iOS 11 Developer Course Tutorial - While Loops Part 14 Video Lecture -

so now we're gonna move back from our
how many fingers gain and we're going to
go back into our playgrounds and find
out about loops so think back again to
the Twitter clone that I mentioned a
couple of videos ago and ask yourself
how you would write the code to display
all of those tweets you don't want to
write the code out separately for each
tweet that would be madness so what you
have is something called a loop which
allows you to run the same piece of code
several times and for example display
all of those tweets now there are two
type of loops and the first one that I'm
going to show you is called the while
loop and it works like this so we
usually start with a variable which is
often called I it's going to be our
counting variable as we go through the
loop and we'll set it initially equal to
one it could be anything but one's a
good starting point and then we're going
to use the Y or command and we're going
to keep going as long as I is less than
10 so next to the while command we put
our condition that has to be true for
the loop to continue and then each time
the loop goes round we're going to add
one to I which we can do using I equals
I plus one and now you can see that that
happens nine times and if we then
printed the value of I each time to the
console and we'll see that we start off
with I is equal to one and then each
time we go through this loop one is
added to I so we get one two three four
five six seven eight nine we don't get
10 because this loop continues as long
as I is less than ten if we wanted to
include the ten we would change the
command to I is less than or equal to 10
and then that's included so that's the
idea of a basic while loop we can use an
abbreviated form of I equals I plus one
which is AI plus equals one and that
does exactly the same thing but it's a
little bit neater you may have seen in
previous versions of Swift or other
languages the command I plus plus which
in many languages does the same thing as
I plus equals one but that has been
taken out of Swift three so if you want
to increment I increase it by one you
need to use I plus equals one okay quick
challenge then can you use a while loop
to display the first twenty numbers in
the seven times table simple as that so
starting at seven ending with 140 can
you display the first twenty numbers in
the seven times table using a while loop
go for it
did you manage it should be fairly
straightforward we'll set our I variable
back to one again and then we want the
first 20 numbers so I'm gonna keep going
as long as I is less than 20 I'm going
to add 1 2 I each time and then the only
major change I need to make from what we
did before was to multiply I by 7 each
time when we print it and there we go so
now we get 7 14 21 28 etcetera all the
way to 140 another way to have done it
would have been to keep going as long as
I is less than or equal to 140 and then
just print I and then add 7 to I every
time and then we need to change the
starting point to 7 and then we'll get
the same effect
so either way round gives us the 7 times
table another challenge for you this
time
I'm going to set up an array so it's
going to be just a very simple array of
some random numbers or integers there we
go and I want you to use a while loop to
add one to each of the values in the
array now that's quite tricky
let's see if you can figure out how to
do it
good luck did you manage it I hope so
we're going to start by setting I has 0
this time because the first item in the
array is the 0th item and then we're
going to keep going as long as I is less
than and we've got 1 2 3 4 5 6 items in
the array so we could put when I is less
than 6 and that would work fine but the
slightly fancier way of doing it would
be to keep going as long as I is less
than array dot count which will give us
the same number but this code would then
automatically adapt if I added extra
numbers in and I wouldn't have to
manually change that number there so
then as before we'll add 1 2 I each time
and if we want to add one to each of the
values in the array we just use array I
plus equals 1 and of course you may have
spotted this yourself we'll need to set
array to a var to allow that to work and
then let's just quickly check we print
the value of the array at the end we
should have 8 24 99 to 1 and 764 and
there you go there it is
so we can use while loops to just loop
through chunks of code on their own or
we can loop through an array and do
something with each of the elements in
the array great that's all you need to
know about while loops for now in the
next video we're going to go on and look
at for loops and see why they are
general
the better choice for doing this sort of
loops when we're looping through an
array and getting all of the values out
so you how to do that in the next video