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Arrays
5:22Collections of objects can be stored in an array.
[MUSIC]
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Up until now we've been dealing
with individual objects.
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Tree house Defense will need to be
able to deal with groups of objects.
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For example, we'll have many towers and
many invaders.
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It'd be pretty difficult to keep track of
all of these objects if we had to create
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a separate variable for each tower and
give each variable a different name.
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What we need is to be able to keep track
of them as a collection of objects.
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There's a lot of ways to
represent a collection of objects.
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The simplest is an array.
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You can think of an array as
a numbered list of items,
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we refer to this number as
an items Index in the array.
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This allows us to identify each item
based on its location in the list.
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For example, we can say we want
the third item in the list.
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Remember how we learned earlier if we
start counting at zero in programming.
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Well, we do that with arrays and
other collections, too.
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So the third item in the list
actually has an index of 2.
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Let's learn how to work
with arrays in C Sharp.
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To learn about arrays,
let's open the C Sharp Rebel.
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To open the C Sharp Rebel in workspaces,
just type C sharp in the consul.
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To demonstrate how to create an array
let's create an array of strings.
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To do this, we first specify that the type
of objects we want to store in the array.
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In our case, it's string.
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To make this an array of
strings we had opening and
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closing square brackets
here after the typing.
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Then we give the array of name.
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I'll call it favoriteThings.
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The square brackets here
signifies that this is an array.
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We just declared a string or a variable,
but we haven't put anything inside it yet.
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In fact it isn't even an array yet
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to see why type the variable name
favoriteThings in the C Sharp repo.
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It printed out null.
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Null has a special meaning in C sharp.
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It represents the absence of a value.
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For most types, when we declare
a variable without assigning anything,
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it's set to null by default.
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The exception to this rule is
numeric types and struct types.
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Numeric types such as int and
double have a default value of zero.
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We'll learn about struct
types in future courses.
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A string array is just
another type of class.
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In order to create one we
need to instantiate it.
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We do this similar to the way we
instantiate any other type, by using new.
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Only, we don't need to provide
parentheses at the end.
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We do need to specify how
long the array should be.
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We put how many items arrays can hold
right here between the square brackets.
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I'll make it three items long.
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We have an array that
can hold three strings.
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To see what we did,
type favorite things in the console again.
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What we're seeing is
the contents of the array.
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As you can see, everything is null.
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But now there are three nulls,
one for each item in the array.
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Their null because we haven't said what
we want our three things to be it.
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There are a couple ways we can do that.
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First, we can set individual items.
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Let's set the first item
in the array to sunshine.
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We do that by first saying which index
in the array we want to change and
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then assign it a value.
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Notice that I type the index, 0,
right here in between the square brackets.
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Let's take a look at the array now.
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Now the first item in the array
has been changed to sunshine.
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We can get the value from a specific
location in the array like so.
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By using index zero,
we're getting the first item in the array.
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Sometimes we want to set all of the items
in the array at the same time that we
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declare it.
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We can do that by using curly braces at
the end here, with commas between them.
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So here where we're declaring the array,
I'll type sunshine,
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presents, and babies.
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Let's see what our array looks like now.
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Now we have three items in the array and
none of them are null.
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There's an easier way to do this because
we're providing the list of items
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here when the arrays created.
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The compiler already knows
how many items we want in it.
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So we don't need to type three again here.
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In fact, we can make this even shorter.
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All three of our items are strings,
and the compiler knows this.
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So we don't need to specify the type here.
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Arrays are so common that Csharp has an
even shorter syntax for initializing them.
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We can delete the new keyword and
the square brackets and
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just list the items inside
the curly braces like so.
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Finally, we often want to
know how long an array is.
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For that,
we can type favoriteThings.Length.
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This will always give us
the full length of the array
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that includes any null items too.
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Now that we know a bit about arrays
let's put them to work for us.
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