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Hello, and welcome to the
section 20 second challenge.

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This challenge is all about using
a std list, a doubly linked list.

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What we're going to do in
this challenge is we're

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going to simulate a playlist.

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So imagine you've got a CD and you
want to put it in your car, you

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want to play it and move to the
next song and the previous song

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and the beginning and so forth.

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We're also going to be
able to add songs to this.

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So that's the idea here.

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And we're going to model
that playlist using a doubly

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linked list of song objects.

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So I'm in the section 20 workspace.

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And here is the challenge
2 project, and then there's

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the challenge 2 solution
project, which has my solution.

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And I'll go over that
in the next video.

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So let's talk about this
challenge a little bit.

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The idea here is that you want to learn
how to use a std list, and that's what

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we're going to use in this challenge.

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We want to create a
menu-driven application.

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This would be really cool to
do graphically, but we haven't

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learned how to do that stuff.

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So what we want to do is we want
to simulate the user selecting the

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first song in the playlist and then
going to the next, the previous,

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playing forward and backwards
through the playlist, simple as that.

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We're also going to allow users
to add new songs to the playlist.

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And every time we add a new song,
it's going to be added prior

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to the currently playing song.

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Okay, so here's the menu.

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And I've got a sample run
coming over here on the right.

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And I'll go to that in just a second,
but here's the menu, play the first

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song, play the next song, play the
previous song, add and play a new

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song at the current location, and
then just list the current playlist,

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and that'll list the playlists or,
in other words, the songs that are

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out there, and it will also list the
currently playing song, and q to quit.

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So that's it.

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It's real simple.

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The available playlist is modeled
as a list of song objects.

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I'll provide the song class, and
I'll go over that in just a second.

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And these are the songs that I
put in the playlist just default.

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I just grabbed a bunch of
them from the pop charts.

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You can change these to whatever you
like or just put song one, song two,

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song three to keep track of them.

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I got kind of bored
doing song one song two.

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I wanted to see some real song names.

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So here they are.

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Drake Camilla Cabello and
Maroon 5 Imagine Dragons,

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a bunch of popular songs.

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That's it.

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So let me go over the run first.

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And then what I'll do is I'll go over
the sample code that I'm giving you.

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Over here on the right, you
can see the program running.

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The first run it just displays
the playlist right here.

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That's the playlist.

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So you can see these songs right
here are showing up right here.

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And the current song that's playing
is the one by Drake, which is

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the first song in the playlist,
you can see it right up here.

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So by default, that's
that's our starting point.

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When we first run the program,
the first song will be playing.

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Imagine you're putting
a CD in your car.

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Here's the menu, play the first song.

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So anytime you press f, it's going
to jump to Drake's song and play it.

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Next obviously, it's pretty
straightforward what's happening.

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If I'm playing Drake's song
and I press next, then it's

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going to go to Camilla's song.

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And if I press next again, The Weekend, Zedd, Maroon
5 Imagine Dragons and so forth.

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Now since we have a doubly linked
list, these songs are modeled

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as doubly linked lists, right.

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You've got your links
coming back and forth.

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And then I've got something called
current song and that's an iterator,

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that is pointing to the current song.

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So when you press next, all we're
doing is we're moving the iterator

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over here and then press again.

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Next, we're going to move it over here.

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Now what's going to be interesting
is if I'm right here at the

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first and I press previous I
want to wrap around to here.

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And if I'm over here and I press
next I want to wrap around to here.

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So I always want to
be in that playlist.

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Okay, so let's walk
through this little demo.

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Right now when we first start
the program, you can see

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the playlist and you can see
that Drake's song is playing.

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That's the very first
song in the playlist.

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If I press n or next, it says playing
next song and it says now it's playing

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the Camilo Cabello song, which is this
guy right here, never be the same.

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If I press next again, and I'm
going to scroll up so you can

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always have this in context here.

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Now it's playing the "pray for me"
song, which is the third song.

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I'll press next again.

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Now it's playing "the middle".

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When I press next again, it should
be "wait" and then "whatever it takes".

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So I'll press next again.

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Wait is playing by Maroon 5.

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One more time and now "whatever it
takes" my Imagine Dragons is playing.

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Now I'm at the end of my playlist.

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If I press next again, I want it to
wrap around back to the Drake song.

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So let's do that.

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I'll press n, and you could see
that -- let me scroll that up, you can

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see that Drake's song is now playing.

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Now if I'm here at the beginning
and I press p for previous, it

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should wrap around back down
to the Imagine Dragon song.

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So I'll press p for previous.

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Now I'm right here.

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I'm right at the end here,
Imagine Dragons is playing.

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Let me move that up for you so
you can see a little better.

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Okay, so that's it.

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Now, of course, if I press
previous here, it's going

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to go to the Maroon 5 song.

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And you can see it's
just a linked list.

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And I'm able to go around
it, which is pretty cool.

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If at any point you can press l
and that'll list what's currently

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happening, so you can see the playlist
right here that hasn't changed because

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we haven't modified it at all but

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you can see the playlist right here.

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And the current song
is the Maroon 5 song.

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So anytime you want some
information, you press l.

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All right, so now let's
get to the good stuff.

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Let's add a song.

