Syllabus

Instructor

David J. Malan ’99
malan@harvard.edu

Description

Introduction to the intellectual enterprises of computer science and the art of programming. This course teaches students how to think algorithmically and solve problems efficiently. Topics include abstraction, algorithms, data structures, encapsulation, resource management, security, and software engineering. Languages include C, Python, and SQL plus students’ choice of: HTML, CSS, and JavaScript (for web development); Java or Swift (for mobile app development); or Lua (for game development). Problem sets inspired by the arts, humanities, social sciences, and sciences. Course culminates in a final project. Designed for concentrators and non-concentrators alike, with or without prior programming experience. Two thirds of CS50 students have never taken CS before. Among the overarching goals of this course are to inspire students to explore unfamiliar waters, without fear of failure, create an intensive, shared experience, accessible to all students, and build community among students.

Class Notes

This course ordinarily meets for lectures in Sanders Theatre on Mondays, 3pm–5pm, but the course’s first lecture will be in Sanders Theatre on Wednesday, 9/4/19, 3pm–5pm, during shopping period. Students are expected to attend the course’s first eight lectures in person unless simultaneously enrolled in (or, during shopping period, shopping) another course that meets at the same or an overlapping time, in which case they may watch CS50’s lectures online and attend the other course in person. (The Ad Board has already granted this exception for CS50; no other steps are required.) Students with other academic or athletic conflicts should email the course’s heads. After the course’s eighth lecture, all students will watch their choice of lectures (on web development, mobile app development, or game development) online. CS50 is ordinarily graded SAT/UNS, though students whose concentration requires letter grades should change their grading status to letter-graded by the term’s fifth Monday. Students may take CS50 SAT/UNS to fulfill the Science and Engineering and Applied Science distribution requirement or the Quantitative Reasoning with Data requirement, but not both. First years may take both CS50 and a freshman seminar SAT/UNS. Graduate students are welcome to cross-register for CS50. All students are expected to attend an orientation meeting during the second week of term; students with conflicts may watch online. Required sections to be arranged. See cs50.harvard.edu for FAQs, syllabus, and what’s new for Fall 2019.

Expectations

You are expected to

  • attend (or, if simultaneously enrolled in another course, watch) eight lectures,
  • attend eight sections,
  • solve ten problem sets,
  • take seven quizzes,
  • take one test, and
  • design and implement a final project.

Objectives

Educational Objectives

Among the overarching goals of this course, independent of its curriculum, are to

  • inspire students to explore unfamiliar waters, without fear of failure;
  • create an intensive, shared experience, accessible to all students; and
  • build community among students.

Learning Objectives

Among the overarching goals for students individually in this course is that they learn something that we haven’t taught them, as is manifest at term’s end by so many students’ final projects that use languages, libraries, tools, and techniques not taught in the course. Along the way will students learn to

  • think more methodically;
  • program procedurally;
  • represent and process information;
  • communicate succinctly and precisely;
  • solve problems efficiently;
  • recognize patterns among problems;
  • decompose problems into parts and compose solutions thereto;
  • operate at multiple levels of abstraction;
  • separate design from implementation details;
  • infer from first principles how systems work;
  • assess the correctness, design, and style of code;
  • teach themselves new languages;
  • identify threats to privacy and security;
  • read documentation, drawing conclusions from specifications;
  • test solutions to problems, find faults, and identify corner cases;
  • describe symptoms of problems precisely and ask questions clearly; and
  • identify and quantify tradeoffs among resources, particularly time and space.

Ultimately, the course provides students with a foundation for further studies in computer science and empowers students to apply computer science to problems in other domains.

