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Collections of objects can be stored in an array.
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[MUSIC]
0:00
Up until now we've been dealing
with individual objects.
0:04
Tree house Defense will need to be
able to deal with groups of objects.
0:08
For example, we'll have many towers and
many invaders.
0:13
It'd be pretty difficult to keep track of
all of these objects if we had to create
0:16
a separate variable for each tower and
give each variable a different name.
0:20
What we need is to be able to keep track
of them as a collection of objects.
0:25
There's a lot of ways to
represent a collection of objects.
0:31
The simplest is an array.
0:34
You can think of an array as
a numbered list of items,
0:37
we refer to this number as
an items Index in the array.
0:40
This allows us to identify each item
based on its location in the list.
0:44
For example, we can say we want
the third item in the list.
0:49
Remember how we learned earlier if we
start counting at zero in programming.
0:54
Well, we do that with arrays and
other collections, too.
0:58
So the third item in the list
actually has an index of 2.
1:02
Let's learn how to work
with arrays in C Sharp.
1:06
To learn about arrays,
let's open the C Sharp Rebel.
1:10
To open the C Sharp Rebel in workspaces,
just type C sharp in the consul.
1:13
To demonstrate how to create an array
let's create an array of strings.
1:18
To do this, we first specify that the type
of objects we want to store in the array.
1:22
In our case, it's string.
1:27
To make this an array of
strings we had opening and
1:29
closing square brackets
here after the typing.
1:32
Then we give the array of name.
1:35
I'll call it favoriteThings.
1:37
The square brackets here
signifies that this is an array.
1:39
We just declared a string or a variable,
but we haven't put anything inside it yet.
1:43
In fact it isn't even an array yet
1:47
to see why type the variable name
favoriteThings in the C Sharp repo.
1:50
It printed out null.
1:58
Null has a special meaning in C sharp.
2:00
It represents the absence of a value.
2:02
For most types, when we declare
a variable without assigning anything,
2:05
it's set to null by default.
2:08
The exception to this rule is
numeric types and struct types.
2:10
Numeric types such as int and
double have a default value of zero.
2:15
We'll learn about struct
types in future courses.
2:20
A string array is just
another type of class.
2:23
In order to create one we
need to instantiate it.
2:26
We do this similar to the way we
instantiate any other type, by using new.
2:29
Only, we don't need to provide
parentheses at the end.
2:34
We do need to specify how
long the array should be.
2:38
We put how many items arrays can hold
right here between the square brackets.
2:41
I'll make it three items long.
2:46
We have an array that
can hold three strings.
2:48
To see what we did,
type favorite things in the console again.
2:50
What we're seeing is
the contents of the array.
2:55
As you can see, everything is null.
2:58
But now there are three nulls,
one for each item in the array.
3:00
Their null because we haven't said what
we want our three things to be it.
3:04
There are a couple ways we can do that.
3:09
First, we can set individual items.
3:12
Let's set the first item
in the array to sunshine.
3:14
We do that by first saying which index
in the array we want to change and
3:18
then assign it a value.
3:21
Notice that I type the index, 0,
right here in between the square brackets.
3:28
Let's take a look at the array now.
3:33
Now the first item in the array
has been changed to sunshine.
3:37
We can get the value from a specific
location in the array like so.
3:41
By using index zero,
we're getting the first item in the array.
3:48
Sometimes we want to set all of the items
in the array at the same time that we
3:52
declare it.
3:56
We can do that by using curly braces at
the end here, with commas between them.
3:57
So here where we're declaring the array,
I'll type sunshine,
4:02
presents, and babies.
4:10
Let's see what our array looks like now.
4:17
Now we have three items in the array and
none of them are null.
4:19
There's an easier way to do this because
we're providing the list of items
4:23
here when the arrays created.
4:27
The compiler already knows
how many items we want in it.
4:29
So we don't need to type three again here.
4:33
In fact, we can make this even shorter.
4:36
All three of our items are strings,
and the compiler knows this.
4:39
So we don't need to specify the type here.
4:43
Arrays are so common that Csharp has an
even shorter syntax for initializing them.
4:47
We can delete the new keyword and
the square brackets and
4:53
just list the items inside
the curly braces like so.
4:56
Finally, we often want to
know how long an array is.
5:00
For that,
we can type favoriteThings.Length.
5:04
This will always give us
the full length of the array
5:12
that includes any null items too.
5:16
Now that we know a bit about arrays
let's put them to work for us.
5:18
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