Name: CS50 VR 2019 - 講義0 - 計算思考、スクラッチ (CS50 VR 2019 - Lecture 0 - Computational Thinking, Scratch)
Uploaded: 2021-01-14T10:24:07.000Z
Duration: 1 h 2 min 26 s
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This is CS 50 Harvard University's introduction to the Intellectual Enterprises of Computer Science and the Arts of Programming.

動名詞

Ah, my name is David Malin, and I actually took this course myself sophomore year some years ago, but but I almost didn't At the time, I was quite uneasy with the idea, frankly, of taking a computer science course, let alone this course.

過去形

And so my freshman year, at least, I really gravitated towards courses and departments with which I was much more familiar.

Computer science was well beyond my comfort zone at the time, and it was really these unfamiliar waters that I wasn't quite ready to shop even my first year.

But sophomore year, I finally got up the nerve to come, like through the door of CS 50 and on Lee, because the professor at the time let me take the course pass fail.

I was that uneasy, and if only I had known at the time what I now know, which is.

The 2/3 of CS 50 students have never taken a computer science course before, so if you are feeling similarly uneasy with the idea of trying something new, or even if you have prior background but are looking to fill in gaps in your knowledge.

If you're particularly self taught, realize you are very much in good company.

And ultimately, what matters in this course is not so much where you end up relative to your classmates, but where you end up relative to yourself when you began.

So what, then, is computer science and what was it that I was so uneasy with?

Well, I dare say we can describe computer science is this?

It's just the process of solving problems and what does it mean to solve a problem?

You've got some input, and the goal is to get some output.

The solution to that particular problem and in between really is computer science, and we'll see what's in this literal black box on the screen as we begin to fill in some of those blanks.

But when we consider ah problem to be solved, we have to all agree from the gecko, especially for using machines.

How are we going to represent these inputs and outputs?

And so one of the first concept we explore in computer science is how you represent information itself and odds are, you probably know, coming into this course that's computers only Speak what language.

Aaron, if you've never heard that term before, Fine as well, But zeros in one somehow.

Well, even if you kind of know the computer, speak binary, whatever that means.

But you haven't necessarily thought about how that works.

Will consider how most of us learn Tout accounts.

If I want to count the number of people in the room, I might do 12345 putting up one finger for every person in the room.

So that's what's known as you Neri notation you are, you know, implying one, because I'm just putting up a finger or not to count people in the room.

Of course, I can only count so high on just one hand, but thankfully, we have many symbols in our so called human world of decimal dec, meaning 10.

We have digits zero through nine, and from there we can express any numbers with which we're all familiar.

But computers don't have that many digits.

And yet somehow they're able to store not only numbers, but letters and images and videos and sounds, and so much more.

Well, let's take a quick look at just this to get everyone on the same page as to how you can build the phones in our pockets.

The laptops on our desk today using just zeros and ones.

Well, this are just symbols on the screen here.

I mean, these literally are just symbols, or GL ifs on the screen, sort of strokes of a pen that we all ascribe meaning to.

Well, if you're like me, you probably learned way back when to think of the right most digit as being in the ones place with one's Call them.

The middle digit is being in the tens place, and the left most digit is being in the hundreds place.

So how do we get from this pattern of 1 to 3 to the number 123?

Well, it's, um, quick mental math that we all just do instinctively.

It's 100 times one plus two times, 10 times two plus one times three.

That, of course, gives us 100 plus 20 plus three or 123.

So all of us just kind of take that process for granted now.

But it turns out that there's a system at play here, a system such that we can figure out any number in the same way.

So if we've got our one's place tens place in hundreds place, of course, in the decimal world, this is the number one.

This is the number 23456789 Something interesting happens, Of course.

Or if we ignore the leading zeros as being insignificant?

Well, just cause it's 10 times one plus one time zero.

So that's the system we've been using for years, and it turns out that these columns realize are just powers of 10.

So 10 to the zero is one tend to the one is 10 and tend to the two is 100.

And that's how we got ones tens and hundreds.

Now, in the computer world, you don't have 10 digits.

So we can just make a little tweak to our mental model here, so to speak.

And just now, use two powers of two instead of powers of 10.

So that means the right hand column is gonna be one.

The middle column is gonna be to the left column is gonna be four.

And if we kept going, it be 8 16 32 instead of 1000 10,000, 100,000.

So I propose that computers on Lee speak zeros and ones, of course.

But how do they represent larger numbers than zero and one?

What pattern of symbols on the screen would represent the number we humans know is too.

So even if you just generally knew what buying that binder is spoken by computers, it just means that a computer to represent the number we know is to somehow stores a pattern of symbols of 010 How do they represent three 011 for the same reason?

It's two times one plus one times one gives us, of course, three.

And now, just as before when we went 9 to 10.

Now we actually go from 3 to 4 by carrying the one now.

So in binary by meaning to hence, the zero and 1100 is not 100 per se.

It is literally the number we know it's for, and we can keep going on up.

And what happens if we want to represent eight s?

So we kind of have to solve this somehow.

We need another digit, and that's fine, right?

In math class, you would just add another place, another column in order to get back the value that you want.

So we need more zeroes or ones otherwise now known as bit.

If you've ever heard of the phrase bit, it just means binary digit and a zero or a one.

It's just something we know is a bit And why is this remain to computers?

Well, it's fancy is our Macs and PCs and phones are today.

After all that, at the end of the day, what do you have to do typically with your your laptop, your desktop, your phone these days?

What do you do with the very end of the day s So you charge it right, you plug it into some physical resource.

That is the Onley physical resource into these computers that we use today.

And that's kind of nice, because, of course, the court can either be plugged in or not plugged in.

Or maybe we could call that a one or a zero, True or false, on or off.

Which is to say, if electricity is our only input and there's either yes, electricity or no electricity will.

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CS50 VR 2019 - 講義0 - 計算思考、スクラッチ (CS50 VR 2019 - Lecture 0 - Computational Thinking, Scratch)

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