Curricular Objectives

Week 0 # Scratch

  • Problem solving
  • Inputs, Outputs
  • Representation
  • Unary, Binary, Decimal
  • Abstraction
  • ASCII, Unicode
  • RGB
  • Algorithms
  • Running Time
  • Pseudocode
  • Scratch
    • Functions, Arguments, Return Values
    • Variables
    • Boolean Expressions, Conditions
    • Loops
    • Events
    • Threads

Week 1 # C

  • Linux
  • Command-Line Interface
  • C
    • Functions, Arguments, Return Values
    • Variables
    • Boolean Expressions, Conditions
    • Loops
  • Libraries, Header Files
  • Text Editors
  • Terminal Windows
  • Compiler
  • Types
  • Integer Overflow
  • Floating-Point Imprecision

Week 2 # Arrays

  • Preprocessing
  • Compiling
  • Assembling
  • Linking
  • Debugging
  • Arrays
  • Strings
  • Command-Line Arguments
  • Cryptography

Week 3 # Algorithms

  • Searching
    • Linear Search
    • Binary Search
  • Sorting
    • Bubble Sort
    • Selection Sort
    • Insertion Sort
    • Merge Sort
  • Asymptotic Notation
    • O
    • Ω
    • Ɵ
  • Recursion

Week 4 # Memory

  • Pointers
  • Segmentation Faults
  • Dynamic Memory Allocation
  • Stack
  • Heap
  • Buffer Overflow
  • Data Structures
  • File I/O
  • Images

Week 5 # Data Structures

  • Linked Lists
  • Trees, Binary Search Trees
  • Hash Tables
  • Tries
  • Abstract Data Types
  • Stacks, Queues

Week 6 # Python

  • Python
    • Functions, Arguments, Return Values
    • Variables
    • Boolean Expressions, Conditions
    • Loops
  • Modules, Packages

Week 7 # SQL

  • SQL
    • Tables
    • Types
    • Statements
    • Constraints
    • Indexes
    • Keywords, Functions
    • Transactions
  • Race Conditions
  • SQL Injection Attacks

Grades

CS50 is ordinarily graded Satisfactory/Unsatisfactory (SAT/UNS), much like freshman seminars and some tutorials, though students whose (potential) 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 still meet all expectations 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 50%
Quizzes 10%
Test 20%
Final Project 10%
Attendance* 10%

* At lectures and sections.

Problem sets and the final project are evaluated along axes of correctness and style, with correctness ordinarily counting for 75% of your score and style counting for 25%. 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 end up relative to yourself when you began.

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

You 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.

Ordinarily for simultaneous enrollment, you need the permission of the other course’s instructor, you need to arrange for “compensatory instruction,” and you need to petition the Administrative Board itself. But the Administrative Board has already granted an exception for CS50 itself, which obviates those needs. You do not need anyone’s permission or signature, and you do not need to petition the Administrative Board.

To simultaneously enroll in CS50 and another course that meets at the same or overlapping time, all that you need to do is enroll in both courses via my.harvard. CS50 is deliberately listed in the catalog as having no day or time (even though it does ordinarily meet on Mondays, 3pm–5pm) so that it doesn’t technically conflict with any other courses.

Books

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.

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

Lectures

Attendance at the course’s first eight lectures is expected unless you are simultaneously enrolled in (or, during shopping period, shopping) another course that meets at the same or overlapping time, in which case you may watch CS50’s lectures online and attend the other course in person. After the course’s eighth lecture, all students will watch their choice of lectures (on web development, mobile app development, or game development) online.

If you have some other unavoidable academic or athletic conflict, simply contact the course’s heads to discuss.

# Lecture Date Location
0 Computational Thinking, Scratch Wed 9/4, 3pm–4:15pm Sanders Theatre
1 C Mon 9/9, 3pm–5pm Sanders Theatre
2 Arrays Mon 9/16, 3pm–5pm Sanders Theatre
3 Algorithms Mon 9/23, 3pm–5pm Sanders Theatre
4 Memory Mon 9/30, 3pm–5pm Sanders Theatre
5 Data Structures Mon 10/7, 3pm–5pm Sanders Theatre
6 Python Mon 10/21, 3pm–5pm Sanders Theatre
7 SQL Mon 10/28, 3pm–5pm Sanders Theatre
8 Privacy Fri 11/1, 10:30am–11:45am Sanders Theatre
9 Students’ Choice    
10 Students’ Choice    

The course’s final two lectures will depend on your choice of tracks.

Supersections

Supersections are optional Zoom-based opportunities after each lecture to review the day’s material and ask additional questions.

Supersections will begin in Week 1.

Sections

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.

Sections will be assigned in Week 1. Sections will begin in Week 2.

