iOS 11 Developer Course Tutorial - Arrays Dictionaries Part 11 Video Lecture

okay so moving on from integers strings
doubles floats and boolean x' we're now
going to look at a whole new type of
variable and that is the array so
imagine you're making a Twitter clone
and you want a way of displaying
people's tweets you need to store that
tweet content somewhere and what you
don't want to do is to have to create a
new variable for every tweet that's
created otherwise you'd have tons of
different variables with all sorts of
different variable names that would be a
nightmare to keep track of so that is
where you would use an array so we'll
create one like this we use the square
brackets near the Enter key on your
keyboard and then we're going to have
several different values in our array so
we might have ages of people in our
family for example say 35 36 5 and 2 so
separated by commas and this array then
takes those four values and they're all
stored within the array so the obvious
question what if we wanted to get at one
of those particular values well all we
do so say we want to print one of those
values to the console we use square
brackets again and then we refer to the
location of the item within the array
and there we go
so we've got the number five printed
there which is perhaps not what you were
expecting you might have thought that
the second item in this array would be
36 but actually array counting starts at
0 so if you wanted to get that 35 out of
this array you would print array 0
rather than array 1 so now we can create
arrays and we can get the values from
them we can also work out how many items
there are in an array if we wanted to
add an item on the end we would use
array dot append and then just add on
the new element so
that might be a one for example and then
the array would have a new element on
the end and there it is
similarly we can remove elements from
the array so we can remove all remove
last remove first or we could remove a
particular item so if we remove at one
for example which item would that remove
it would remove the 36 we can also sort
an array very easily just using array
sort and that will then sort all the
items in the array in numerical and
alphabetical order
there we go and finally if you want to
view the contents of an array in the
console you can just print it and that
will show you the array and all the
elements in it okay there's lots more
that we can do with a race but I'm going
to leave it at that for now and just
give you a quick challenge so I'd like
you to create an array with the numbers
three point eight seven seven point one
and eight point nine in it and then
remove seven point one and append to the
end of the array the product of the two
remaining elements ie three point zero
seven x
eight point nine that's it so do it
looking at these or not as you need to
but best of luck
go for it
all right should have been fairly
straightforward I'm gonna create an
array called my array I'm using var this
time because I'm going to need to remove
an item in the array and let's add in
these numbers so three point eight seven
seven point one and eight point nine
next we need to remove the middle one so
we do that using my array dot remove at
and we want to remove the one with
number one because remember goes zero
one two and that's removed at the seven
point one for us and then finally let's
append that last value so my array dot
append and we want to multiply the two
remaining values together so we're going
to take my array 0 multiplied by my
array my array 1 there we go so now we
should have the two original values
three point eight seven and eight point
nine and then the multiple of those two
contained in the third element in the
array okay
we're saying briefly that arrays don't
have to contain numbers they can contain
strings or any object you like and they
can even contain a mixture of those so
we could for example contain a string a
number and the boolean all in a single
array quite often though we want to
specify the particular type when you
create the array because it's not
usually a great idea to have different
types in a single array and you can do
that but let's say we want to have an
array of strings we could create that by
just putting the variable type inside
the square brackets and then having a
pair of parentheses at the end and this
essentially means create an array which
will contain some strings but at the
moment as we can see here is an empty
array so we'd have to use append or one
of the other methods to add a value to
it okay that's more or less all you need
to know about arrays right now so let's
move on to a slightly different type a
variable and that is the dictionary and
a number of other programming languages
don't have dictionaries so even if you
program before you might not have come
across the dictionary so let's see what
they are if we create our dictionary and
what we do is we create it in much the
same way as we did our array with our
square brackets but each item in the
dictionary now has a key so for example
we might define a computer for some of
us as something to play call of duty on
and now we've defined the computer field
within the dictionary array to have the
value something to play call of duty on
similarly we might define coffee as the
best drink ever ever so this is
something of a literal dictionary where
we have a particular word and then we
have the definition of that word of
course that doesn't have to be what we
use dictionaries for but if we did set
it up that way we could then get one of
those values by using dictionary and
then the key or the name that represents
that so dictionary computer would then
be something
