• Get comfortable with Linux.

  • Start thinking more carefully.

  • Solve some problems in C.

diff pset1 hacker1

  • Hacker Edition plays with credit cards instead of coins.

  • Hacker Edition demands two half pyramids.

Academic Honesty

This course’s philosophy on academic honesty is best stated as "be reasonable." The course recognizes that interactions with classmates and others can facilitate mastery of the course’s material. However, there remains a line between enlisting the help of another and submitting the work of another. This policy characterizes both sides of that line.

The essence of all work that you submit to this course must be your own. Collaboration on problem sets is not permitted except to the extent that you may ask classmates and others for help so long as that help does not reduce to another doing your work for you. Generally speaking, when asking for help, you may show your code to others, but you may not view theirs, so long as you and they respect this policy’s other constraints. Collaboration on quizzes is not permitted at all. Collaboration on the course’s final project is permitted to the extent prescribed by its specification.

Below are rules of thumb that (inexhaustively) characterize acts that the course considers reasonable and not reasonable. If in doubt as to whether some act is reasonable, do not commit it until you solicit and receive approval in writing from the course’s heads. Acts considered not reasonable by the course are handled harshly. If the course refers some matter for disciplinary action and the outcome is punitive, the course reserves the right to impose local sanctions on top of that outcome that may include an unsatisfactory or failing grade for work submitted or for the course itself.

If you commit some act that is not reasonable but bring it to the attention of the course’s heads within 72 hours, the course may impose local sanctions that may include an unsatisfactory or failing grade for work submitted, but the course will not refer the matter for further disciplinary action except in cases of repeated acts.


  • Communicating with classmates about problem sets' problems in English (or some other spoken language).

  • Discussing the course’s material with others in order to understand it better.

  • Helping a classmate identify a bug in his or her code at office hours, elsewhere, or even online, as by viewing, compiling, or running his or her code, even on your own computer.

  • Incorporating snippets of code that you find online or elsewhere into your own code, provided that those snippets are not themselves solutions to assigned problems and that you cite the snippets' origins.

  • Reviewing past semesters' quizzes and solutions thereto.

  • Sending or showing code that you’ve written to someone, possibly a classmate, so that he or she might help you identify and fix a bug.

  • Sharing snippets of your own code online so that others might help you identify and fix a bug.

  • Turning to the web or elsewhere for instruction beyond the course’s own, for references, and for solutions to technical difficulties, but not for outright solutions to problem set’s problems or your own final project.

  • Whiteboarding solutions to problem sets with others using diagrams or pseudocode but not actual code.

  • Working with (and even paying) a tutor to help you with the course, provided the tutor does not do your work for you.

Not Reasonable

  • Accessing a solution to some problem prior to (re-)submitting your own.

  • Asking a classmate to see his or her solution to a problem set’s problem before (re-)submitting your own.

  • Decompiling, deobfuscating, or disassembling the staff’s solutions to problem sets.

  • Failing to cite (as with comments) the origins of code or techniques that you discover outside of the course’s own lessons and integrate into your own work, even while respecting this policy’s other constraints.

  • Giving or showing to a classmate a solution to a problem set’s problem when it is he or she, and not you, who is struggling to solve it.

  • Looking at another individual’s work during a quiz.

  • Paying or offering to pay an individual for work that you may submit as (part of) your own.

  • Providing or making available solutions to problem sets to individuals who might take this course in the future.

  • Searching for, soliciting, or viewing a quiz’s questions or answers prior to taking the quiz.

  • Searching for or soliciting outright solutions to problem sets online or elsewhere.

  • Splitting a problem set’s workload with another individual and combining your work.

  • Submitting (after possibly modifying) the work of another individual beyond allowed snippets.

  • Submitting the same or similar work to this course that you have submitted or will submit to another.

  • Submitting work to this course that you intend to use outside of the course (e.g., for a job) without prior approval from the course’s heads.

  • Using resources during a quiz beyond those explicitly allowed in the quiz’s instructions.

  • Viewing another’s solution to a problem set’s problem and basing your own solution on it.


Your work on this problem set will be evaluated along four axes primarily.


To what extent does your code implement the features required by our specification?


To what extent is your code consistent with our specifications and free of bugs?


To what extent is your code written well (i.e., clearly, efficiently, elegantly, and/or logically)?


To what extent is your code readable (i.e., commented and indented with variables aptly named)?

