Datasets:
pre-view
/
CS50-raw

Dataset card Data Studio Files
xet
 Community
1
text
stringlengths
1
81
start
float64
0
10.1k
duration
float64
0
24.9
>> And, indeed, any time you feel yourself copying and pasting,
6,912.57
2.5
and not even changing code, odds are there's a better way.
6,915.07
2.63
And, indeed, there is.
6,917.7
1.77
Let me go ahead and do a for loop, even though the syntax might not
6,919.47
3.04
come naturally yet.
6,922.51
2.06
>> Do this three times, simply by doing the following--
6,924.57
4.924
and I happen to know this from practice.
6,929.494
1.666
But we have a number of examples now.
6,931.16
1.65
And you'll see online more references still.
6,932.81
2.14
>> This is the syntax on line 6, that much like Scratch that repeats
6,934.95
2.84
block, repeat the following three times.
6,937.79
2.3
It's a little magical for now.
6,940.09
1.25
But this will get more, and more familiar.
6,941.34
1.71
>> And it's going to repeat line eight three times,
6,943.05
2
so that if I re-compile make cough, dot slash cough, cough, cough, cough.
6,945.05
7.34
It still works the same way.
6,952.39
1.64
So that's all fine and good.
6,954.03
1.52
But that's not very abstracted.
6,955.55
2.65
>> It's perfectly correct.
6,958.2
1.171
But it feels like there could be an opportunity,
6,959.371
1.999
as in the world of Scratch, to kind of start
6,961.37
2.38
to add some semantics here so that I don't just have some for loop,
6,963.75
3.78
and a function that says cough, or does cough.
6,967.53
2.337
You know what?
6,969.867
0.583
Let me try to be a little cooler than that,
6,970.45
2.17
and actually write a function that has some side effects, call it cough.
6,972.62
3.47
>> And it takes no input, and returns no value as output.
6,976.09
4.74
But you know what it does?
6,980.83
1.85
It does this-- printf, quote unquote, cough.
6,982.68
6.69
>> And now up here, I'm going to go ahead and for int,
6,989.37
3.01
i gets zero, i less than 3, i plus plus.
6,992.38
3.69
I'm going to not do printf, which is arguably a low level implementation
6,996.07
3.7
detail.
6,999.77
0.5
I don't care how to cough.
7,000.27
1.083
I just want to use the cough function.
7,001.353
1.887
And I'm just going to call cough.
7,003.24
1.6
>> Now, notice the dichotomy.
7,004.84
1.364
When you call a function, if you don't want to give it inputs, totally fine.
7,006.204
3.166
Just do open paren, close paren, and you're done.
7,009.37
2.41
>> When you define a function, or declare a function's prototype,
7,011.78
4.491
if you know in advance it's not going to take any arguments,
7,016.271
2.499
say void in those parentheses there.
7,018.77
2.4
And that makes certain that you won't accidentally misuse it.
7,021.17
4.49
Let me go ahead and make cough.
7,025.66
1.36
And, of course, I've made a mistake.
7,027.02
1.52
>> Dammit, there's that implicit declaration.
7,028.54
1.87
But that's fine.
7,030.41
0.915
It's an easy fix.
7,031.325
1.265
I just need the prototype higher up in my file than I'm actually using it.
7,032.59
5.65
>> So now let me make cough again, nice.
7,038.24
1.83
Now, it works.
7,040.07
0.72
Make cough, cough, cough, cough.
7,040.79
2.14
So you might think that we're really just over engineering this problem.
7,042.93
3
And, indeed, we are.
7,045.93
0.833
This is not a good candidate of a program
7,046.763
2.107
at the moment for refactoring, and doing what's
7,048.87
3.06
called hierarchical decomposition, where you take some code, and then
7,051.93
3.715
you kind of factor things out, so as to ascribe more semantics to them,
7,055.645
3.145
and reuse it ultimately longer term.
7,058.79
2.14
But it's a building block toward more sophisticated programs
7,060.93
2.56
that we will start writing before long that
7,063.49
2.11
allows us to have the vocabulary with which to write better code.
7,065.6
4.49
And, indeed, let's see if we can't generalize this further.
7,070.09
2.83
>> It seems a little lame that I, main, need to worry about this darn for loop,
7,072.92
5.064
and calling cough again and again.
7,077.984
1.416
Why can't I just tell cough, please cough three times?
7,079.4
3.65
In other words, why can't I just give input to cough and do this?
7,083.05
5.12
>> Why can't I just say, in main cough three times.
7,088.17
3.1
And now, this is kind of magical.
7,091.27
1.88
It's very iterative here.
7,093.15
1.39
And it's, indeed, a baby step.
7,094.54
1.4
>> But just the ability to say on line eight, cough three times,
7,095.94
3.31
it's just so much more readable.
7,099.25
1.48
And, plus, I don't have to know or care how cough is implemented.
7,100.73
3.48
And, indeed, later in the term and for final projects,
7,104.21
2.25
if you tackle a project with a classmate or two classmates,
7,106.46
2.69
you'll realize that you're going to have to, or want to, divide the work.
7,109.15
3.22
>> And you're going to want to decide in advance, who's going to do what,
7,112.37
2.28
and in which pieces?
7,114.65
0.833
And wouldn't it be nice if you, for instance,
7,115.483
2.037
take charge of writing main, done.
7,117.52
2.58
And your roommate, or your partner more generally,
7,120.1
3.37
takes care of implementing cough.
7,123.47
1.76
>> And this division, these walls of abstraction,
7,125.23
4.31
or layers of abstraction if you will, are super powerful,
7,129.54
2.77
because especially for larger, more complex programs and systems,
7,132.31
3.17
it allows multiple people to build things together, and ultimately
7,135.48
4.59
stitch their work together in this way.
7,140.07
2.61
But, of course, we need to now fix cough.
7,142.68
2.652
We need to tell cough that, hey, you know what?
7,145.332
1.958
You're going to need to take an input-- so not void, but int and now.
7,147.29
3.94
Let's go ahead and put into cough the int. i gets zero.
7,151.23
3.94
>> i is less than how many times.
7,155.17
1.72
I said three before.
7,156.89
1.66
But that's not what I want.
7,158.55
1.87
I want cough to be generalized to support any number of iterations.
7,160.42
5.1
>> So, indeed, it's n that I want, whatever the user tells me.
7,165.52
3.28
Now, I can go ahead and say print cough.
7,168.8
2.82
And no matter what number the user passes in,
7,171.62
3.13
I will iterate that many times.
7,174.75
2.14