text stringlengths 1 81 | start float64 0 10.1k | duration float64 0 24.9 |
|---|---|---|
>> And why was that? | 1,205.99 | 1.17 |
What was the code that we wrote before
that ensured that the cursor would | 1,207.16 | 5.24 |
go on the next line? | 1,212.4 | 2.482 |
Funny thing about a
computer is it's only going | 1,214.882 | 1.958 |
to do literally what you tell it to do. | 1,216.84 | 1.73 |
>> So if you tell it to printf hello,
comma, space, world, close quote, | 1,218.57 | 7.48 |
it's literally only going
to print those characters. | 1,226.05 | 3.04 |
But I had this special character
at the end, recall, backslash n. | 1,229.09 | 2.89 |
And that's what ensured
that the character went | 1,231.98 | 2.25 |
to the next line of the screen. | 1,234.23 | 2.34 |
>> In fact, let me go and do this. | 1,236.57 | 1.527 |
Let me go ahead and delete this. | 1,238.097 | 1.333 |
Now, notice that the
top of my screen there's | 1,239.43 | 1.75 |
a little red light in
the tab indicating, | 1,241.18 | 1.71 |
hey, you've not saved your file. | 1,242.89 | 2.157 |
So I'm going to go ahead with control
S or command S, save the file. | 1,245.047 | 2.833 |
Now it goes-- went for a moment-- green. | 1,247.88 | 3.25 |
And now it's back to
just being a close icon. | 1,251.13 | 2.63 |
>> If I now run clanghello.c again,
Enter, dot slash, a.out, Enter, | 1,253.76 | 8.1 |
you'll see that it still worked. | 1,261.86 | 2.25 |
But it's arguably a little buggy. | 1,264.11 | 1.91 |
Right now, my prompt-- workspace,
and then that dollar sign, | 1,266.02 | 2.694 |
and then my actual prompt--
is all on the same line. | 1,268.714 | 2.166 |
So this certainly an aesthetic bug,
even if it's not really a logical bug. | 1,270.88 | 3.66 |
>> So I'm going to undo what I just did. | 1,274.54 | 1.71 |
I'm going to rerun a.out. | 1,276.25 | 2.31 |
Notice I've added the
newline character back. | 1,278.56 | 4.15 |
I've saved the file. | 1,282.71 | 1.57 |
>> So I'm going to rerun a.out, and--
dammit, a bug, a bug meaning mistake. | 1,284.28 | 7.35 |
So the bug is that even though
I added the backslash n there, | 1,291.63 | 3.39 |
re-saved, re-ran the program,
the behavior was the same. | 1,295.02 | 6.16 |
Why would that be? | 1,301.18 | 1.46 |
>> I'm missing a step, right? | 1,302.64 | 1.27 |
That key step earlier was that you have
to-- when you change your source code, | 1,303.91 | 3.71 |
it turns out also run
it through the compiler | 1,307.62 | 1.99 |
again so you get new machine code. | 1,309.61 | 1.492 |
And the machine code,
the zeros and ones, | 1,311.102 | 1.708 |
are going to be almost identical, but
not perfectly so, because we need, | 1,312.81 | 3.45 |
of course, that new line. | 1,316.26 | 1.25 |
>> So to fix this, I'm going to need
to rerun clanghello.c, enter, dot | 1,317.51 | 5.13 |
slash, a.out. | 1,322.64 | 1.16 |
And now, hello world is back
to where I expect it to be. | 1,323.8 | 4.602 |
So this is all fine and good. | 1,328.402 | 1.208 |
But a.out is a pretty stupid name for a
program, even though it happens to be, | 1,329.61 | 3.54 |
for historical reasons, the
default-- meaning assembly outputs. | 1,333.15 | 3.38 |
>> But let me go ahead here
and do this differently. | 1,336.53 | 4.25 |
I want my hello world program
to actually be called hello. | 1,340.78 | 3.98 |
So if it were an icon on my
desktop, it wouldn't be a.out. | 1,344.76 | 3.56 |
It would be called hello. | 1,348.32 | 1.41 |
>> So to do this, it turns out
that Clang, like many programs, | 1,349.73 | 3.93 |
