Name: 2016年CS50--第2周--數組 (CS50 2016 - Week 2 - Arrays)
Uploaded: 2021-01-14T06:50:46.000Z
Duration: 1 h 50 min 54 s
Description: 【看影片學英語】數萬部 YouTube 影片，搭配英漢字典即點即查，輕鬆掌握單字發音與用法，長久累積看電影不必再看字幕。

This is CS50 and this is the start of Week 2.

And you'll recall that over the past couple of weeks,

we've been introducing computer science and, in turn, programming.

>> And we started the story by way of Scratch, that graphical language

And then most recently, last week, did we

introduce a higher-- a lower-level language known

And, indeed, last time we explored within that context

>> This, recall, was the very first program we looked at.

And this program, quite simply, prints out, "hello, world."

But there's so much seeming magic going on.

There's this #include  with these angle brackets.

There's parentheses, curly braces, semi-colons, and so much more.

>> And so, recall that we introduced Scratch

so that we could, ideally, see past that syntax, the stuff that's really not

all that intellectually interesting but early on

is, absolutely, a bit tricky to wrap your mind around.

And, indeed, one of the most common things early on in a programming class,

especially for those less comfortable, is to get frustrated by

and tripped up by certain syntactic errors, not to mention logical errors.

And so among our goals today, actually, will

be to equip you with some problem-solving techniques for how

to better solve problems themselves in the form of debugging.

And you'll recall, too, that the environment that we introduced

This is web-based software that allows you to program in the cloud,

so to speak, while keeping all of your files together, as we again will today.

And recall that we revisited these topics here,

among them functions, and loops, and variables, and Boolean expressions,

And actually a few more that we translated from the world of Scratch

>> But the fundamental building blocks, so to speak,

In fact, we really just had a different puzzle piece, if you will.

Instead of that purple save block, we instead

had printf, which is this function in C that

allows you to print something and format it on the screen.

We introduced the CS50 Library, where you

have now at your disposal get_char, and get_int, and get_string,

and a few other functions as well, via which you can get input

And we also took a look at things like these- bool, and char,

and double, float, int, long_long string.

>> In other words, when you declare a variable to store some value,

or when you implement a function that returns some value,

you can specify what type of value that is.

Is it a string, like a sequence of characters?

Is it a floating point value, or the like?

So in C, unlike Scratch, we actually began to specify what kind of data

>> But, of course, we also ran into some fundamental limits of computing.

And in particular, this language C, recall

that we took a look at integer overflow, the reality

that if you only have a finite amount of memory

or, specifically, a finite number of bits, you can only count so high.

And so we looked at this example here whereby a counter in an airplane, ,

actually, if running long enough would overflow and result in a software

>> We also looked at floating point imprecision, the reality

that with only a finite number of bits, whether it's 32 or 64,

you can only specify so many numbers after a decimal point, after which you

So for instance, one-third in the world here, in our human world,

we know is just an infinite number of 3s after the decimal point.

But a computer can't necessarily represent an infinite number of numbers

if you only allow it some finite amount of information.

>> So not only did we equip you with greater power in terms

of how you might express yourself at a keyboard in terms of programming,

we also limited what you can actually do.

And indeed, bugs and mistakes can arise from those kinds of issues.

And indeed, among the topics today are going to be topics like debugging

and actually looking underneath the hood at how things were introduced last week

are actually implemented so that you better

understand both the capabilities of and the limitations of a language like C.

>> And in fact, we'll peel back the layers of the simplest of data structure,

something called an array, which Scratch happens to call a "list."

It's a little bit different in that context.

And then we'll also introduce one of the first of our domain-specific problems

in CS50, the world of cryptography, the art of scrambling

or in ciphering information so that you can send secret messages

and decode secret messages between two persons, A and B.

>> So before we transition to that new world,

let's try to equip you with some techniques with which you can eliminate

or reduce at least some of the frustrations

that you have probably encountered over the past week alone.

In fact, ahead of you are such-- some of your first problems in C. And odds are,

if you're like me, the first time you try to type out a program,

even if you think logically the program is pretty simple,

you might very well hit a wall, and the compiler is not going to cooperate.

Make or Clang is not going to actually do your bidding.

字幕列表影片播放

2016年CS50--第2周--數組 (CS50 2016 - Week 2 - Arrays)

figure

character

realize

negative