iOS 11 Developer Course Tutorial - For Loops Part 15 Video Lecture - iOS

for loops have changed a little in Swift
three and are now exclusively for
looping through arrays and they're
actually much better at doing that than
while loops let me show you how they
work so let's have a simple array again
I'll just choose some random numbers
there we go and then to loop through the
numbers in our array all we do is we
create a new variable which I'll just
call number but we can call whatever we
like so for number in array and what
that will do is loop through the array
array and allow us to access each
individual item in the array using the
number variable so we might want to for
example print number and that then gives
us eight four eight one so you can see
that's much neater and cleaner than
using a while loop
so when looping through an array I would
definitely recommend using a for loop if
you're doing something else with your
loop then probably while is the best way
forward so quick challenge then can you
create an array with four names of
friends or family and then loop through
it and print hi there and then the name
of each person so imagine this is quite
similar to printing the content of a
tweet which might be stored within an
array okay so fairly straightforward
best of luck
go for it
okay do you manage it so let's start by
creating our array so I'll call it
family members and we're gonna have Rob
Kirsten Tommy and Ralphie very simple
then we just loop through so for family
member in family members we can use any
variable name we like here but using
family member makes it fairly clear
what's going on and then we just print
hi there
add the family member and then a
friendly exclamation mark on the end
take a look there we go nice and easy
what if though you want to change these
values inside the array just changing
the family member variable won't
actually affect the array because this
has just been extracted from the array
it's not actually part of the original
array so let's say again we've got an
array of random numbers so I'll just
call them numbers this time there we go
and as before let's say we want to add
one to each of those numbers this time
we need to use a slightly more
complicated for loop and this time we
use index comma value so we're looking
for two variables this time not just one
which was effectively the value this
time we're looking for the index so
that's 0 1 2 3 4 and the value and this
time we want to take the array so
numbers
and make it enumerated which is
essentially spread it out into its
components and now we can use each of
these so index or value to get either
the location of each item or the value
itself so if we want to add one to each
of the values we can do that using
numbers and then index plus equals one
and then let's just check by printing
the numbers array again at the end and
of course it's always good to get into
the habit of using letter rather than
var but it can let you down if you then
decide you want to change the variable
or the array later on and there you go
you can see everything's one bigger now
than it was before okay so final
challenge then I'd like you to create a
simple array containing the numbers 8 7
19 and 28 and then have each of the
values using a for loop and there's a
little sting in the tail here so bit ago
and you see if you can spot what makes
this challenge a little trickier than it
might appear good luck
let's see how it goes so this I'm gonna
remember to use var rather than let
because I know this is going to change
and I'll use my array as an array name
and let's start off with eight comma
seven
come on 19 comma 28 so there's my array
then I use for index and value in my
array enumerated and now I'm gonna get
my array index and set it equal to value
divided by two so here I could use my
array index again it's the same thing as
value but I need to use my array index
here because I want to update the
original value in the array
not just the temporary value variable
that we've created here okay so you
might think that's all pretty good but
let's have a look at the results so we
should have four three point five nine
point five and 14 let's take a look ah
but instead we get four three nine and
fourteen so these two are wrong so why
is that well it's because these were
defined as integers so when we have them
they're still integers so it rounds down
to the nearest whole number so there's a
few ways around that probably the
easiest way is to rather cheekily but a
point zero at the end of each of these
numbers and then that will define them
as doubles rather than integers so when
they're halved we get the exact values
another way of doing it would be to
define
the array separately as an array of
doubles and then if you do that and then
set it equal to 8 7 1928 then you still
get the correct values because these are
doubles even though there happen to be
whole numbers all right so I hope you
manage to see through my challenge there
you'll be pleased to know that we're
almost done with our Swift to deep dive
we've got a couple of topics to look in
some detail at before we go on to build
out is it prime app the first of those
is a fundamental programming idea and
that is of classes and objects and we'll
find out what they are and how they work
in the next video