All students, whether or not taking the course for a letter grade, must ordinarily submit this and all other problem sets to be eligible for a satisfactory grade unless granted an exception in writing by the course’s heads.

Getting Started

Recall that CS50 IDE is a web-based "integrated development environment" that allows you to program "in the cloud," without installing any software locally. Underneath the hood is a popular operating system, Ubuntu Linux, that’s been "containerized" with open-source software called Docker, that allows multiple users (like you!) to share the operating system’s "kernel" (its nucleus, so to speak) and files, even while having files of their own. Indeed, CS50 IDE provides you with your very own "workspace" (i.e., storage space) in which you can save your own files and folders (aka directories). Anyhow, more on all that another time!

Logging In

Head to cs50.io and log into CS50 IDE. Upon logging in for the very first time, you should be informed that CS50 IDE (aka Cloud9, the software that underlies CS50 IDE) is "creating your workspace" and "creating your container," which might take a moment. (If you already have an account at c9.io, which is Cloud9’s own site, drop sysadmins@cs50.harvard.edu a note, and we’ll let you know how to "link" that account.)

Once you see your workspace, which should resemble mine from Week 1, close any tabs that might have been opened for you by default (e.g., Welcome and README.md). Then decide which "theme" you’d like. By default, CS50 IDE is configured with a theme called "Cloud9 Day." If you’d prefer a darker theme, particularly at night, visit Support > Welcome Page, which should open a * Welcome* tab, and then, within that tab, change Main Theme to Cloud9 Classic Dark Theme, and then close the tab. Feel free to poke around other menus as well to get a sense of CS50 IDE’s user interface (UI). No worries if you’re not sure what most of the menus do (yet!). If among those more comfortable or just curious, feel free to uncheck View > Less Comfortable, which will reveal even more options.


Toward the bottom of CS50 IDE’s UI is a "terminal window" (in a tab called Terminal), a command-line interface (CLI) that allows you to explore your workspace’s files and directories, compile code, run programs, and even install new software. You should find that its "prompt" looks like

username@ide50:~/workspace $

where username is your own (automatically assigned) username. Click inside of that terminal window and then type


followed by Enter to ensure that your workspace is up-to-date. It should take just a few moments for any updates to complete. (Be sure not to close the tab or CS50 IDE itself until they do!)


Okay, let’s create a folder in which your code for this problem set will soon live. Toward CS50 IDE’s top-left corner, control-click or right-click ide50, your workspace’s "root", and select New Folder. A new folder called New Folder should appear; rename it hacker1, then hit Enter. (If you misname it or can’t seem to edit its name, control-click or right-click the new folder and select Rename to try again!)

Next, control-click or right-click that hacker1 folder that you just created and select New File. A new file called Untilted should appear; rename it hello.txt and then hit Enter. (If you misname it or can’t seem to edit its name, control-click or right-click the new file and select Rename to try again!) You should see that hello.txt is indented immediately beneath hacker1, which indicates that the former is inside of the latter. If hello.txt doesn’t appear to be inside of hacker1, simply drag and drop the former into the latter.

Double-click hello.txt, and a new tab should appear within CS50 IDE via which you can edit the file. Go ahead and type something simple (e.g., hello or the ever-popular asdf). Notice that an asterisk () should then appear atop the tab, to the left of the tab’s name. That asterisk indicates that your file has changed but not yet been saved. Go ahead and save the file via *File > Save or, more quickly, via command-S (on Macs) or control-S (on PCs). The asterisk should disappear.

Okay, now let’s confirm via your terminal window that the file is indeed where it should be and start to familiarize you with that terminal window’s command-line interface. As before, your terminal window’s prompt should be

username@ide50:~/workspace $

by default, where username is, again, your assigned username. The prompt further indicates that ide50 is the name of your (automatically created) workspace. And it indicates that workspace is the name of your "current working directory" (i.e., the folder that’s currently open within that command-line environment). The tilde (~), meanwhile, refers to your account’s "home directory," in which your workspace directory lives, but more on that another time. Note that this workspace directory is identical to that ide50 icon in CS50 IDE’s top-left corner (inside of which you created hacker1 earlier). A better choice of names for the latter would have been, well, workspace; we’ll fix that soon!

