Problem: Scratch


  1. Program in Scratch.

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 problems is not permitted (unless explicitly stated otherwise) 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 or writing to others, but you may not view theirs, so long as you and they respect this policy’s other constraints. Collaboration on quizzes and tests is not permitted at all. Collaboration on the 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 your instructor. If a violation of this policy is suspected and confirmed, your instructor reserves the right to impose local sanctions on top of any disciplinary outcome that may include an unsatisfactory or failing grade for work submitted or for the course itself.


  • Communicating with classmates about 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, such 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 years' quizzes, tests, 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 solutions to problems online so that others might help you identify and fix a bug or other issue.

  • 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 problems or your own final project.

  • Whiteboarding solutions to problems 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 before (re-)submitting your own.

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

  • Failing to cite (as with comments) the origins of code, writing, 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 when it is he or she, and not you, who is struggling to solve it.

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

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

  • Providing or making available solutions to problems 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 problems online or elsewhere.

  • Splitting a problem’s workload with another individual and combining your work (unless explicitly authorized by the problem itself).

  • 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.

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

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


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


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


To what extent is your code free of bugs?

To obtain a passing grade in this course, all students must ordinarily submit all assigned problems unless granted an exception in writing by the instructor.


For help with Scratch:

Itching to Program?

Head to and sign up for an account on MIT’s website by clicking Join Scratch atop the page. Any username (that’s available) is fine, but take care to remember it and your choice of password.

Then head to and take note of the resources available to you before you dive into Scratch itself. In particular, you might want to skim the Getting Started Guide.

Next try your hand at Pikachu’s Pastry Catch by (former student) Gabe Walker! Click the green flag and then, per Gabe’s instructions, hit your keyboard’s space bar, at which point the game will begin! Feel free to procrastinate a bit.

If curious, Gabe’s source code can be seen at (You can also full-screen the game at that same URL, as full-screening the embedded game here might not work.)

Next, be sure you know what’s recyclable and compostable these days by trying out this remix of Oscartime by Jordan Hayashi!

Jordan’s source code can be found at (You can also full-screen that game at that same URL.)

If you’ve no experience (or comfort) whatsoever with programming, rest assured that Gabe’s and Jordan’s projects are more complex than what we expect for this first problem set. (Click See inside in Scratch’s top-right corner to look at each project’s underlying "implementation details.") But they do reveal what you can do with Scratch.

In fact, for a gentler introduction to Scratch (and programming more generally), you might want to review some of the examples at Once you can say to yourself, "Okay, I think I get this," you’re ready to proceed.

Now it’s time to choose your own adventure! Your mission is, quite simply, to have fun with Scratch and implement a project of your choice (be it an animation, a game, interactive art, or anything else), subject only to the following requirements.

  • Your project must have at least two sprites, at least one of which must resemble something other than a cat.

  • Your project must have at least three scripts total (i.e., not necessarily three per sprite).

  • Your project must use at least one condition, one loop, and one variable.

  • Your project must use at least one sound.

  • Your project should be more complex than most of those demonstrated in lecture (many of which, though instructive, were quite short) but it can be less complex than Oscartime and Pokemon Go. As such, your project should probably use a few dozen puzzle pieces overall.

Feel free to peruse additional projects online for inspiration, but your own project should not be terribly similar to any of them. Try to think of an idea on your own, and then set out to implement it. But don’t try to implement the entirety of your project all at once: pluck off one piece at a time. Gabe, for instance, probably implemented just one pastry first, before he moved onto the game’s other sprites. In other words, take baby steps: write a bit of code (i.e., drag and drop a few puzzle pieces), test, write a bit more, test, and so forth.

If, along the way, you find it too difficult to implement some feature, try not to fret; alter your design or work around the problem. If you set out to implement an idea that you find fun, you should not find it hard to satisfy this problem set’s requirements.

Alright, off you go. Make us proud!

Incidentally, if you don’t have the best Internet access, you’re welcome to download Scratch’s "offline editor" at But when done with your project offline, be sure to upload it to your account at via File > Share to website in the offline editor.

Once finished with your project, click See project page in Scratch’s top-right corner. Ensure your project has a title (in Scratch’s top-left corner), some instructions (in Scratch’s top-right corner), and some notes and/or credits (in Scratch’s bottom-right corner). Then click Share in Scratch’s top-right corner so that others can see your project. Finally, take note of the URL in your browser’s address bar. That’s your project’s URL on MIT’s website, and you’ll need to know it later.

Oh, and if you’d like to exhibit your project in CS50 AP’s studio for 2017-18, head to, then click Add projects, and paste in your own project’s URL.

How to Submit

Step 1 of 4

In your Scratch project, go to the "File" menu, and click "Download to your computer". Save the file as project.sb2.

Step 2 of 4

Go to, substituting USERNAME in the URL with your own GitHub username. On the left side of the screen, click on "Branch: master". In the field that says "Find or create a branch…​", type cs50/2017/ap/scratch and click "Create branch".

Step 3 of 4

Click the button that says "Upload files". Drag your project.sb2 Scratch file into the box that says "Drag files here".

Step 4 of 4

Click the green "Commit changes" button. You’re done!

Your submission should be graded for correctness within 2 minutes, at which point your score will appear in!


Can’t find the "Branch: master" button.

If you don’t see a "Branch: master" button upon going to your submit50 page on GitHub, click the "README" button next to "We recommend every repository include a…​" and then click the green "Commit new file" button. After that, the "Branch: master" button should appear!

Your submission should be graded for correctness within 2 minutes, at which point your score will appear in!

This was Scratch, your first programming problem in CS50 AP!