should resemble the below rwx 1 username student 4647 2010 09 10 19 01 a out rw 1 username student 66 2010 09 10 19 01 hello c It turns out that 1 is another switch that controls the behavior of 1s To look up more switches for 1s in the cloud s user manual execute the command below man ls 12 Don t worry if the numbers you see don t match ours 6 lt 19 This is CS50 Harvard College Fall 2010 You can scroll up and down in this manual using your keyboard s arrow keys and space bar In general anytime you d like more information about some command try checking its man page by executing man followed by the command s name Let s now confirm that your program does work Execute the command below a out You should see your greeting Recall that denotes your current working directory and so this command means execute the program called a out in my current working directory Before moving on let s give your program a more interesting name than a out Go ahead and
5. This is CS50 Harvard College Fall 2010 Problem Set 1 C due by 7 00pm on Fri 9 17 Per the directions at this document s end submitting this problem set involves submitting source code on cloud cs50 net as well as filling out a Web based form which may take a few minutes so best not to wait until the very last minute lest you spend a late day unnecessarily Do take advantage of Week 2 s office hours as well as the video of Week 1 s supersection at http www cs50 net sections and the video of this problem set s walkthrough at http www cs50 net psets If you have any questions or trouble head to http help cs50 net Be sure that your code is thoroughly commented to such an extent that lines functionality is apparent from comments alone Goals Get comfortable with Linux Start thinking more carefully Solve some problems in C Recommended Reading Sections 1 7 9 and 10 of http www howstuffworks com c htm Chapters 1 5 9 and 11 17 of Absolute Beginner s Guide to C Chapters 1 6 of Programming in C 0 lt 19 This is CS50 Harvard College Fall 2010 Academic Honesty All work that you do toward fulfillment of this course s expectations must be your own unless collaboration is explicitly allowed in writing by the course s instructor Collaboration in the completion of problem sets is not permitted unless otherwise stated by some problem set s specification Viewin
6. ainders are possible in between those bounds Well there you have it a way of generating a pseudorandom number between O and 1023 inclusive There s a catch though It turns out that by default rand always returns the same number odds are it s 1804289383 the first time it s called in a program in which case your program s always going to be filled with the same number of Skittles That s because per the man page for rana If no seed value is provided the rand function is automatically seeded with a value of 1 A seed is simply a value that influences the sequence of values returned by a pseudorandom number generator PRNG like rand To be clear it s not the first number returned by a PRNG but rather an influence thereon See why we say pseudorandom all the time instead of 8 Recall that to quit man you can hit q 9 lt 19 This is CS50 Harvard College Fall 2010 random Computers can t really generate numbers that are truly random they have to start somewhere How can you override this default seed of 1 Before you call rand call srand with your choice of seed e g 2 srand 2 Better yet call srand with a seed that actually changes over time literally without your having to recompile your code each time you want it to change srand time NULL Never mind what NULL is for now but know that time NULL returns the current time in seconds that s not a ba
7. arguments and you ll be whisked back to home sweet home In any case now execute cd psetl without any tilde You should find yourself back inside pset1 Make sense All you re doing really is opening and closing folders albeit via a command line interface as opposed to a GUI Incidentally that tilde is really just shorthand notation for your home directory s actual path i e location on the server s hard drive Go ahead and execute pwd which stands for print working directory You should see output like home username psetl On a Linux server denotes the root of the hard drive And so the implication here is that there s a directory called home in the root of the server s hard drive inside of which is your home directory and everybody else s inside of which is that pset1 directory that you just created Okay let s get you home You could just execute cd but let s take another route home this time Go ahead and execute cd 6 A Too corny worried as much 4 lt 19 This is CS50 Harvard College Fall 2010 Recall from lecture that a single dot represents your current working directory It turns out that dot dot represents your current working directory s parent directory i e the directory that it s inside of And so if you re in pseti changing your current working directory to takes you back to your home directory In other words if
