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Now that we have all of
the classes implemented for

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each of the types of objects
we have in Treehouse Defense,

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we can use these classes
together to finish the game.

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We have a really nice set of classes,
but nothing ties them all together yet.

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We haven't yet coded up how all these
objects work together to create a game.

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So now we need to write the code for
how the game runs.

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Instead of putting the code that
runs the game in the game class,

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let's introduce the idea of a level.

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In Treehouse Defense,
a level is composed of a map, a path, and

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a number of invaders.

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Then we can create different levels
with unique maps, paths, and

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collection of invaders.

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What we do in this video is mostly review
of many of the things we've learned so

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far about C Sharp.

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So we're going to move through it quickly.

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Let's start by creating
a new file called Level.cs.

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In the Treehouse Defense namespace
we'll create a class named Level.

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The level constructor only
needs the array of invaders.

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Remember each invader already has
an instance of the path object.

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So we don't need to set the path
as a field in the level class.

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Towers aren't actually required
in order to construct a level.

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But, eventually the level
does need to know about them.

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Let's add a tower's property with
the public getter and a setter.

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So the players can set this array
after the level is created.

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Now let's make a method called play.

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It will return true if the player wins
the level and false if they lose.

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Let's use comments to scaffold
out how the game will work.

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The level will run until all
invaders are neutralized or

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an invader reaches the end of the path.

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Got an extra the there.

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First, Each tower has
an opportunity to fire on invaders.

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Then we'll need to count and
move the invaders that are still active.

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When we see the words Run until
that means we'll need a loop.

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Let's make a variable to keep track of
how many invaders there are remaining.

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The loop will run until all
the invaders have been neutralized.

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The things described by these two
comments will happen inside the loop.

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So now we'll loop through each of the
towers and let them fire on the invaders.

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Now we'll count the number
of invaders again.

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We'll reset remaining invaders to zero and
then loop through the invaders.

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We'll increment remaining invaders for
each active invader in the array.

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If the invader is active,
then we should also move it down the path.

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After the invader has moved,

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we should check to see if it's
reached the end of the path.

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If it has, we'll return false
signifying that the user lost.

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So we'll check invader.hasscored.

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Finally if all invaders
are neutralized then the loop will

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exit because remaining
invaders will be zero.

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Then we'll return true
signifying that the user won.

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So this is the end of the loop here.

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So here we return true.

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As we look at this method,

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it isn't entirely obvious on the surface,
what returning true or false means.

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We can provide that information in
a comment here at the top of the method.

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So I'll say Returns: true if

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the player wins, false otherwise.

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We just wrote a ton of code.

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Be sure to read through this code
carefully to make sure that you understand

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what it's doing.

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You can always watch this
video again if that helps.

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Finally, let's compile to make sure that
we haven't introduced any compiler errors.