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CS50 Course Overview

Jun 23, 2025

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Overview

This lecture series, CS50, is Harvard University’s Introduction to Computer Science, led by Dr. David Malan. The course covers foundational topics in computer science, programming, algorithms, and web development, aiming to teach students how to solve problems efficiently and understand the computational underpinnings of modern technology.

Course Structure & Goals

  • CS50 welcomes students with or without prior programming experience.
  • The focus is on problem-solving and expressing logic through code across a variety of fields.
  • Success in programming comes from starting early, practicing regularly, and breaking complex problems into manageable pieces.
  • The course promotes measuring your own progress ("delta") rather than comparing yourself to classmates.

Key Computer Science Concepts

  • Computational Thinking: Approach problems methodically, model solutions with clear inputs and outputs, and abstract out irrelevant details.
  • Information Representation: Computers use binary (base-2) to represent data; other systems include unary (base-1) and decimal (base-10).
  • Bits & Bytes: A bit is a single 0 or 1; eight bits make a byte, which represents values from 0 to 255.
  • Text Encoding: Text can be represented by ASCII (for English) and Unicode (for global languages and emoji); each character has a numeric code.
  • Other Data Representation: Colors are typically represented as RGB (red, green, blue); images and sound are quantized into numbers.
  • Abstraction: Simplifying problems by hiding unnecessary details, such as how a car engine works when you drive.
  • Algorithms: Clear, step-by-step instructions to solve a task. Example algorithms include linear search, binary search, and various sorting methods.

Programming Fundamentals

  • Programming Languages: Course begins with Scratch (a visual, block-based language) to illustrate computational concepts simply, followed by C (a low-level, text-based language), and then Python (a higher-level language).
  • Source Code & Machine Code: Programmers write code in languages like C or Python (source code), which is converted to machine code (binary) that computers execute.
  • Compilers: Tools that translate source code to machine code.
  • Programming Tools: Use Visual Studio Code (VS Code) in the cloud for coding; learn the command line for project and file management.
  • Core Constructs: Functions (group reusable code), variables (store values), conditionals (if/else logic), loops (repeat actions), and data types (int, float, string, char, etc.).

Problem Solving in Practice

  • Pseudo code: Writing logic in structured English to plan solutions before actual code.
  • Debugging: Systematic strategies for finding and fixing errors, including using print statements, debuggers, and talking through problems (rubber duck debugging).
  • Efficiency: Analyze algorithm performance with Big O notation, considering best and worst cases.
  • Project Examples: Creating interactive programs in Scratch (e.g., games), translating those concepts to C and Python, and later building web apps with HTML, CSS, JavaScript, and Python.

Web Development & Real-World Applications

  • Web Basics: Internet is a system of routers; data is sent in packets using protocols like TCP/IP.
  • Domain Name System (DNS): Converts human-readable web addresses to IP addresses.
  • HTTP/HTTPS: Web communication protocols; secure (https) uses encryption.
  • Web Technologies: Build web pages with HTML (structure), CSS (style), and JavaScript (interactivity).
  • Servers & Databases: Use Flask (Python framework) to build web apps and SQL to manage persistent data.
  • Sessions & Cookies: Used to store user data across web requests (e.g., shopping carts, logins).
  • APIs: Enable external data integration using formats like JSON.

Key Terms & Definitions

  • Bit — a binary digit, 0 or 1.
  • Byte — a group of 8 bits.
  • Binary — base-2 number system (used internally by computers).
  • ASCII — code for representing English letters/numbers as bytes.
  • Unicode — a universal character encoding for many world scripts and emojis.
  • Algorithm — a clear, finite set of instructions to solve a problem.
  • Function — reusable block of code performing a specific task.
  • Array/List — ordered sequence of values.
  • Big O Notation — describes how algorithms scale with input size.
  • Abstraction — simplifying complex systems by focusing on high-level operations.
  • HTTP Parameter — key-value pairs sent in web requests (e.g., ?q=search).
  • Cookie — data stored by a browser to maintain user state.
  • Session — server-side record to track user data across requests.

Action Items / Next Steps

  • Practice translating everyday problems into computational steps or algorithms.
  • Begin coding simple projects in Scratch, then progress to C and Python.
  • Explore debugging techniques—use print statements, VS Code’s debugger, or explain problems aloud.
  • Experiment with building and extracting information from web pages using HTML, CSS, JavaScript, and Flask.
  • For further skill-building, install developer tools (like VS Code) on your local machine.
  • Consider using password managers and two-factor authentication for your digital security.
  • Prepare for final projects and share your work at the CS50 fair.

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