This is CS50x - Introduction to Computer Science
Goal - to get a better understanding of the fundermentals of programming.
Week 0 Scratch
Assignment
- 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.
- Loops are under control and include
foreverrepeatandrepeat until
- Loops are under control and include
- 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.
Computer science is fundamentally about problem solving with computers.
We can think of problem solving as the process of taking an input and getting to the output (the solution to our problem).
flowchart LR
input -->box[a box ]
box -->output
How do you get from zeros 000 to the objects moving on the screen of a phone. Since computers run on electricity which can be turned off, then on we just represent a bit by turning some switch on and off again to represent 0 or 1 that computers understand. Modern computers have billions of switches called transistors that can be turned off and on to represent different values.
000 = 0 001 = 1 010 = 2 011 = 3 100 = 4 …. 111 = 7
Representing numbers in binary!
To count people in a room we may use our fingers in a system call unary, where each digit represents a single value of one.
To count higher we might need to use ten digits, 0 through to 9, with a system called decimal.
Computers use a simpler system called binary with just two digits 0 and 1.
| 4 | 2 | 1 | ||
|---|---|---|---|---|
| 0 | 0 | 0 | = | 0 |
| 0 | 0 | 1 | = | 1 |
| 0 | 1 | 0 | = | 2 |
| 0 | 1 | 1 | = | 3 |
| 1 | 0 | 0 | = | 4 |
| 1 | 0 | 1 | = | 5 |
| 1 | 0 | 1 | = | 6 |
| 🔥 | 🔥 | 🔥 | = | 🔥7🔥 |
Each binary digit is also called a bit To count higher than 7 you need to add another bit Most computers use 8 bits at a time, like 00000011 for the number 3.
And the pattern to count in binary with multiple bits is the same as the pattern in decimal with multiple digits.
For example, we know the following number in decimal represents one hundred and twenty-three. 1 2 3
The 3 is in the ones place, the 2 is in the tens place, and the 1 is in the hundreds place. So 123 is 100×1 + 10×2 + 1×3 = 100 + 20 + 3 = 123.
Each place for a digit represents a power of ten, since there are ten possible digits for each place. The rightmost place is for 100, the middle one 101, and the leftmost place 102:
| \(10^2\) | \(10^1\) | \(10^0\) |
|---|---|---|
| 1 | 2 | 3 |
Text
ASCI the or American Standard Code for Information Interchange is a chart to map characters to letters
When we receive a text message, we might be getting patterns of bits that have the decimal values 72, 73, and 33. Those bits would map to the letters HI!. And the sequences of bits we receive would look like 01001000, 01001001, and 00100001, with 8 bits for each character.
| 72 | 73 | 33 |
| H | I | ! |
With eight bits, or one byte, we can have 28, or 256 different values (including zero). (The highest value we can count up to would be 255.)
A Byte = 8 Bits
Unicode allows for Emoji's 🥳
For example, the “face with medical mask” emoji is just the four bytes 11110000 10011111 10011000 10110111
This is then interpreted by your operating system hence the differences between iOS and Android
Colours and images, video and sound
| R | G | B |
| 72 | 73 | 74 |
Each number might be 8 bits, with 256 possible values, so with three bytes, or 24 bits, we can represent millions of colors. Our three bytes from above would represent a dark shade of yellow:
The dots, or squares, on our screens are called pixels, and images are made up of many thousands or millions of those pixels as well. So by using three bytes to represent the color for each pixel, we can create images. We can see pixels in an emoji if we zoom in.
Videos are sequences of many images, changing multiple times a second to give us the appearance of motion, as a flipbook might.
Music can be represented as bits also, MIDI Musical Instrument Digital Interface which represents music with numbers for each of the notes and their duration and volume.
All of these ideas are just zeroes and ones interpreted and used by your computers software.
- There are other formats, some of which use compression (mathematical ways to represent some data with fewer bits), or some which might be containers that store multiple types of data together.
- And since there are many companies and groups developing software, we have lots of different file formats in existence, each with their own ways of representing data. But there are also organizations that work on some consensus, like the one responsible for maintaining the Unicode standard.
Algorithms
Lecture 1 - C
Hello, World 🌏
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#include <stdio.h>
int main (void)
{
printf ("hello, world");
}
headers and libraries
Including
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#include <stdio.h>
types
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bool
char
double
float
int
long
string
format codes
Getting
%c char
operators
+, - %
variables and syntactic sugar
variables go right to left int counter = 0;
counter++;