Tutorials

For additional help with problem sets, you may optionally sign up for one or more tutorials per week, Wednesdays through Saturdays. An amalgam of tutoring and office hours, tutorials are led by the course’s teaching fellows and course assistants.

Tutorials will begin in Week 1.

Office Hours

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

Office hours will begin in Week 1.

Problem Sets

Problem sets are programming assignments that allow you to implement each week’s concepts in code.

# Language Deadline
0 Scratch Sun 9/8, 11:59pm
1 C Sun 9/15, 11:59pm
2 C Sun 9/22, 11:59pm
3 C Sun 9/29, 11:59pm
4 C Sun 10/6, 11:59pm
5 C Sun 10/13, 11:59pm
6 Python Sun 10/26, 11:59pm
7 SQL Sun 11/3, 11:59pm
8 Students’ Choice Fri 11/15, 11:59pm
9 Students’ Choice Fri 11/22, 11:59pm

Code Reviews

Code reviews are optional Zoom-based opportunities after each problem set for feedback on the design of your code.

Quizzes

Quizzes are short assignments due after each lecture that allow you to apply each week’s concepts to new problems. Each quiz is open-book: you may use any and all non-human resources during a quiz, but the only humans to whom you may turn for help or from whom you may receive help are the course’s heads.

# Deadline
1 Tue 9/10, 9am
2 Tue 9/17, 10:30am
3 Tue 9/24, 10:30am
4 Tue 10/1, 10:30am
5 Tue 10/8, 10:30am
6 Tue 10/22, 10:30am
7 Tue 10/29, 10:30am

Test

The test is opportunity to synthesize concepts across weeks and solve new problems based on lessons learned. The test is open-book: you may use any and all non-human resources during the test, but the only humans to whom you may turn for help or from whom you may receive help are the course’s heads.

Release Deadline
Mon 11/4, 7:30pm Fri 11/8, 11:59pm

Tracks

The course’s final two weeks offer you a choice of lectures and problem sets:

  • web programming with HTML, CSS, and JavaScript (plus Python and SQL);
  • mobile app development for iOS with Swift or Android with Java; or
  • game development with Lua.

So that the tracks can happen in parallel, the lectures will be pre-recorded on video. You are encouraged, but not required, to select a track that might best prepare you for your choice of final projects.

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.

Milestone Date
Pre-Proposal Sun 11/10, 11:59pm
Proposal Sun 11/17, 11:59pm
Status Report Mon 12/2, 11:59pm
Implementation Sun 12/8, 11:59pm

October Recess

There will be no lecture, supersection, section, quiz, problem set, or office hours from Mon 10/14 through Sun 10/20.

CS50 Hackathon

From 7pm on Tue 12/3 until 7am on Wed 12/4 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 Mon 12/9 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.

Lateness

Late submissions (of quizzes, problem sets, the test, and the final project’s milestones) will be penalized at a rate of 0.1% per minute.

  • If you submit 10 minutes late, your score will be penalized 1%. Your score will thus be 99% of what it would have been if submitted on time.
  • If you submit 60 minutes late, your score will be penalized 6%. Your score will thus be 94% of what it would have been if submitted on time.
  • If you submit 1,000 minutes (just over 16 hours) late, your score will be penalized 100%. Your score will thus be effectively zeroed.

However, you may grant yourself one 3-day (72-hour) extension during the term for any one problem set. That extension cannot be apportioned among multiple problem sets or be applied to quizzes, the test, or the final project’s milestones. To grant yourself this extension, submit this form.

No exceptions to this policy will be considered unless requested of the course by your resident dean (or if you add the course late).

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 (and webcam, if not built-in) is helpful, particularly for office hours. Students without their own laptops (or with a laptop without webcam) 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 quizzes and test 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.

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.

Reasonable

  • 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.
  • Helping a classmate identify a bug in their code at office hours, elsewhere, or even online, as by viewing, compiling, or running their 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.
  • Submitting the same or similar work to this course that you have submitted previously to this course, CS50 AP, or CS50x.
  • Turning to the course’s heads for help or receiving help from the course’s heads during the quizzes or test.
  • 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 their 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 quizzes 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 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 quizzes or test.
  • 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 recordings@cs50.harvard.edu 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 recordings@cs50.harvard.edu.