supports command line arguments,
or flags, or switches, | 1,353.66 | 4.32 |
which simply influence its behavior. | 1,357.98 | 1.62 |
Specifically, Clang supports a dash o
flag, which then takes a second word. | 1,359.6 | 5.56 |
In this case, I'll arbitrarily,
but reasonably, call it hello. | 1,365.16 | 3.03 |
But I could call it anything
I want, except a.out, which | 1,368.19 | 2.52 |
would be rather besides the point. | 1,370.71 | 1.68 |
>> And then just specify the name
of the file I do want to compile. | 1,372.39 | 3.25 |
So now even though at the beginning
of the command I still have Clang, | 1,375.64 | 3.55 |
at the end of the command
I still have the filename, | 1,379.19 | 2.22 |
I now have these command line
arguments, these flags that are saying, | 1,381.41 | 4.11 |
oh, by the way, output-o, a file
called hello, not the default a.out. | 1,385.52 | 5.66 |
>> So if I hit Enter now, nothing
seems to have happened. | 1,391.18 | 2.63 |
And, yet, now I can do dot slash hello. | 1,393.81 | 4.09 |
So it's the same program. | 1,397.9 | 1.189 |
The zeros and ones are
identical at the end of the day. | 1,399.089 | 2.291 |
>> But they're in two
different files-- a.out, | 1,401.38 | 2.83 |
which is the first version
and just foolishly named, | 1,404.21 | 2.28 |
and now hello, which is a much
more compelling name for a program. | 1,406.49 | 3.76 |
But, honestly, I am never
going to remember this again, | 1,410.25 | 2.945 |
and again, and again. | 1,413.195 | 0.875 |
And, actually, as we write
more complicated programs, | 1,414.07 | 2.341 |
the commands you're
going to have to write | 1,416.411 | 1.749 |
are going to get even
more complicated still. | 1,418.16 | 2.76 |
>> And so not to worry. | 1,420.92 | 1.02 |
It turns out that humans before
us have realized they too | 1,421.94 | 4.28 |
had this exact same problem. | 1,426.22 | 1.31 |
They too did not enjoy having to
type fairly long, arcane commands, | 1,427.53 | 3.37 |
let alone remember them. | 1,430.9 | 1.3 |
And so humans before us have made
other programs that make it easier | 1,432.2 | 3.87 |
to compile your software. | 1,436.07 | 1.6 |
>> And, indeed, one such
program is called Make. | 1,437.67 | 3.939 |
So I'm going to go ahead and do this. | 1,441.609 | 1.541 |
I'm going to undo everything I
just did in the following way. | 1,443.15 | 2.541 |
Let me type LS. | 1,445.691 | 1.999 |
And you'll notice three things--
a.out, and a star, hello | 1,447.69 | 3.29 |
and a star, and hello.c. | 1,450.98 | 1.83 |
Hopefully, this should
be a little intuitive, | 1,452.81 | 1.92 |
insofar as earlier there was
nothing in this workspace. | 1,454.73 | 3.49 |
There was nothing that I had
created until we started class. | 1,458.22 | 3.02 |
>> And I created hello.c. | 1,461.24 | 1.6 |
I then compiled it, and called it a.out. | 1,462.84 | 1.704 |
And then I compiled it again slightly
differently and called it hello. | 1,464.544 | 2.916 |
So I have three files in this directory,
in this folder called Workspace. | 1,467.46 | 5.37 |
Now, I can see that as well
if I zoom out actually. | 1,472.83 | 2.175 |
>> If I zoom out here and
look at that top right hand | 1,475.005 | 2.525 |
corner, as promised the left
hand side of your screen | 1,477.53 | 2.41 |
is always going to show you
what's in your account, what's | 1,479.94 | 3.05 |
inside of CS50 IDE. | 1,482.99 | 1.8 |
And there is three files there. | 1,484.79 | 1.89 |
>> So I want to get rid of a.out and hello. | 1,486.68 | 2.39 |
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