Introduction to the intellectual enterprises of computer science and the art of programming. This course teaches you how to think algorithmically and solve problems efficiently. Topics include abstraction, algorithms, data structures, encapsulation, resource management, security, software engineering, and web development. Languages include C, Python, SQL, and JavaScript plus CSS and HTML. Problem sets inspired by real-world domains of biology, cryptography, finance, forensics, and gaming. Designed for concentrators and non-concentrators alike, with or without prior programming experience. 68% of CS50 students have never taken CS before.

Class Notes

Students may simultaneously enroll in CS50 and another course that meets at the same time, watching CS50’s lectures anytime online and attending the other course in person. To do so, students should enroll in the other course via and then email to have CS50 manually added to their crimson carts as well. The Ad Board has already granted this exception for CS50; no other steps are required. CS50 is ordinarily graded SAT/UNS, though students taking CS50 to fulfill old Gen Ed requirements or whose concentration requires letter grades should change their grading status to letter-graded by the term’s fifth Monday. First years may take both CS50 and a freshman seminar SAT/UNS. All students are expected to attend an orientation meeting either on Tue 9/11, 4:30pm–5:45pm, in Northwest Science B103 or on Wed 9/12, 6pm–7:15pm, in Science Center D; students with conflicts may watch online. Required sections to be arranged. See for FAQs.


You are expected to

  • watch all lectures,
  • attend all sections,
  • submit nine problem sets,
  • take one quiz, and
  • submit a final project.


CS50 is ordinarily graded Satisfactory/Unsatisfactory (SAT/UNS), much like freshman seminars and some tutorials, though students taking CS50 to fulfill old Gen Ed requirements or whose concentration requires letter grades should change their grading status to letter-graded via my.harvard by the term’s fifth Monday. Even though first years may not ordinarily enroll in both a Freshman Seminar and another non-letter-graded course in any one term, they may take both CS50 and a Freshman Seminar SAT/UNS.

Whether taking the course SAT/UNS or for a letter grade, you must ordinarily submit all nine problem sets, take one quiz, and submit a final project in order to be eligible for a satisfactory grade unless granted an exception in writing by the course’s heads.

Final grades are determined using the following weights:

Problem Sets 60%
Quiz 20%
Final Project 10%
Engagement 10%

Problem sets and the final project are evaluated along axes of correctness, design, and style, with scores ordinarily computed as 3 × correctness + 2 × design + 1 × style. Engagement takes into account attendance at sections, attendance at office hours, participation in the course’s online discussion forum, and/or other forms of engagement. Scores are normalized across teaching fellows and comfort levels at term’s end, so mid-semester comparisons among students of scores are not reliable indicators of standing.

Know that CS50 draws quite the spectrum of students, including “those less comfortable,” “those more comfortable,” and those somewhere in between. However, what ultimately matters in this course is not so much where you end up relative to your classmates but where you, in Week 10, end up relative to yourself in Week 0.

Each student’s final grade is individually determined at term’s end. Remarkable effort and upward trending are considered, as is input from the teaching fellows. The course does not have pre-determined cutoffs for final grades. The course is not graded on a curve. Those less comfortable and somewhere in between are not at a disadvantage vis-à-vis those more comfortable.

Simultaneous Enrollment

Ordinarily, you may not enroll in courses that meet at the same time or overlapping times. However, you may enroll in CS50 and another course whose meetings overlap fully or partially with CS50. To do so, enroll in the other course via, and then email to have CS50 manually added to your Crimson Cart as well. You do not need anyone’s permission or signature, and you do not need to petition the Administrative Board.


No books are required or recommended for this course. However, you might find the below books of interest. Realize that free, if not superior, resources can be found on the course’s website.

C Programming Absolute Beginner’s Guide, Third Edition
Greg Perry, Dean Miller
Pearson Education, 2014
ISBN 0-789-75198-4

Hacker’s Delight, Second Edition
Henry S. Warren Jr.
Pearson Education, 2013
ISBN 0-321-84268-5

How Computers Work, Tenth Edition
Ron White
Que Publishing, 2014
ISBN 0-7897-4984-X

Programming in C, Fourth Edition
Stephen G. Kochan
Pearson Education, 2015
ISBN 0-321-77641-0


CS50 ordinarily meets in Sanders Theatre on Fridays from 9am until 11:45am but will occasionally, when announced, start later than 9am (but still end on time). Students without conflicts are encouraged to attend all lectures in person; students with conflicts may watch later online.

A schedule of lectures, subject to change, appears below.

Week 0 Fri 9/7, 9am–11:45am
Week 1 Fri 9/14, 9am–11:45am
Week 2 Fri 9/21, 9:30am–11:45am
Week 3 Fri 9/28, 9:30am–11:45am
Week 4 Fri 10/5, 9:30am–11:45am
Week 5 Fri 10/12, 9:30am–11:45am
Week 6 Fri 10/19, 9:30am–11:45am
Week 7 Fri 10/26, 9:30am–11:45am
Week 8 Fri 11/2, 9:30am–11:45am
Week 9 Fri 11/9, 9:30am–11:45am
Week 10 Fri 11/16, 9:30am–11:45am


Lectures are supplemented by weekly, 75-minute sections led by the teaching fellows. Different sections are offered for those less comfortable, those more comfortable, and those somewhere in between.