to play Call of Duty on and now here you
can see we've got this word optional
which came up in a previous section and
here we're going to look at it in a
little bit more detail and then later on
in this section we'll really dive into
what these optionals are but right now
if I use dictionary and then the key
computer I know that it has a value
because I define that but if I try and
use dictionary house for example to try
and get the value for the house filled
inside this dictionary you can see I get
the result nil now if I try and set that
equal to the text of a label for example
or if I try and display that word on the
screen that's going to give me an error
we need to be very careful about using
things like this unless we're absolutely
sure that this has a value so a
dictionary computer I know for sure that
it has a value because I just defined it
up there so if I know absolutely for
certain that it has a value I can use
the exclamation mark to what's known as
unwrap it and this is basically a way of
telling Xcode that don't worry I know
absolutely for sure that dictionary
computer has a value because I've
defined it up here if you turn out to be
wrong Xcode will punish you with a
complete crash so you do need to use
these very sparingly and very carefully
only when you're absolutely certain that
this has a value we'll see some better
ways of dealing with optionals which let
you test whether or not it has a value
before using it later on in this section
and for now we'll leave it as an
optional we can use dictionary dot count
just as we did with array dot count soda
true count would be two is the answer
because there are two items in this
dictionary we can add extra values we
don't append them like we did with
dictionaries we just set them in the way
that you might expect
we set Dictionary dot pen for example
equal to old-fashioned writing implement
and that will then add it directly into
the dictionary with the key pen aha can
you see why I've got an error there it's
because I define dictionary with a let
which means it's immutable or can't
change so I need to update that to a var
which will allow me to add items in
there I can also remove items from a
dictionary using tonight Dictionary dot
remove value for key and so if I want to
remove the computer value then I just do
it like that
and similarly like an array I can print
a dictionary and see the values in the
console there we go so what we've got
left is pen and coffee and also just
like we could define empty arrays like
this we can define empty dictionaries so
if for example I had a dictionary of
game characters which was going to store
the strength of each type of character I
might use a string to represent the name
of the character and then a double to
represent the score and then I could
create my dictionary just like I did
with my string array down there and if I
wanted to add for example a ghost which
has a strength of I don't know eight
point seven and I would just do it like
that but of course
would have to create my game characters
dictionary with a VAR to allow me to add
a value to it
okay and notice there as well as I
mentioned briefly in the previous
section doubles and floats are not
absolutely precise so this is pretty
darn precise and if you actually try and
use it anywhere in your program it will
be precise enough you won't get that
rounding error here but often when you
actually print doubles you'll see
they're not exactly what they're
supposed to be if you want a value which
is exactly correct
you can use the decimal type and then
you'll see that this value updates to
precisely eight point seven there we go
but floats and doubles are much more
widely used mostly because they're a lot
faster and a lot more efficient okay so
that's pretty much all you need to know
about dictionaries for now let's set you
a challenge to give you a quick bit of
practice with dictionaries I'd like you
to set up a menu dictionary which has
three items on it Pizza which will cost
1099 ice cream which will cost $4.99 and
salad which will cost $7.99 then I'd
like you to take two of those items
whichever they are and print the total
cost of my meal is and then work out
what that is using the elements in the
dictionary okay pretty simple best of
luck go for it
okay let's give it a go then so I'm
gonna use let because we're not going to
be editing this dictionary after we've
created it so we're going to have pizza
which is a string so I've put it in
double quotes there and that's going to
have a value of 1099 which is a float or
a double in fact so I'm not going to put
it in quotes absolutely I forgot the
variable name so menu is equal to pizza
which is 1099 ice cream which is $4.99
and salad which is $7.99 so now we've
created our menu and then it's a temp to
our print statement so the total cost of
my meal is and I'm going to choose pizza
and ice cream so to get the cost of a
pizza I need to use menu and then pizza
and I need to force unwrap that to show
that I'm sure that this has a value and
then I'm going to add to that menu ice
cream
and I need to force unwrap that as well
which I'm happy to do because I defined
it up here so I know it has a value and
there we go
you can see the total cost of my meal is
1598 exilim so now that's all we need
for dictionaries and also arrays and
those are all the fundamental data types
that we'll be using in how IRS
development and in this course in
general next then we're going to look at
our first basic Swift programming
construct which is the if statement so
we'll see how they work and how we can
use them to have more power to our code
and then we'll be putting everything
that we've learned together to create a
simple game how many think is