8. ch is in a directory called pub which is in CS50 s own home directory the shorthand notation for which is cs50 17 lt 19 This is CS50 Harvard College Fall 2010 destination i e the second command line argument already exists else it renames things Just so you know FM lt OO C will remove i e delete foo c Do be careful if you use that command No need to delete any files though before submitting even if you have more than just three files in pset1 If these tips don t help you solve some problem you re having not to worry Email help cs50 net for assistance but be sure to tell us your username and be sure to detail the problem you re having Take care to seek help if you need it well before the problem set s deadline lest you spend a late day unnecessarily we can t always reply within minutes Head to the URL below where a short form awaits http www cs50 net psets 1 If not already logged in you ll be prompted to log into the course s website Once you have submitted that form as well as your source code you are done This was Problem Set 1 18 lt 19
9. d seed unlike some people No need to store the return value of time in some variable first we can pass it directly to srand between those parentheses It s worth noting though that time is declared in time h so you ll need to include that header file too Alright what other puzzle pieces do we need Well your program will need to tell the user what to do for which printf should be helpful And you ll want to allow the user an infinite number of guesses for which some looping construct is probably necessary And you ll also want to get integers from the user for which Get Int declared in cs50 h is definitely handy Okay where to begin Allow us to suggest that you begin by filling skittles c with this code include lt cs50 h gt include lt stdio h gt include lt stdlib h gt include lt time h gt int main void seed PRNG srand time NULL pick pseudorandom number in 0 1023 int skittles rand 1024 TODO 10 lt 19 This is CS50 Harvard College Fall 2010 We ll leave the TODO to you Remember don t try to implement the whole program at once Perhaps start by printing with printf the value of skittles just to be sure that you didn t make any typos Then save your code and quit nano with ctrl x and proceed to compile it with make skittles Recall that this command saves you the trouble of executing gcc directly with its o flag To run your program assuming it comp
10. e values with the first value s bar on top and the fourth value s bar on the bottom Assume that the user s terminal window is at least 80 characters wide by 24 characters tall Best to ensure that your own window boasts at least those dimensions as by dragging the window s bottom right corner as needed Each bar should be represented as a horizontal sequence of 0 or more pound signs up to a maximum of 80 The length of each bar should be proportional to the corresponding value and relative to the four values sum For instance if the user inputs 10 0 O and O the first bar should be 80 pound signs in length since 10 is 100 of 10 O O O 10 and 100 of 80 is 80 and the remaining three bars should be O pound signs in length By contrast if the user inputs 5 5 0 and O each of the top two bars should be 40 pound signs in length since 5 is 50 of 5 5 0 0 10 and 50 of 80 is 40 and the bottom two bars should be 0 pound signs in length Accordingly if the user inputs 2 2 2 2 each of the four bars should be 20 pound signs in length since 2 is 25 of 2 2 2 2 8 and 25 of 80 is 20 And so forth When computing proportions go ahead and round down to the nearest int as by simply casting any floating point values to int s Rather than label each bar on the left as Google does place each label immediately above the corresponding bar you re welcome to output some blank lines for clarity so long as the last 8 lin
11. eek 0 that finding a value between O and 1023 doesn t actually require that many guesses Odds are you can test your program fairly efficiently You can certainly use temporarily a modulus less than 1024 to save even more time just be sure that your final version does pick a number in 0 1023 19 if only it were that easy to make Skittles 11 lt 19 This is CS50 Harvard College Fall 2010 If you d like to play with the staff s own implementation of skittles on cloud cs50 net you may execute the below cs50 pub solutions psetl skittles Time for Change a Counting out change is a blast even though it boosts mathematical skills with this spring loaded changer that you wear on your belt to dispense quarters dimes nickels and pennies into your hand Orso says the website on which we found this here fashion accessory Of course the novelty of this thing quickly wears off especially when some jerk wants to pay for his newspaper with a hundred dollar bill Fortunately computer science has given cashiers everywhere ways to minimize numbers of coins due greedy algorithms According to the National Institute of Standards and Technology NIST a greedy algorithm is one that always takes the best immediate or local solution while finding an answer Greedy algorithms find the overall or globally optimal solution for some optimization problems but may find less than optimal solutions for some