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I'm going to scroll up
just a little bit okay.

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Now I'm going to press a.

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And when I press a, it says
adding and playing a new song.

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Cool, so what's the
song name I want to add.

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Let's say I want to add "Imagine".

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Who's the artist, it's the Beatles.

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What's my rating for the
song, I'll give it a five.

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Now when I press enter, that song
will be added before the current song.

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And if you remember the
current song was "Wait".

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That's the one that's
currently playing.

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So "Imagine" will be added
between "The Middle" and "Wait".

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So I'll press enter and it will
play. It'll be the current song.

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So I'm going to press enter
and you can see now it's

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playing Imagine by the Beatles.

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And if I list -- let me scroll up a
little bit, if i list my playlist now,

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you can see that Imagine is right here.

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Let me mark that for you with my
pen. You can see that Imagine is

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right here now and it's between Wait
and The Middle, just what I wanted.

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Now suppose I want to press f and
I want to go to the first song,

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so we're going to go here to the
Drake song and then I want to

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insert a new song before that.

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So let's do that now.

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So the first thing I'll do
is, let me clear this real

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quick, and I'll scroll up.

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So I'm going to go to the first
song, which is the Drake song.

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I'm going to press f right here.

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I'm playing Drake's song.

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And now I want to add another song.

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So let's add what's the song's name,
let's say it's New York, and let's

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say that this is Frank Sinatra.

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And I'll give it a five.

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I'm giving everybody fives.

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That's it. Now it's playing New York.

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Remember, we were at the beginning.

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So if I display my playlist, you
can see that New York has now been

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added at the beginning of the list.

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And it's playing right
here current song New York.

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That's it. That's the program.

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You press q to quit.

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Now there's a couple of interesting
things here that you can extend once

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you get this basic functionality going.

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Notice that in my menu, I have no
way to play the last song in the

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list or the ending song in the
list, you could certainly add that.

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You could add a whole bunch of other
things you can save this to file.

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You can read this
information from a file.

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So you can extend this program
in a bunch of different ways.

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Okay, so now let me show you
the source code that I'm giving you

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and that is right in here.

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I've gone ahead and included
the include files that

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you're going to need.

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And let me show you what
the song class looks like.

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It's a real simple class.

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Obviously, this is what we're
modeling, the name of the song,

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the artist and the rating, which
is an integer in this case.

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I have a friend function here, which
is my overloaded insertion operator.

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So that can display this kind
of stuff over here real easy.

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I've got a default constructor.

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I've got an overloaded constructor
here that allows me to create whatever

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I need using name artist and rating.

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Then I've got some getters that I
don't even think I'm using the getters,

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but I put them in there anyway.

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Now the most important thing we need
to do here is -- and it's not so

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important in this program, but it's
just best practice to always do.

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We need to overload these
operators, the less than operator

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and the equality operator.

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Those are the only 2 operators that
we must overload if we're going to use

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our own custom classes with the stl.

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So in this case, less than
just -- I'm defining less than as

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this -- name of this song is less
than the name of the other song.

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And the same thing with equality.

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If the 2 names are the same,
then I'm considering them equal.

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Okay, so that's that.

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Here I'm overloading the insertion
operator, as I mentioned.

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I'm giving you the code for the display
menu, which is really, really easy.

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And then I've got a couple of methods
here or functions, I should say,

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that you're going to implement.

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One is play the current song.

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And all this does is it
does this right here. Here

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we go. So I just went
forward, it says playing.

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And the song that's playing.

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That's all. It just displays that.

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And the song that's being
played is passed into it.

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So that's a really one-liner, right.

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You basically just have to
output that to an upward stream.

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Display playlist.

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Here, we're getting the entire
playlist and the current song.

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And this is the one that you're
going to call from the list

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functionality it's just going
to display all those songs.

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So in this case, we're going
to see something like this

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right here, all that good
information is going to display.

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Okay, and now here's the main.

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Probably just what you expect.

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Here's my playlist.

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That's my object, and it
is a list of song objects.

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And I'm initializing it right here.

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So that's done.

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And I'm setting my current song.

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This is the most important piece here.

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That object right there.

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That current song is an iterator
to that's pointing to some

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object in that in this playlist.

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And I'm setting it to the
beginning of the list.

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I'm setting it right to there.

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It's going to start right there.

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From that point on, it's your logic to
display the menu, get the input from

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the user depending on what they select.

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This is the guy that you're
going to have to increment or

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decrement depending on how you
want to walk across this list.

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That's it, have fun.

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Get the basic functionality
working before you extend it.

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And then you can extend it like,
I said a bunch of different ways.

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You can go to the go to the end, go
to the beginning, save it to a file.

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So next time you run this.

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You can just load the information.

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The song information from the file.

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Because remember, as it is now
every time I add a new song to the

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playlist, it's not being persisted.

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So the next time I run this,
it's not going to be there.

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So it'd be kind of nice to be able to
save that and then load it up again.

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Okay, so that's it.

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Have fun, it's a nice
little challenge project.

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It's simpler than you would think.

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Think iterators, think stl, don't
think about Is and Js and looping

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variables and things like that.

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Let the stl do the work for you.

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All right, have fun, and I'll see
you in the next solution video.