Name: CS50 2018 - 回放3 - 記憶 (CS50 2018 - Lecture 3 - Memory)
Uploaded: 2021-01-14T07:57:06.000Z
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- That at 9:15, Ray Santoya was at the ATM.

- So the question is, what was he doing at 9:16?

- Shooting the nine-millimeter at something.

- And he's talking to whoever is wearing that jacket.

DAVID MALAN: This is he is CS50, and this is lecture 3, and that

And indeed, by the end of today, we'll make

clear exactly what's right, what's not right about that,

and hopefully give you some pause any time you watch TV or movies hereafter

and notice these little things that all too many writers seem

So recall that last time, we took a look lower level at what compiling actually

And recall that it was a few things, these four steps of pre-processing

and compiling and assembling and linking,

so that when you start with their source cod,

that might look like this code that we have written in the past,

you first have to preprocess it, and the first step in pre-processing was

converting all of those processor instructions--

anything starting with a hash at the beginning-- to their equivalents.

So opening the files and effectively copying and pasting the contents

there so that programs and the compiler know what get_string

The next step that came after that was actually

compiling, whereby compiling technically means taking that source

code, once it's been preprocessed, and printing and generating

this very cryptic-looking stuff called assembly code.

And those assembly codes or assembly instructions are really what the CPU--

the brain of your computer-- actually understands,

although technically the computer understands them only in the form

that assembly code, you actually get out those 0's and 1's.

But even that simplest of programs where we just prompt the user for a string

and then print out their name still involved a couple more files.

There was not only cs50.h and stdio.h at the top,

somewhere in the computer system there's probably files called cs50.c,

and in the case of stdio, printf.c, in which actually the code is

for those two functions, those two have to get compiled down

to 0's and 1's, and then we need to link everything together,

merging those 0's and 1's so that the computer has access to your code

and to printf's code and to the cs50 library's code And so forth.

But all of that we can just generally wrap up in the descriptor of compiling.

And so that's one of the looks we took last week.

And we also have introduced, last week and previously, a few tools.

And odds are, you're having as many frustrations perhaps already

with the p-sets as you are accomplishments

And that's normal, and rest assured that the scales will eventually tip more

toward happiness and away from sadness, but we'll

give you indeed more tools today than these for actually finding

help50, recall, helps you with what process?

When you instinctively consider using help50?

When you see error messages on the screen.

Something you don't understand that's the result of some mistake you

probably made but you don't quite understand what the computer is telling

you, run help50, and then that same command and we, the staff,

with our code will try to understand the message for you

It helps you see with red and green color coding exactly what spaces should

be there, shouldn't be there-- it just helps you pretty

your code so that you can read it better and other humans can as well.

And then printf, which is kind of like the coarsest tool in your tool box,

this is just helping you see not only messages you want to see,

You can print ints and strings, whatever you want,

and then you can delete those lines of printf

once you're confident your program's working.

But that gets a little tedious, and honestly, as our programs get bigger,

we're going to want more powerful tools than like manually printing things

out, recompiling, rerunning, it very quickly it gets tedious.

And the goal of programming is not to be tedious, but to be empowering,

and that's where we'll step to today via this.

So CS50 IDE is sort of fancier version of what

you've been using called CS50 Sandbox, and in turn, CS50 Lab.

Now recall that both of those tools, the Sandbox and the Lab,

have a terminal window where you can type commands,

they have a code editor where you can actually write your code,

and then they have a file browser with icons and such

where you can actually see your files and folders.

So it turns out that CS50 IDE is another tool that at first glance

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CS50 2018 - 回放3 - 記憶 (CS50 2018 - Lecture 3 - Memory)

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