Okay, let’s poke around. Again click somewhere inside of that terminal window and then type


followed by Enter. That’s a lowercase L and a lowercase S, which is shorthand notation for "list." Indeed, you should then see a list of the folders inside of your workspace, among which is hacker1! Let’s open that folder. Type

cd hacker1

or even, more verbosely,

cd ~/workspace/hacker1

followed by Enter to change your directory to ~/hacker1 (ergo, cd). You should find that your prompt changes to

username@ide50:~/workspace/hacker1 $

confirming that you are indeed now inside of ~/workspace/hacker1 (i.e., a directory called hacker1 inside of a directory called workspace inside of your home directory). Now type


followed by Enter. You should see hello.txt! Now, you can’t click or double-click on that file’s name there; it’s just text. But that listing does confirm that hello.txt is where we hoped it would be. (If not, take another stab at these steps or simply ask classmates or staff for some help!)

Let’s poke around a bit more. Go ahead and type


and then Enter. If you don’t provide cd with a "command-line argument" (i.e., a directory’s name), it whisks you back to your home directory by default. Indeed, your prompt should now be:

username@ide50:~ $

To get back into hacker1, type

cd workspace

and then Enter followed by

cd hacker1

and then Enter. Alternatively, you can combine both steps into one by typing

cd workspace/hacker1

followed by Enter. Phew. Make sense? If not, no worries; it soon will! It’s in this terminal window that you’ll soon be compiling your first program!

Hello, C

First, a hello from Zamyla if you’d like a tour of what’s to come, particularly if less comfortable. Note that she’s using the CS50 Appliance, the (non-web-based) predecessor of CS50 IDE, but not a problem. Any code she writes within the CS50 Appliance should work the same within CS50 IDE!

Shall we have you write your first program? Inside of your hacker1 folder, create a new file called hello.c, and then open that file in a tab. (Remember how?) Be sure to capitalize the file’s name just as we have; files' and folders' names in Linux are "case-sensitive." Proceed to write your first program by typing precisely these lines into the file:

#include <stdio.h>

int main(void)
    printf("hello, world\n");

Notice how CS50 IDE adds "syntax highlighting" (i.e., color) as you type. Those colors aren’t actually saved inside of the file itself; they’re just added by CS50 IDE to make certain syntax stand out. Had you not saved the file as hello.c from the start, CS50 IDE wouldn’t know (per the filename’s extension) that you’re writing C code, in which case those colors would be absent.

Do be sure that you type in this program just right, else you’re about to experience your first bug! In particular, capitalization matters, so don’t accidentally capitalize words (unless they’re between those two quotes). And don’t overlook that one semicolon. C is quite nitpicky!

When done typing, select File > Save (or hit command- or control-s), but don’t quit. Recall that the leading asterisk in the tab’s name should then disappear. Click anywhere in the terminal window beneath your code, and be sure that you’re inside of ~/workspace/hacker1. (Remember how? If not, type cd and then Enter, followed by cd workspace/hacker1 and then Enter.) Your prompt should be:

username@ide50:~/workspace/hacker1 $

Let’s confirm that hello.c is indeed where it should be. Type


followed by Enter, and you should see both hello.c and hello.txt? If not, no worries; you probably just missed a small step. Best to restart these past several steps or ask for help!

Assuming you indeed see hello.c, let’s try to compile! Cross your fingers and then type

make hello

at the prompt, followed by Enter. (Well, maybe don’t cross your fingers whilst typing.) To be clear, type only hello here, not hello.c. If all that you see is another, identical prompt, that means it worked! Your source code has been translated to object code (0s and 1s) that you can now execute. Type


at your prompt, followed by Enter, and you should see the below:

hello, world

And if you type


followed by Enter, you should see a new file, hello, alongside hello.c and hello.txt. The first of those files, hello, should have an asterisk after its name that, in this context, means it’s "executable," a program that you can execute (i.e., run).

If, though, upon running make, you instead see some error(s), it’s time to debug! (If the terminal window’s too small to see everything, click and drag its top border upward to increase its height.) If you see an error like expected declaration or something no less mysterious, odds are you made a syntax error (i.e., typo) by omitting some character or adding something in the wrong place. Scour your code for any differences vis-à-vis the template above. It’s easy to miss the slightest of things when learning to program, so do compare your code against ours character by character; odds are the mistake(s) will jump out! Anytime you make changes to your own code, just remember to re-save via File > Save (or command- or control-s), then re-click inside of the terminal window, and then re-type

make hello

at your prompt, followed by Enter. (Just be sure that you are inside of ~/workspace/hacker1 within your terminal window, as your prompt will confirm or deny.) If you see no more errors, try running your program by typing


at your prompt, followed by Enter! Hopefully you now see whatever you told printf to print?