12. enotes your home directory so the above means make a directory called pset1 inside my home directory Now open that new directory or put another way change your current working directory to that new directory by executing this command cd psetl 3 Harvard actually has a site license for SecureCRT which is technically commercial software that Harvard pays for on your and everyone else s behalf But we ll generally recommend PuTTY for Windows users this semester if only because it s popular and free But you re welcome to use any SSH client If you happen to be running some OS other than Mac OS and Windows on your own computer odds are you already know how to SSH But if not simply drop help cs50 net a note for advice Don t omit the space between mkdir and the tilde 3 lt 19 This is CS50 Harvard College Fall 2010 Notice how your prompt just changed to username cloud psetl since you re now inside your pset1 directory It s worth mentioning that you could have just executed cd psetl a moment ago because cd would simply assume that pset1 must be inside whichever directory you re currently in Want to give it a try Go ahead and just execute cd without any arguments as they say You should find yourself back in your home directory as per your prompt s parenthetical username cloud In fact if you ever get lost inside your account just execute cd without any
13. es of your output are the bars and their labels Unlike Week 2 s progress bar you chart need not be animated Consider the sample output below assume that the boldfaced text is what some user has typed username cloud psetl chart spotting F 3 spotting M 4 spotting F 1 spotting M 2 SHWE Who is Spotting Whom M spotting F FE AE aE aE aE AE aE aE AEE aE aE aE EH F spotting M FE AE aE aE ae AE aE aE AE aE aE AE AE aE AE aE aE aE E F spotting F M spotting M EEA If you d like to play with the staff s own implementation of chart on cloud cs50 net you may execute the below cs50 pub solutions psetl chart 16 lt 19 This is CS50 Harvard College Fall 2010 How to Submit In order to submit this problem set you must first execute a command on cloud cs50 net and then submit a brief form online a SSH to cloud cs50 net if not already there and then execute cd psetl If informed that there is no such file or directory odds are you skipped some step s earlier Not a problem we ll help you fix in a moment If the command indeed works proceed to execute this command next ls At a minimum you should see skittles c greedy c and chart c If not odds are you skipped some more steps earlier If you do see those files you re ready to submit your source 27 code to us cs50 pub bin submit pset1 That command will essentiall
14. g or copying another individual s work even if left by a printer stored in an executable directory or accidentally shared in the course s virtual terminal room or lifting material from a book website or other source even in part and presenting it as your own constitutes academic dishonesty as does showing or giving your work even in part to another student Similarly is dual submission academic dishonesty you may not submit the same or similar work to this course that you have submitted or will submit to another Nor may you provide or make available solutions to problem sets to individuals who take or may take this course in the future Moreover submission of any work that you intend to use outside of the course e g for a job must be approved by the staff You are welcome to discuss the course s material with others in order to better understand it You may even discuss problem sets with classmates but you may not share code In other words you may communicate with classmates in English but you may not communicate in say C If in doubt as to the appropriateness of some discussion contact the course s instructor You may turn to the Web for instruction beyond the course s lectures and sections for references and for solutions to technical difficulties but not for outright solutions to problems on problem sets or your own final project However failure to cite as with comments the origin of any code or technique that
15. gative If the user fails to provide a non negative value your program should re prompt the user for a valid amount again and again until the user complies Incidentally do beware the inherent imprecision of floating point values Before doing any math you ll probably want to convert the user s input entirely to cents i e from a float to an int to avoid tiny errors that might otherwise add up Be careful to round and not truncate your pennies 2 By contrast suppose that a cashier runs out of nickels but still owes some customer 41 How many coins does that cashier if greedy dispense How about a globally optimal cashier 3 For instance 0 01 cannot be represented exactly as a float Try printing its value to say ten decimal places with code like the below float f 0 01 prince S 10fi n f Don t just cast the user s input from a float to an int After all how many cents does one dollar equal 13 lt 19 This is CS50 Harvard College Fall 2010 So that we can automate some tests of your code we ask that your program s last line of output be only the minimum number of coins possible an integer followed by n Consider the below representative of how your own program should behave highlighted in bold is some user s input username cloud psetl greedy O hai How much change is owed 0 41 4 By nature of floating point values that user could also have inputted just 41 Were they