Attendance at sections is expected.

Office Hours

Office hours are opportunities for help with problem sets alongside the course’s teaching fellows and course assistants.

A schedule of office hours appears on the course’s website.

Each week, the instructors will offer additional time to discuss any and all of students’ questions, comments, and concerns about the course or computer science more generally. These dates and times will appear on the aforementioned schedule.


For students who avail themselves of the course’s other resources but still find themselves struggling, the course offers tutoring, to the extent possible, providing opportunities for students to work with the course’s staff one-on-one or in particularly small groups. To arrange, contact the course’s heads.

Problem Sets

Nine problem sets are assigned during the semester. Late work is not ordinarily accepted, except in cases of emergency.

A schedule of problem sets appears below.

Problem Set Language Released Due
Problem Set 0 Scratch Fri 9/7 Tue 9/11, 11:59pm
Problem Set 1 C Fri 9/14 Thu 9/20, 11:59pm
Problem Set 2 C Fri 9/21 Thu 9/27, 11:59pm
Problem Set 3 C Fri 9/28 Thu 10/4, 11:59pm
Problem Set 4 C Fri 10/5 Thu 10/11, 11:59pm
Problem Set 5 HTML, CSS Fri 10/12 Tue 10/16, 11:59pm
Problem Set 6 Python Fri 10/19 Thu 10/25, 11:59pm
Problem Set 7 Python, HTML, CSS Fri 10/26 Thu 11/1, 11:59pm
Problem Set 8 SQL, Python, HTML, CSS Fri 11/2 Thu 11/8, 11:59pm


Due by noon on Thu 11/15 is a take-home quiz that will cover Weeks 0 through 8 (and Problem Sets 0 through 8). The quiz is open-book: you may use any and all non-human resources during the quiz, but the only humans to whom you may turn for help or from whom you may receive help are the course’s heads.

Final Project

The climax of this course is its final project. The final project is your opportunity to take your newfound savvy with programming out for a spin and develop your very own piece of software. So long as your project draws upon this course’s lessons, the nature of your project is entirely up to you, albeit subject to the staff’s approval. You may implement your project in any language(s) as long as the staff approves. You are welcome to utilize any infrastructure, provided the staff ultimately has access to any hardware and software that your project requires. All that we ask is that you build something of interest to you, that you solve an actual problem, that you impact campus, or that you change the world. Strive to create something that outlives this course.

Inasmuch as software development is rarely a one-person effort, you are allowed an opportunity to collaborate with one or two classmates for this final project. Needless to say, it is expected that every student in any such group contribute equally to the design and implementation of that group’s project. Moreover, it is expected that the scope of a two- or three-person group’s project be, respectively, twice or thrice that of a typical one-person project. A one-person project, mind you, should entail more time and effort than is required by each of the course’s problem sets. Although no more than three students may design and implement a given project, you are welcome to solicit advice from others, so long as you respect the course’s policy on academic honesty.

Extensions on the final project are not ordinarily granted, except in cases of emergency. A Dean’s excuse is required. Lateness of submissions is determined down to the minute by submissions’ timestamps. Submitting more than seven minutes late is equivalent to not submitting at all.

Milestone Date
Pre-Proposal Tue 11/6, 11:59pm
Proposal Tue 11/13, 11:59pm
Status Report Tue 11/27, 11:59pm
CS50 Hackathon Thu 11/29, 7pm – Fri 11/30, 7am
Implementation Thu 12/6, 11:59pm
CS50 Fair Fri 12/7, 12pm – 4pm

CS50 Hackathon

From 7pm on Thu 11/29 until 7am on Fri 11/30 is the CS50 Hackathon, an epic all-nighter during which you can dive into your final project’s implementation alongside classmates (from Yale and Harvard alike!) and staff. If you choose to partake, you’ll be asked to propose three milestones for yourself that evening: a “good” one that you intend to achieve no matter what; a “better” one that you think you can achieve; and a “best” one that you hope to achieve.

Dinner will be served around 9pm, second dinner will be served around 1am, and those still awake around 5am will be treated to breakfast at IHOP.

CS50 Fair

From 12pm until 4pm on Fri 12/7 is the CS50 Fair, an epic display of final projects. Not only is the CS50 Fair a venue at which to see classmates’ projects and demo your own, it is an opportunity to mingle with students, faculty, and staff from across campus as well as recruiters from industry. Attendance is expected of all students.

Also in attendance are popcorn, candy, and a raffle with (fabulous) prizes. Family and friends are welcome to join.

Mental Health

If you experience significant stress or worry, changes in mood, or problems eating or sleeping this semester, whether because of CS50 or other courses or factors, please do not hesitate to reach out immediately, at any hour, to any of the course’s heads to discuss. Everyone can benefit from support during challenging times. Not only are we happy to listen and make accommodations with deadlines as needed, we can also refer you to additional support structures on campus, including, but not limited to, the below.

