CS50 2017 Lecture 0

一个半月没在CSDN上写笔记了。
这一个半月也没学太多东西。
前半个月看完了（手抄一遍）Data Structure and Algorithms in Python 第一章，做完了课后习题。
后一个月看完了（手抄一遍）Data Structure and Algorithms in Python 第二章， 不会做课后习题。

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然后每天在家帮忙，干一些活。
旺季快过去了，也没我啥事儿了。赶紧多学些东西，早点儿找到工作。
再学习一遍这个CS50，复习一下以前学习的知识，找找学习的感觉。

官方笔记系统又全面：
Lecture 0 Notes

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Own experiences about the course.

Most people (68%) have never taken CS before.

Programming is solving problems

Binary

numbers
Transistors, which are tiny little switches that are on and off.
That is how we store informations.
We just need lots and lots of switches, certainly much smaller in order to represent information.

letters
mapping
ASCII, which is just an acronym describing a mapping from numbers to letters.
72 73 33 HI!

Unicode

Photos and videos
RGB
some Red, some Green, some Blue,

Byte, 8 bite.
3 Byte can represent any colors.

Abstraction

Permeates

Algorithms

step by step instructions for solving some problem.

Computational thinking, thinking like a computer.

implement how to make a sandwich.

Code

seach Mike in a phonebook

patterns
formalize the actions
pseudocode

pick up phone bookopen to middle of the booklook at namesif Smith is among names    call Mikeelse if Smith is earlier in the book    open to middle of left half of book    go back to step 2else if Smith is later in the book    open to middle of the right half of book    go back to step 2else    quit

Boolean expression is just a question with a yes or no answer, or True or False answer.

indent
loop
condition

Scratch

Via this language, we can distill that previous, more cryptic program into just a couple of puzzle pieces.

multi-threading, is a fancy way to saying a program can be written in such a way that it does two thing at once.

You got a gigaherz CPU or brain inside the computer or 2 gigahertz. Those number literally mean your Mac or PC can do a billion things in a second.

variable
loop
boolean expressions