16. iles with no errors execute skittles to see how many Skittles there are Wait one second and then run your program again odds are the number of Skittles will differ Then re open skittles c with nano and take another bite out of this problem Perhaps next implement your program s instructions that explain to the user how to play this guessing game What should your program s output be once fully implemented We leave your program s personality entirely up to you but below s one possible design Assume that the boldfaced text is what some user has typed username cloud psetl skittles O hai I m thinking of a number between 0 and 1023 What is it 0 Nope There are way more Skittles than that Guess again 1 Nope There are way more Skittles than that Guess again 1 Nope Don t be difficult Guess again 1023 Nope There are fewer Skittles than that Guess again 42 That s right Nom nom nom Your program should end once the user has guessed right The above design happens to respond to the user s input in a few different ways but we leave it to you to decide how much to vary your program s output Incidentally know that you can generally force a program to quit prematurely by hitting ctrl c For efficiency s sake you might find it helpful to SSH to the cloud twice in two separate windows so that you can keep nano open in one and use the other to compile and test things And recall from W
17. instances of other problems What s all that mean Well suppose that a cashier owes a customer some change and on that cashier s belt are levers that dispense quarters dimes nickels and pennies Solving this problem requires one or more presses of one or more levers Think of a greedy cashier as one who wants to take with each press the biggest bite out of this problem as possible For instance if some customer is owed 41 the biggest first i e best immediate or local bite that can be Description and image from hearthsong com For ages 5 and up 2 http www nist gov dads HTML greedyalgo html 12 lt 19 This is CS50 Harvard College Fall 2010 taken is 25 That bite is best inasmuch as it gets us closer to O faster than any other coin would Note that a bite of this size would whittle what was a 41 problem down to a 16 problem since 41 25 16 That is the remainder is a similar but smaller problem Needless to say another 25 bite would be too big assuming the cashier prefers not to lose money and so our greedy cashier would move on to a bite of size 10 leaving him or her with a 6 problem At that point greed calls for one 5 bite followed by one 1 bite at which point the problem is solved The customer receives one quarter one dime one nickel and one penny four coins in total It turns out that this greedy approach i e algorithm is not only locally opti
18. l pretty retro at first inasmuch as you can only command the computer to do your bidding by actually typing commands But it turns out once you get the hang of it a CLI is a wonderfully efficient interface We ll teach you plenty of tricks along the way Even though CS50 s servers happen to run an operating system called Linux there exist SSH clients i e programs for Mac OS and Windows alike which means you can connect to the cloud from Cloud is a buzzword that s very much in vogue these days It pretty much means cluster of servers managed by someone else that lives somewhere on the Internet The word is new The idea isn t Just sounds sexier than cluster of servers managed by someone else that lives somewhere on the Internet 2f you don t see any such password you re probably just not in our database yet That may be because you re not yet officially registered for the course because we haven t imported your answers to Problem Set 0 s questions yet because there was a typo among your answers to Problem Set 0 the result of which is that a program we wrote overlooked your submission or because we ve made some mistake Simply email help cs50 net to inquire be sure to mention your full name your fas harvard edu address and if you have one your college harvard edu address so that we can investigate 2 lt 19 This is CS50 Harvard College Fall 2010 any computer with an Internet con
19. mal but also globally so for America s currency and also the European Union s That is so long as a cashier has enough of each coin this largest to smallest approach will yield the fewest coins possible How few Well you tell us Write in greedy c a program that first asks the user how much change is owed and then spits out via printf the minimum number of coins with which said change can be made Use Get Float from CS 50 s library to get the user s input and printf from the Standard I O library to output your answer We ask that you use Get Float so that you can handle dollars and cents albeit sans dollar sign In other words if some customer is owed 9 75 as in the case where a newspaper costs 25 but the customer pays with a 10 bill assume that your program s input will be 9 75 and not 9 75 or 975 However if some customer is owed 9 exactly assume that your program s input will be 9 00 or just 9 but again not 9 or 900 Of course by nature of floating point values your program will likely work with inputs like 9 0 and 9 000 as well you need not worry about checking whether the user s input is formatted like money should be And you need not try to check whether a user s input is too large to fit in a float But you should check that the user s input makes cents Er sense Using Get Float alone will ensure that the user s input is indeed a floating point or integral value but not that it is non ne
