CS50 Lecture Notes

Introduction to CS50

• Presented by David J. Malan
• Harvard University's introduction to computer science and programming.
• Conducted in Loeb Drama Center instead of Sanders Theater.
• Collaboration with American Repertory Theater, new space, and amenities.

Historical Context

• A watercolor painting from 1794 by Jonathan Fisher representing early Harvard buildings is showcased.

Personal Experience

• David shares his experience of taking CS50 20 years ago.
• Initial trepidation about studying computer science.
• Emphasis on problem-solving rather than just programming.
• Approximately two-thirds of students have no prior computer science experience.
• Focus on individual progress rather than competitive comparison.

Course Structure

• Initial programming assignment: recreating a portion of Super Mario Brothers using ASCII art.
• Later programming assignments include creating "CS50 Finance," a web application for stock trading.
• Capstone experience: final project.

What is Computer Science?

• Definition of computer science as problem solving:
  • Input (the problem) ➔ Processing (black box of code) ➔ Output (solution).
• Importance of a common language for representing inputs and outputs.

Representation of Information

Unary Notation

• Old school style of counting with fingers, referred to as unary notation.

Decimal System

• Base 10 system (0-9) commonly used by humans.

Binary System

• Computers use binary (base 2), only 0s and 1s.
• Bits: Binary digits, the fundamental units of data in computing.

Representation of Higher Numbers

• Explanation of counting with light bulbs as a metaphor for binary counting.
• Counting using 3 light bulbs allows representation of numbers from 0 to 7.

Transistors and Computation

• Computers utilize millions of transistors (tiny switches) to represent 0s and 1s.

ASCII and Character Representation

• ASCII (American Standard Code for Information Interchange) maps numbers to letters and symbols.
• Example: The letter "A" corresponds to 65 in decimal and its binary representation.
• Explanation of communication in computers using ASCII.

Color Representation in Computers

RGB Model

• Colors represented through additive mixing of red, green, and blue light.
• 24 bits used to represent colors in images (8 bits for each color).

Video and Music Representation

• Video as a sequence of images displayed rapidly; sound can be represented by notes and durations.

Algorithms

• Definition: Step-by-step instructions for problem-solving.
• Importance of precision in programming for computers.
• Example: Searching for a name in a phone book through different algorithms (linear vs. binary search).

Programming Constructs

Functions

• Actions or verbs in programming that perform specific tasks.

Conditions and Loops

• Decision-making processes (if statements) and repetition (for loops).

Scratch Programming

• Introduction to Scratch as a user-friendly graphical programming language.
• Example of simple programs: Hello World, asking for user input.
• Use of variables to store information and enable dynamic responses.

Creating More Complex Programs

• Demonstration of creating interactive programs with multiple sprites and events.
• Use of sound and motion to enhance user interaction.

Conclusion

• Emphasis on building upon simple ideas to create complex systems in programming.
• Encouragement to explore and develop skills in computer science and programming.