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OK, so now it is time for us to really pick apart that Hello World program and kind of analyze it so

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we can really see what every line is actually doing other than me just giving that basic explanation

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of each line.

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We haven't really learned about what all this stuff means, and although there's a lot going on there,

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I think that it is simple enough for us to cover it in one lecture here.

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So let's take a deep dive into this Hello world program.

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So we're going to start from top to bottom, and I'm going to give the best explanation I can of each

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line in the program.

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So first off, we start out with that include thing, right?

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It's a hashtag and then the word include.

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And then there's a space, and then it says, I'll stream in between less than and greater, then sign.

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So the include is something called the include directive.

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And all this means is that it says go search for another file that has code in it.

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And put the code that is in that file in our current file right here, where it says include.

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And so it's in this actual case right here is talking about the i o stream file.

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There's another C++ file.

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It is actually kind of like where we installed the main GW, if you remember from that video for Windows,

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where we installed the minimum new compiler collection, kind of where that got installed, it also

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installed some of the standard C++ library, which includes this Io stream file that has code that we

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can use.

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And so what it does is Include says, I want to include the contents of this Io stream file in my code

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so I can use stuff from it.

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So says Go search for that and put the code that exists in that file right here and just insert all

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of that code that would be in there.

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There's a lot of code that comes from this i o stream file this kind of thing from the standard template

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library.

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So it's pretty cool that you can just include that and have access to a lot of functionality from this

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file.

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So, yeah, it's including in this particular case, it's including extreme, and that is something

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that allows us to use this sea out and this in line down here as well as these operators, and we'll

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be getting to that line soon enough.

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So let's look at the next line.

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This is called using a namespace.

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So when you put this using namespace STD, it's just something that lets you use this out and inline

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without having to put something called a scope resolution operator before it and put the particular

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namespace.

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You know, it says namespace STD.

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That basically is, you know, related to this IO stream here, Io Stream is part of the standard template

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library of C++.

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And so if we don't want to have to use this in front of all of the things that we get from this.

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I stream here, then we need to put something like using namespace STD.

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It is possible to not have this line at all.

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And before the column and inline, you could just put this STD Coleman call.

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In that way, C++ would know, Oh, OK, you're trying to use something from this standard library of

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stuff that comes with C++.

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I understand now you put an STD call in calling before a see.

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Now I know what this is.

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I know where it's coming from.

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So that's the only reason we put this is just so we can kind of be a little lazy and we don't have to

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use this part right here in front of it.

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It is sometimes considered bad practice to put this in code in C++, but nevertheless you will see throughout

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the course that we sometimes just use it because we can and sometimes we won't use it.

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We'll be getting deep into what a namespace really is later, because you don't have to always put using

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namespace STD.

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You can actually make your own name spaces and things like that.

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But that's a little bit more of an advanced concept for later.

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So right now, I'm just trying to explain it in terms of like how you can use it for the STV namespace

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only.

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So that's all you need to know about it for right now.

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So this next line is us starting to define the main function.

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So what is that?

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We're talking about this line, this whole line up to here with this bracket.

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So it says and space main with some empty parentheses and open and close parentheses.

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And then we have an open curly brace.

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So we're going to take a quick detour, actually.

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I said main function and that kind of makes it necessary for me to just describe a little bit in general

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what a function even is.

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So I'm not going to go super in-depth to functions because we're going to have a separate part of the

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course just on functions.

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But I'm going to explain just enough.

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So you kind of know what this main function is.

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So what is a function of function is basically just a little sub program inside your whole program and

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your file.

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That does a specific task.

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So an analogy for this would be like if you can think of your whole program as a factory, like maybe

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a car factory.

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The function would be similar to something in regards to an analogy, like a machine that just made

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the wheels like it just does one specific thing like you make a function and it makes the wheels for

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the car.

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So something like that, you know, you can imagine it as a machine.

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That's a part of the bigger picture.

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You know, the whole factory makes cars, but it's made up of a bunch of different machines that make

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the different pieces of the car so your program can be made up of a bunch of different functions that

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handle a bunch of different tasks.

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They each are assigned a specific thing to do some work to do for your program.

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So quite often these functions, they take input data and then inside of the function, it will process

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the data or do some sort of task that you assigned it.

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You know, that task is just the code inside the function.

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So inside here, the work that main is doing is pretty much this right here.

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It's job that we've assigned it is to print out this Hello, my world, so.

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Let's go back to here, so it processes the data or does some type of task that is just the code that's

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inside of the curly braces, the open and close curly braces.

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And then quite often functions also return some sort of output data.

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So take something in, mess around with it, change it and put, you know, kind of pop something out.

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So it's like you could think of this as you know that let's go back to this car factory analogy with

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the machine that makes the wheels.

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Let's say, like you give it the materials it needs to make the wheels.

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So that's the input data.

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You give it this material, it goes into the machine.

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The machine does a bunch of fancy stuff.

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You know, maybe it like melts down some metal and shape stuff.

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I'm pretty sure this is not how car wheels are made, but you know, just for the sake of the analogy,

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bear with me.

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You know, it turns it into a wheel inside here and then it gives you a wheel.

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So material goes in.

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It makes the wheel wheel comes out.

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So that's kind of like what the function the functions do, except that this is not always mandatory.

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It can be just one or the other.

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Maybe it does not take input data.

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It might just, you know, return something to you.

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Like you could just say, hey, function, you know, give me a random number or something, and it

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would just come up with a random number and return that number to you.

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Or you might say, Hey, I'm going to give you something.

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And I just want you to take this thing and change it.

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But I don't need any new thing back after you change.

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I just want you to take this and change it.

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And maybe it changes it and does stuff in here and you don't need anything back from it, from wherever

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you.

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Sent it, you know, you sent it from some location in the code, you sent it the input material.

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And you just say, Hey, do stuff with this.

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I don't need anything back, but I want you to do stuff with it because this thing needs to be modified

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so it can be either or both can take input data and then mess with it and return stuff.

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Or it can just take in stuff and mess with it, or it can not take anything, but it still does some

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task and returns you something.

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So any of those options?

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So, like I said, there can be many functions in the C++ program.

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You could have, you know, infinitely many functions.

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But what we're focusing on now, since we're not really going over how to write our own functions,

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we're just trying to explain what this is.

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We're just focusing on main, the main function.

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So the instructions in the main function are actually special member before I said, this is a special

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name of the function.

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It is actually the first instructions to be executed when your program runs.

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So the main function is the entry point to your program.

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So it'll come here first to main and then it will start running this first line here.

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So first line to be run by the computer will be the first line in Maine as far as, like executing some

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sort of statement.

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Of course, we have this include up here.

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That's something that happens during a pre kind of processing phase when the compilation process happens.

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So but when the program's actually running being executed, it's going to come here first to do the

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actual main work of your program and it will hit this first line.