Financial Aid

CS50 does not require that students purchase any books, hardware, or software. While not required, having one’s own laptop is helpful, particularly for office hours. Students without their own laptops are encouraged to reach out at term’s start to the course’s instructor to discuss possibilities.

Academic Honesty

The 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 the course’s quiz is not permitted at all. Collaboration on the course’s final project is permitted to the extent prescribed by its specification.

Regret clause. 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.

Brink clause. If push comes to shove, and you reach a breaking point this term, particularly late at night, and fear you’re about to commit some act that is not reasonable, you may, up to the last moment before you cross that point of no return, email the course’s heads to say that you see no other way out but invoke this clause. (And then go to sleep!) We will then meet with you and, together, get you back on track. For your honesty and your return from the brink, we will waive any penalty for lateness.

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. The course ordinarily recommends exclusion (i.e., required withdrawal) from the course itself.


  • Communicating with classmates about problem sets’ problems in English (or some other spoken language), and properly citing those discussions.
  • Discussing the course’s material with others in order to understand it better. You do not need to cite this if it isn’t related to the pset, but we encourage citing and note-taking on your discussion anyway.
  • 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 after you have submitted that portion of the pset yourself. Add a citation to your own code of the help you provided and resubmit.
  • Incorporating a few lines of code that you find online or elsewhere into your own code, provided that those lines are not themselves solutions to assigned problems and that you cite the lines’ origins.
  • Reviewing past semesters’ tests and 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, provided you properly cite the help. If it is a classmate, make sure they cite giving the help as well.
  • Submitting the same or similar work to this course that you have submitted previously to this course, CS50 AP, or CS50x. Please include a comment at the top of the file indicating it is a resubmission to eliminate any potential confusion.
  • Turning to the course’s heads for help or receiving help from the course’s heads during the quiz.
  • 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. Cite any such resources, especially if they are related to a pset.
  • Whiteboarding solutions to problem sets with others using diagrams or pseudocode but not actual code. Cite who you discussed with and what you discussed, even if you are doing this in office hours under TA supervision. It helps avoid misunderstandings down the road.
  • Working with (and even paying) a tutor to help you with the course, provided the tutor does not do your work for you and you cite the pset help you receive.

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 the 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 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 the few lines allowed herein.
  • 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.
  • Turning to humans (besides the course’s heads) for help or receiving help from humans (besides the course’s heads) during the quiz.
  • Viewing another’s solution to a problem set’s problem and basing your own solution on it.

Acknowledgement and Authorization

Harvard plans to record audio, photos, and video of Computer Science 50 (CS50) lectures, sections, office hours, seminars, and other events and activities related to CS50 (the “Recordings”), with the aims of making the content of the course more widely available and contributing to public understanding of innovative learning (the “Projects”). The Recordings, or edited versions of them, may be made available to other Harvard students, to students at other educational institutions, and to the broader public via edX, the Internet, television, theatrical distribution, digital media, or other means. It is also possible that the Recordings may be used to make other derivative works in the future. Students may elect not to appear in photos and video used in the Projects and may still participate fully in CS50.

When you submit Problem Set 0, you will need to sign online an Acknowledgement and Authorization in the following form:

I understand that, if I do not wish any photos or video of me to be used as part of the Projects, I should so inform the course’s instructor by emailing within one week of enrolling in CS50. In that event, I understand that I should sit in the designated “no-film” zone of CS50 classrooms and should not walk in the field of view of the cameras. I understand that Harvard will take reasonable steps, with my cooperation, to avoid including identifiable images of me in the Projects’ photos and video shot in classrooms and other course locations after I opt out as just described. I understand that I am free to opt out of the Projects’ photos and video in this way, and that doing so will not affect my grade or my ability to participate in course activities.

Unless I opt out of the Projects’ photos and video as described above and take the steps that will be outlined by the instructor to avoid being filmed, I authorize Harvard and its designees to record and use photos and video of my participation in CS50 and activities related to CS50 (the “Recordings”). I understand and agree that the Recordings may include my image, name, and voice. I also understand and agree that, even if I opt out of the Projects’ photos and video, my spoken name and voice may be picked up by microphones outside the “no-film” zone and may be included in the Recordings.

I understand and agree that Harvard and its designees will have the irrevocable, worldwide right to make, edit, modify, copy, publish, transmit, distribute, sell, publicly display, publicly perform, and otherwise use and make available its respective Recordings and any other works that may be derived from those Recordings, in any manner or medium now known or later invented, and to authorize others to do so as well. I hereby transfer to Harvard any rights, including copyrights, I may have in the Recordings that Harvard makes. I will remain free to use and disseminate any ideas, remarks, or other material that I may contribute to course discussions.

I acknowledge and agree that I will not be entitled to any payment, now or in the future, in connection with the Recordings or any works derived from them. This Acknowledgment and Authorization is a binding agreement, and is signed as a document under seal governed by the laws of the Commonwealth of Massachusetts.

Unless you opt out as described in the Acknowledgment and Authorization, you are agreeing, by attending CS50, that your participation in CS50 and related activities may be recorded and used by Harvard in connection with the Projects without further obligation or liability to you, even if you do not sign any authorization.

If you have any questions about the above, contact