If not, reach out for help! Incidentally, if you find the terminal window too small for your tastes, know that you can open one in a bigger tab by clicking the circled plus (+) icon to the right of your hello.c tab.

Woo hoo! You’ve begun to program!

CS50 Check

Now let’s see if the program you just wrote is correct! Included in CS50 IDE is check50, a command-line program with which you can check the correctness of (some of) your programs.

If not already there, navigate your way to ~/workspace/hacker1 by executing the command below.

cd ~/workspace/hacker1

If you then execute


you should see, at least, hello.c. Be sure it’s indeed spelled hello.c and not Hello.c, hello.C, or the like. If it’s not, know that you can rename a file by executing

mv source destination

where source is the file’s current name, and destination is the file’s new name. For instance, if you accidentally named your program Hello.c, you could fix it as follows.

mv Hello.c hello.c

Okay, assuming your file’s name is definitely spelled hello.c now, go ahead and execute the below. Note that 2015.fall.hacker1.hello is just a unique identifier for this problem’s checks.

check50 2015.fall.hacker1.hello hello.c

Assuming your program is correct, you should then see output like

:) hello.c exists
:) hello.c compiles
:) prints "hello, world\n"

where each green smiley means your program passed a check (i.e., test). You may also see a URL at the bottom of check50's output, but that’s just for staff (though you’re welcome to visit it).

If you instead see yellow or red smileys, it means your code isn’t correct! For instance, suppose you instead see the below.

:( hello.c exists
  \ expected hello.c to exist
:| hello.c compiles
  \ can't check until a frown turns upside down
:| prints "hello, world\n"
  \ can't check until a frown turns upside down

Because check50 doesn’t think hello.c exists, as per the red smiley, odds are you uploaded the wrong file or misnamed your file. The other smileys, meanwhile, are yellow because those checks are dependent on hello.c existing, and so they weren’t even run.

Suppose instead you see the below.

:) hello.c exists
:) hello.c compiles
:( prints "hello, world\n"
  \ expected output, but not "hello, world"

Odds are, in this case, you printed something other than hello, world\n verbatim, per the spec’s expectations. In particular, the above suggests you printed hello, world, without a trailing newline (\n).

Know that check50 won’t actually record your scores in CS50’s gradebook. Rather, it lets you check your work’s correctness before you submit your work. Once you actually submit your work (per the directions at this spec’s end), CS50’s staff will use check50 to evaluate your work’s correctness officially.


Curl up with Nate’s short on libraries and at least two other shorts for this week.

  • What’s a pre-processor? How does

    #include <cs50.h>


  • What’s a compiler?

  • What’s an assembler?

  • What’s a linker? How does



Hello again, C

Before forging ahead, you might want to review some of the examples that we looked at in Week 1’s lectures and take a look at a few more, the "source code" for which can be found under Lectures on the course’s website. Allow me to take you on a tour, though feel free to forge ahead on your own if you’d prefer. Not to worry if your appliance also looks a bit different from mine.

Smart Water

Suffice it to say that the longer you shower, the more water you use. But just how much? Even if you have a "low-flow" showerhead, odds are your shower spits out 1.5 gallons of water per minute. A gallon, meanwhile, is 128 ounces, and so that shower spits out 1.5 × 128 = 192 ounces of water per minute. A typical bottle of water (that you might have for a drink, not a shower), meanwhile, might be 16 ounces. So taking a 1-minute shower is akin to using 192 ÷ 16 = 12 bottles of water. Taking (more realistically, perhaps!) a 10-minute shower, then, is like using 120 bottles of water. Deer Park, that’s a lot of water! Of course, bottled water itself is wasteful; best to use reusable containers when you can! But it does put into perspective what’s being spent in a shower!

water bottles

Write, in a file called water.c in your ~/workspace/pset1 directory, a program that prompts the user for the length of his or her shower in minutes (as a positive integer, re-prompting as needed) and then prints the equivalent number of bottles of water (as an integer), per the sample output below, wherein underlined text represents some user’s input.

username@ide50:~/workspace/pset1 $ ./water
minutes: what
Retry: oh
Retry: -1
minutes: 0
minutes: 10
bottles: 120

No need to worry about overflow, but do ensure that the user inputs a positive number of minutes!

