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The simplest type of
a collection is an array.

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In fact most other
complex collection types

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use arrays under the hood in some form or
another.

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We can think of an array as
a numbered list of items.

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We refer to this number as
the items index in the array.

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This allows us to identify each
item based on its location.

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For example, we can say we want
the third item in the array.

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As in most programming languages
we start counting zero.

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So the first item in the array
has an index of zero.

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The index of the second item is one and
so on.

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The end of the last item is one
less than the length of the array.

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Let's refresh our memories on
how to work with arrays and

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then learn about their advantages and
their disadvantages.

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To follow along, open work spaces and in
the consul type csharp to start the repel.

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To instantiate an array,

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we first declare the type of item
we want to store in the array.

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And then add opening and
closing square brackets.

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Here I'll give the array a name.

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I'll say lockCombination.

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Now we set it equal to
a new integer array.

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And inside this square brackets we need to
tell how large we want the array to be.

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So I'll say, three.

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One disadvantage of using an array is we
have to tell it the maximum number of

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items we expect to put in the array.

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We'll see in a bit that changing the size
of an array later is not trivial.

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Notice that all of the items in
the array are initialized to the type's

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default value.

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In the case of numeric types like integer,
it's zero.

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In the case of other types,
all of the items will be null.

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Items in a collection such as an array
are also known as its elements.

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You'll hear me use the terms elements and
items interchangeably.

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Another way we can instantiate an array

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is by initializing it at
the time we create it.

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So here in between curly braces.

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I can say 10, 5 and 32,
for my lock combination.

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When we create an array like this,

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we don't need to put the size of the array
here between the square brackets.

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The length of the array is just the number
of items in the initialization list here.

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We also don't need to specify the type
of the array when we do this.

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The type of the array can be inferred
from the types of the items, so

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long as they're all the same type.

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In fact, we don't even need to put
this new with the square braces here.

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The advantage of an array is,

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in how quickly we can retrieve an item
when we already know its index.

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So I'll get the last item in
this lock combination array and

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I'll assign it to a variable called last.

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So I'll say,
int last = lockCombination and

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then to tell it which
item in the array I want.

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I'll just put it's index here.

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Now the variable last contains 32.

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The reason retrieving an item
from an array is so fast,

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is because items in an array are stored
sequentially in the computer's memory.

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Knowing an item's index is the same as
knowing its physical address and memory.

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So, when we tell the computer we
want the fourth item in the array,

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we can find it right away without having
to count from the beginning of the array

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to the fourth item, bam!

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When it comes to accessing items,
nothing beats an array.

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The same goes for
updating items in an array.

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We're just overwriting the item
at the index specified.

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So if I wanted to change the last
item in the lock combination array.

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I just say lockCombination[2} = 20.

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Setting or updating an item in an array
when we know the index we want to set,

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is just as fast as setting a variable.

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Arrays are also good when we
want to keep our items in order.

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This makes an array a good choice for

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storing things like
combinations to a lock.

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Once we put an item at
an index it stays there.