20. nd below man 3 rand The 3 instructs man to consult section 3 of the server s user manual whereas programs are generally documented in section 1 the default if you specify no number at all functions are often documented in section 3 Per the man page for rand under synopsts the function is declared in stdlib h So you ll want to put include lt stdlib h gt atop skittles c along with include lt stdio h gt as usual The order of such includes tends not to matter but alphabetical is probably good style Also notice that rand returns a value between 0 and RAND MAX It turns out that RAND MAX is a constant a symbol that represents some value that s defined in stdlib h Its value can vary by server and so it s not hard coded into the manual Let s assume that RAND MAX is greater than 1023 How though do we map a number that s between 0 and RAND MAX to a number that s between 0 and 1023 Turns out that modulo operator we saw in Week 1 is useful for more than arithmetic remainders alone Consider this line of code int skittles rand 1024 The effect of that line is to divide the return value of rand by 1024 and store the remainder in skittles What might the remainder be though when dividing some integer by 1024 Well there might be no remainder in which case the answer is 0 Or there might be a big remainder in which case the answer is 1023 And of course a whole bunch of other rem
21. nection Macs tend to come with an SSH client whereas Windows users must download one for free Whatever your operating system head to http www cs50 net resources where you ll find all sorts of resources among them some HOWTOs i e tutorials for SSH Mac users should read the article on Terminal Windows users should read the article on PuTTY Alright ready to give SSH a try Go ahead and SSH to cloud cs50 net using Terminal or PuTTY After providing your username and password you should reach the command line whose prompt where you ll soon be typing commands looks like username cloud where username is your CS50 and FAS username the tilde means that you re currently inside your home directory That prompt or really the program that runs by default when you SSH to a server is called your shell A shell is just an interpreter of commands You type something it does something For instance go ahead and type echo hi followed by Enter Nice The cloud just said hi back It turns out that echo is a program that someone else wrote long ago that takes a command line argument and simply echoes it back You ll soon be using and writing much more interesting programs E Let s now create a directory for Problem Set 1 where your code will soon live Go ahead and execute the command below by typing it and then hitting Enter mkdir psetl Recall from lecture that d
22. onal preference CS50 doesn t mandate that you mimic the styles that you see in lecture and section But we do expect that you model your own style after common conventions You ll find that CS50 s Style Guide introduces you to some of those common conventions Do keep them in mind as you start churning out code Free Candy 1 So one of the best things about Maxwell Dworkin the CS building is the free candy machine in 14 15 the Lounge in room G123 Well that and the cat in the ceiling Do drop by sometime Anyhow there s a whole lot of Skittles Mike and Ike s and M amp Ms in that machine Want to guess how many Skittles Glad you said yes Implement in a file called skittles c a program that first picks a pseudorandom number between 0 and 1023 inclusive and then asks you the human to guess what it is The program should keep asking you to guess until you guess right at which point it should thank you for playing Where to begin Allow us to hand you some puzzle pieces 14 it might have been us who hacked it to be free gt Photograph by Dan Armendariz Actually there s probably fewer now that we ve mentioned the machine s existence 1 To be clear that range includes 1024 integers from and including 0 to and including 1023 8 lt 19 This is CS50 Harvard College Fall 2010 To generate a random number you can use a function called rand Take a peek at its man page by executing the comma
23. s manner before you quit Terminal or PuTTY or put your computer to sleep 7 If not just execute cd by itself and take that shortcut home 8 Nope nothing Note that the 1 is a lowercase L 1 Indeed there s no o or r in passwd Why Eh slightly shorter to type is all If you forget your new password email he lp cs50 net and we ll reset it to your default 5 lt 19 This is CS50 Harvard College Fall 2010 O hai Nano E Back so soon Okay go ahead and SSH to the cloud if you aren t still there Remember how Then navigate your way to pset1 Remember how Once there execute the command below nano hello c Recall that nano is a relatively simple text editor with which you can write code or any text for that matter Proceed to write your own version of hello world It suffices to re type nearly character for character Week 1 s hai1 c but do at least replace O hai world with your own argument to printf Once done with your recreation hit ctrl x to save followed by Enter and you should be returned to your prompt Proceed to execute the command below gcc hello c If you ve made no mistakes you should just see another prompt If you ve made some mistake you ll instead see one or more warning and or error messages Even if cryptic think about what they might mean then go find your mistake s To edit hello c re execute nano as before Once your code is correct and compiles