If you’d like to check the correctness of your program with check50, you may execute the below.

check50 2015.fall.hacker1.water water.c

And if you’d like to play with the staff’s own implementation of water within CS50 IDE, you may execute the below.


Bad Credit

Odds are you have a credit card in your wallet. Though perhaps the bill does not (yet) get sent to you! That card has a number, both printed on its face and embedded (perhaps with some other data) in the magnetic stripe on back. That number is also stored in a database somewhere, so that when your card is used to buy something, the creditor knows whom to bill. There are a lot of people with credit cards in this world, so those numbers are pretty long: American Express uses 15-digit numbers, MasterCard uses 16-digit numbers, and Visa uses 13- and 16-digit numbers. And those are decimal numbers (0 through 9), not binary, which means, for instance, that American Express could print as many as 10^(15) = 1,000,000,000,000,000 unique cards! (That’s, ahem, a quadrillion.)

Now that’s a bit of an exaggeration, because credit card numbers actually have some structure to them. American Express numbers all start with 34 or 37; MasterCard numbers all start with 51, 52, 53, 54, or 55; and Visa numbers all start with 4. But credit card numbers also have a "checksum" built into them, a mathematical relationship between at least one number and others. That checksum enables computers (or humans who like math) to detect typos (e.g., transpositions), if not fraudulent numbers, without having to query a database, which can be slow. (Consider the awkward silence you may have experienced at some point whilst paying by credit card at a store whose computer uses a dial-up modem to verify your card.) Of course, a dishonest mathematician could certainly craft a fake number that nonetheless respects the mathematical constraint, so a database lookup is still necessary for more rigorous checks.

So what’s the secret formula? Well, most cards use an algorithm invented by Hans Peter Luhn, a nice fellow from IBM. According to Luhn’s algorithm, you can determine if a credit card number is (syntactically) valid as follows:

  1. Multiply every other digit by 2, starting with the number’s second-to-last digit, and then add those products' digits together.

  2. Add the sum to the sum of the digits that weren’t multiplied by 2.

  3. If the total’s last digit is 0 (or, put more formally, if the total modulo 10 is congruent to 0), the number is valid!

That’s kind of confusing, so let’s try an example with Daven’s AmEx: 378282246310005.

  1. For the sake of discussion, let’s first underline every other digit, starting with the number’s second-to-last digit:


    Okay, let’s multiply each of the underlined digits by 2:

    7•2 + 2•2 + 2•2 + 4•2 + 3•2 + 0•2 + 0•2

    That gives us:

    14 + 4 + 4 + 8 + 6 + 0 + 0

    Now let’s add those products' digits (i.e., not the products themselves) together:

    1 + 4 + 4 + 4 + 8 + 6 + 0 + 0 = 27

  2. Now let’s add that sum (27) to the sum of the digits that weren’t multiplied by 2:

    27 + 3 + 8 + 8 + 2 + 6 + 1 + 0 + 5 = 60

  3. Yup, the last digit in that sum (60) is a 0, so Daven’s card is legit!

So, validating credit card numbers isn’t hard, but it does get a bit tedious by hand. Let’s write a program.

In credit.c, write a program that prompts the user for a credit card number and then reports (via printf) whether it is a valid American Express, MasterCard, or Visa card number, per the definitions of each’s format herein. So that we can automate some tests of your code, we ask that your program’s last line of output be AMEX\n or MASTERCARD\n or VISA\n or INVALID\n, nothing more, nothing less, and that main always return 0. For simplicity, you may assume that the user’s input will be entirely numeric (i.e., devoid of hyphens, as might be printed on an actual card). But do not assume that the user’s input will fit in an int! Best to use GetLongLong from CS50’s library to get users' input. (Why?)

Of course, to use GetLongLong, you’ll need to tell clang about CS50’s library. Be sure to put

#include <cs50.h>

toward the top of credit.c. And be sure to compile your code with a command like the below.

clang -o credit credit.c -lcs50

Note that -lcs50 must come at this command’s end because of how clang works.

Incidentally, recall that make can invoke clang for you and provide that flag for you, as via the command below.

make credit

Assuming your program compiled without errors (or, ideally, warnings) via either command, you can run your program with the command below.


