Week 0 Scratch⚓︎

Syllabus⚓︎

Computer Science. Computational Thinking. Problem Solving: Inputs, Outputs. Representation: Unary, Binary, Decimal, ASCII, Unicode, RGB. Abstraction. Algorithms. Running Times. Pseudocode. Scratch: Functions, Arguments, Return Values; Variables; Boolean Expressions, Conditionals; Loops; Events; Threads.

Notes⚓︎

Binary⚓︎

Computer is a base-2 system we can use 0 and 1 to represent all of it.

Case: Use a hand to count by moving the fingers up and down. How high can you count?

The answer is 31 if you start with 0 (we have \(2^{5}\) outcomes).

bit⚓︎

For the computer, it is useful and simple because it imply the on and off.

binary digit-BIT!

We can make the value 1 mean on and 0 mean off, and use light bulbs to represent the fingers being up and down.

decimal⚓︎

\(123=100*1+10*2+1*3\)

And we can use this method to understand the bulbs' light, and going further brings us to binary. We can use 0 and 1 to represent information in a computer.

More often used than a bit is a byte. What is a byte? A byte is 8 bits (or 8 bulbs); it can represent 255.

ASCII⚓︎

So how can we use them to denote the letter A? Assign every letter a number—for some reason, A starts with 65 (64+1).

Unicode⚓︎

Unicode code point U+1F602

Remark: The U+ is a conventional mark for Unicode in computer science.

Color⚓︎

Zeros and ones can be used to represent color.

Red, green, and blue (called RGB) are a combination of three numbers.

One pixel dot will occupy 3 bits of color.

We will think about more things that can be represented by 0's and 1's, so what is between the input and output?

It's algorithms!

Algorithms⚓︎

Case: Find John Harvard in the book and take three algorithms.

one step each
two steps each
half of the remaining entries

We can solve the problem correctly and more efficiently as well.

A graph can show the efficiency.

Text Only

Pick up phone book
Open to middle of phone book
look at page 
If person is on page
    call him
Else if person is ealier in book
    Open to middle of left half of book
    Go back to line 3
Else if person is later in book
    Open to middle of right half of book
    Go back to line 3
Else
    Quit

They are called functions and use conditions.

Boolean expressions can give two types of answers (0 and 1 or something else).

And above, there is a loop that can go on and on.

Artificial Intelligence⚓︎

If we use simple binary questions as input, each with an answer, it will be difficult.

Large language models (LLMs)

C

#include<stdio.h>

int main(void)
{
    printf("hello world\n")
}

Scratch⚓︎

Drag and drop some puzzle pieces to make a program.

Very interesting parts.

Ivy's Hardest Game—so difficult! (Can it be passed?)

Summing up⚓︎

In this lesson, you learned how this course sits in the wide world of computer science and programming. You learned…

Few students come to this class with prior programming experience!
You are not alone! You are part of a community.
Problem-solving is the essence of the work of computer scientists.
This course is not simply about programming – this course will introduce you to a new way of learning that you can apply to almost every area of life.
How numbers, text, images, music, and video are understood and represented by computers.
The fundamental programming skill of pseudocoding.
Reasonable and unreasonable ways to utilize AI in this course.
How abstraction will play a role in your future work in this course.
The basic building blocks of programming including functions, conditionals, loops, and variables.
How to build a project in Scratch.

This was CS50! Welcome aboard! See you next time!

Problem Set 0⚓︎

It’s time to choose your own adventure! Your assignment, quite simply, is to implement in Scratch, at scratch.mit.edu, any project of your choice, be it an interactive story, game, animation, or anything else, subject only to the following requirements:

Your project must use at least two sprites, at least one of which must not be 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 conditional, at least one loop, and at least one variable.
Your project must use at least one custom block that you have made yourself (via Make a Block), which must take at least one input.
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 Ivy’s Hardest Game.

Due to Scratch's high degree of freedom, I pass the problem set (or make an easy one?).