Name: CS50 2017 - リーディング5 - データ構造 (CS50 2017 - Lecture 5 - Data Structures)
Uploaded: 2021-01-14T07:09:38.000Z
Duration: 1 h 45 min 40 s
Description: VoiceTubeの動画で発音を聞きながら英語表現を覚えよう！学べる英語：

And you'll recall perhaps that in this most current week,

you've probably been tackling a little something like this.

And if you don't actually have this experience from childhood,

what we're referring to in this problem set

is these kind of glasses that aren't 3-D glasses because it's both red eyes

or sometimes it's just a big piece of plastic.

But with this can you actually look up and see

And so this is the allusion to which we're referring

and the goal ultimately in problem set five's who done

it is to actually figure out how to implement that kind of red filter.

But to do that, you first have to understand

this thing, which at first glance, admittedly, looks pretty complicated.

But if you dived into the problem already,

you'll probably have wrapped your mind around at least

a few of these fields like the size of the image or the width of the image

and the height of the image, which should be a little more reasonably

But to implement this, you've had to deal with something

And so in C, we have this feature, recall.

And we didn't really play with this that much last time.

But you've seen it now in forensics, or you soon will.

And here we have the definition of a student.

So when C was invented decades ago, they didn't foresee

They had int and char and float and double.

But we can invent our own data types much like in Scratch.

We can make our own puzzle pieces as follows.

Typedef to define a type, struct to say here comes a structure.

And what is the structure known as student?

Well in this case, I arbitrarily decided that a student would just

have a name and a dorm and both of those would be strains.

And you can imagine putting other things in there

like ID numbers, phone numbers, email addresses, or whatnot

so that you can actually combine all of this information together.

So let's just take a quick look at how you might use code like this.

It's common, but not necessary to declare your structures inside

of a file that also starts with .h so that we can share it across multiple

programs just like with other libraries' header files.

And here I've taken those training wheels

off as before where, string is actually just a white lie for char star.

But this is really the same data structure

So let's take a quick look now at a program that actually uses

this in struct0.C. So let's take a look at what we've done here.

In struct0.C we have some header files up top.

But we also include this header file so that we have access

We first go ahead and ask the user for an integer called enrollment.

So hopefully they'll give us a positive number.

If we then do get back a number as expected in line 13,

How would you just describe what line 13 is doing at this point in the term?

DAVID MALAN: Yeah, give us an array of students of size enrollment.

So even though on line 11 and prior we didn't

know how many students we needed, we did get on line 12

And so on line 13 we declare an array using a variable saying,

give me this many elements, this many students in my array to store things.

And then we proceed, in the lines below, as follows.

We start iterating over the enrollment from zero on up to enrollment.

And we prompt the user on each iteration for a student's name and dorm.

And the right hand side of those two lines of code is pretty familiar.

But on the left hand side, we do have a slightly new piece of syntax.

We have students bracket I, which gives you the i-th students in the array.

But what piece of syntax perhaps jumps out at you?

Especially if you've never programmed before?

And we've not used this symbol just yet in this context.

So you can probably infer that .name and .dorm is somehow accessing

the student's name and the student's dorm.

And that's literally all that's happening.

This dot operator tells the computer, go inside of the student's structure

at that i-th location and store the string that's coming

So it's like taking a struct and then looking inside of it

and going very specifically to one of the elements therein.

We've never needed this .operator before because in the past, any array,

any variable we've had has just been a string or an int or float.

We haven't had anything to dive deeper into.

We've encapsulated, so to speak, inside of a student structure, name and dorm.

And then this last part is actually just a printing out

We're just printing out, so-and-so is in such-and-such a dorm

by passing in those two strings using our familiar percent S.

Now this program at the end of the day is kind of pointless

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CS50 2017 - リーディング5 - データ構造 (CS50 2017 - Lecture 5 - Data Structures)

literally

sort

bunch

constant