Consider the below representative of how your own program should behave when passed a valid credit card number (sans hyphens), wherein underlined text represents some user’s input.

username@ide50:~/workspace/pset1 $ ./credit
Number: 378282246310005

Of course, GetLongLong itself will reject hyphens (and more) anyway:

username@ide50:~/workspace/pset1 $ ./credit
Number: 3782-822-463-10005
Retry: foo
Retry: 378282246310005

But it’s up to you to catch inputs that are not credit card numbers (e.g., Lauren’s phone number), even if numeric:

username@ide50:~/workspace/pset1 $ ./credit
Number: 7722574501

Test out your program with a whole bunch of inputs, both valid and invalid. (We certainly will!) Here are a few card numbers that PayPal recommends for testing:

Google (or perhaps a roommate’s wallet) should turn up more. (If your roommate asks what you’re doing, don’t mention us.) If your program behaves incorrectly on some inputs (or doesn’t compile at all), time to debug!

If you’d like to check the correctness of your program with check50, you may execute the below.

check50 2015.fall.hacker1.credit credit.c

And if you’d like to play with the staff’s own implementation of credit within CS50 IDE, you may execute the below.


Itsa Mario

Toward the beginning of World 1-1 in Nintendo’s Super Mario Brothers, Mario must hop over two "half-pyramids" of blocks as he heads toward a flag pole. Below is a screenshot.

Super Mario Brothers

Write, in a file called mario.c in your ~/workspace/hacker1 directory, a program that recreates these half-pyramids using hashes (#) for blocks. However, to make things more interesting, first prompt the user for the half-pyramids' heights, a non-negative integer no greater than 23. (The height of the half-pyramids pictured above happens to be 4, the width of each half-pyramid 4, with an a gap of size 2 separating them.) Then, generate (with the help of printf and one or more loops) the desired half-pyramids. Take care to left-align the bottom-left corner of the left-hand half-pyramid, as in the sample output below, wherein boldfaced text represents some user’s input.

username@ide50:~/workspace/pset1 $ ./mario
Height: 4
   #  #
  ##  ##
 ###  ###
####  ####

No need to generate the bricks, cloud, numbers, or text in the sky or Mario himself. Just the half-pyramids! And be sure that main returns 0.

We leave it to you to determine how to compile and run this particular program!

If you’d like to check the correctness of your program with check50, you may execute the below.

check50 2015.fall.hacker1.mario mario.c

And if you’d like to play with the staff’s own implementation of mario within CS50 IDE, you may execute the below.


How to Submit

Step 1 of 2

  1. When ready to submit, log into CS50 IDE.

  2. Toward CS50 IDE’s top-left corner, within its "file browser" (not within a terminal window), control-click or right-click your hello.c file (that’s within your pset1 directory) and then select Download. You should find that your browser has downloaded hello.c.

  3. Repeat for water.c.

  4. Repeat for credit.c.

  5. Repeat for mario.c.

  6. In a separate tab or window, log into CS50 Submit, logging in if prompted.

  7. Click Submit toward the window’s top-left corner.

  8. Under Problem Set 1 on the screen that appears, click Upload New Submission.

  9. On the screen that appears, click Add files…. A window entitled Open Files should appear.

  10. Navigate your way to hello.c. Odds are it’s in your Downloads folder or wherever your browser downloads files by default. Once you find hello.c, click it once to select it, then click Open (or the like).

  11. Click Add files… again, and a window entitled Open Files should appear again.

  12. Navigate your way to water.c as before. Click it once to select it, then click Open (or the like).

  13. Navigate your way to credit.c as before. Click it once to select it, then click Open (or the like).

  14. Navigate your way to mario.c as before. Click it once to select it, then click Open (or the like).

  15. Click Start upload to upload all of your files at once to CS50’s servers.

  16. On the screen that appears, you should see a window with No File Selected. If you move your mouse toward the window’s lefthand side, you should see a list of the files you uploaded. Click each to confirm the contents of each. (No need to click any other buttons or icons.) If confident that you submitted the files you intended, consider your source code submitted! If you’d like to re-submit different (or modified) files, simply return to CS50 Submit and repeat these steps. You may re-submit as many times as you’d like; we’ll grade your most recent submission, so long as it’s before the deadline.

Step 2 of 2

Head to https://forms.cs50.net/2015/fall/psets/1/ where a short form awaits. Once you have submitted that form (as well as your source code), you are done! If you end up resubmitting your files (per step 1 of 1), no need to resubmit the form.

This was Problem Set 1.