24. to input 41 though they d get many more coins Of course more difficult users let s call them oh nOObs might experience something more like the below username nice psetl greedy O hai How much change is owed 0 41 Er how much change is owed 0 41 Er how much change is owed foo Retry 0 41 4 Per these requirements and the sample above your code will likely have some sort of loop If while testing your program you find yourself looping forever remember that you can kill your program i e short circuit its execution by hitting ctrl c sometimes a lot We leave it to you to determine how to compile and run and debug this particular program If you d like to play with the staff s own implementation of greedy on cloud cs50 net you may execute the below cs50 pub solutions psetl greedy 14 lt 19 This is CS50 Harvard College Fall 2010 Saw You a Surf on over to http isawyouharvard com where you ll find a website created by CS50 s own Tej Toor 10 as her Final Project last year your source for posting and browsing missed connections Want to let someone special know that you saw him or her the other day Here s your chance We won t know it s you Anyhow once we have your attention again follow the link to Statistics atop the site where you ll find some neat visuals among them a bar chart As of the end of Week 1 here s who is spotting whom
25. y copy your entire pset1 directory into CS50 s own account where your TF will be able to access it You ll know that the command worked if you are informed that your work HAS been submitted If you instead encounter an error that doesn t appear to be a mistake on your part do try running the command one or more additional times The submit program s a bit old and annoyingly flakey But if informed that your work HAS been submitted it indeed has Now if you instead see some message informing you that your code is not where it should be you ll need to fix that before you submit Recall that you can list the contents of your current working directory simply by executing 1s Recall that you can create a directory e g pset1 with mkdir Recall that you can move to and from directories with cd And know that you can rename or move files with mv For instance mv foo bar will rename a directory or file called foo in your current working directory to bar which is handy if you accidentally named bar foo Meanwhile mv foo c psetl will move foo c into a directory called pset1 in your current working directory assuming pset1 already exists else foo c will be renamed pset1 In other words mv moves things if the 6 This one s much shorter than Problem Set 0 s 7 Note that there is no slash between this tilde and cs50 This particular path implies that a program called submit lives in a directory called bin whi
26. you do discover outside of the course s lectures and sections even while respecting these constraints and then integrate into your own work may be considered academic dishonesty All forms of academic dishonesty are dealt with harshly If the course refers some matter to the Administrative Board and the outcome for some student is Warn Admonish or Disciplinary Probation the course reserves the right to impose local sanctions on top of that outcome for that student that may include but not be limited to a failing grade for work submitted or for the course itself Grades Your work on this problem set will be evaluated along three primary axes Correctness To what extent is your code consistent with our specifications and free of bugs Design To what extent is your code written well i e clearly efficiently elegantly and or logically Style To what extent is your code readable i e commented and indented with variables aptly named 1 lt 19 This is CS50 Harvard College Fall 2010 Getting Started VI a Take CS50 Recall that for Problem Set 0 you obtained if you didn t have one already an FAS account With that account can you log on to computers on campus particularly those in Science Center B14 the terminal room where office hours are generally held It s now time to obtain an account on CS50 s own cluster of servers otherwise known as cloud cs50 net on which you ll soon be writing and
27. you now execute pwd you should find that you re indeed back home in home username Make sense Okay how about dot dot dot What does it probably represent Alright make sure you re indeed in your home directory Let s now take a quick look around Go ahead and execute this command ls That command will list the contents of i e the files and directories in your current working directory Because the only thing you ve created so far is pset1 you should only see pset1 However go ahead and re execute 1s this time with a switch a command line argument that influences a program s behavior ls a The a implies all and so this invocation of 1s lists absolutely everything in your home directory including dotfiles files and directories that are normally hidden by default Never mind those dotfiles for now but know that they exist they re generally configuration files Incidentally if you d like to change that default password of yours go ahead and execute passwd When prompted for your login LDAP password provide your current i e default password for the cloud You ll then be prompted for your new password twice be sure to type the same thing both times Okay need a short break Go ahead and execute the below logout Alternatively you can hit ctrl D or execute exit instead You ve just disconnected from the cloud Always best to log out in thi

Problem Set 1: C

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