iOS 11 Developer Course Tutorial - If Statements Part 12 Video Lecture

continuing then with our deep dive of
Swift we've now looked at various
different types of variable as well as
arrays to store multiple variables and
dictionaries to match keys with variable
values so now we're going to move on
from variable types and look at if
statements and they are an absolutely
fundamental part of programming in any
language and in Swift they work
extremely simply so let's say for
example you've got an app that for
whatever reason you need to be over 18
years old to play then we might have a
user with an age of 13 and we want to
check whether that user is over 18 or
not obviously when the app is running we
wouldn't know in advance what the age of
the user is going to be so we need to
test this out and we can do it by using
if and then the variable name and then
if we want to check that they're over 18
then we look for age being greater than
18 and then we use these curly brackets
to contain the code for whatever we want
to do if this statement is true so for
now we might just print you can play
if the users not over 18 we can use an
else statement to do something if this
statement is not true so we might print
you're too young so there we go so at
the moment it's printing you're too
young if we change the age to 21 though
then we get the result you can play so
this is if the age is strictly greater
than 18 but what we normally mean when
we say over 18 is actually 18 or over so
at the moment if you put in your age as
18 it will come up as too young because
we're checking for when the age is
actually bigger than 18 and 18 is not
bigger than 18 so if we wanted to change
that we would make it so that age was
greater than or equal to 18 and then 18
year olds would be allowed to play so
that's now a greater than or equal to if
statement so that's the basic idea
that's how if statements work what if we
wanted to check someone's user name so
we might have for example a variable
called name which we might set equal to
Kirsten then we might want to only let
people call Rob play our game then we
can check to see if name is equal to and
now the fiddly bit with equal to is that
we need to use two equal signs and this
is because if we use one then what that
actually does is set the variable name
equal to Rob and it actually returns a
true statement so we'll get an error
here because
we're trying to change the value of name
to rob so setting a variable to a value
is different to checking whether the
variable is actually equal to that value
and to make it clear which one we want
to do if we want to check then we use 2
equals like that incidentally if we want
to check that a name is not equal to Rob
we use exclamation mark and equals and
that's a fairly standard usage across a
number of different languages as well so
here we might want to say hi the name
you can play and if that's not true we
could print sorry name
you can't play so at the moment it's
cursed and sadly cannot play but I can
alright we can even combine more than
one if statement together so we can look
at two if statements and we can join
them together with an and so let's for
example my game is even more selective
than it's been so far so you have to be
robbed and over 18 then we would check
for if name is equal to rob and and we
use a double ampersand or a double and
symbol shift 7 on my keyboard to
represent and hand
so if name is equal to rob and age is
greater than or equal to 18 then we'll
print you can play and this time I'm
also going to show you that we can add
an if statement to the else field so we
can look at else if so if just one of
those is true name is equal to Rob for
example then we might print sorry Rob
you need to get older so if we now
change the age say back down to 13 then
both of these are not true so we won't
get that you can play but the name is
still Rob so we should get a nice
friendly message for Rob there we go so
you can have as many of these if-else
statements as you like keep on going as
needed we can also double up our if
statements
with an or between them so say I wanted
to get a bit selective and allow either
Rob or Kirsten to play my game and I
could set if name is equal to rob or and
the symbol for or is a bit of an odd one
it's a double pipe and the pipe conducts
lash for me just above the left shift
key so you need two of those to
represent an oar and then we'll check
for name at being Kirsten and then if
either of those are true we might say
something like welcome and then the name
and of course you can combine as many if
statements as you like it starts to get
a bit complicated but you could put
whores and then hands and you can have
as many statements as you like all along
that line if you really want to all
right just one more thing to show you
and that is how we can use boolean x'
with if statements and they actually
work really nicely if for example we
have a boolean called is male and we set
that to be true then we can use that
directly in an if statement so we can
use if he is male and then have the
result which might be something like
your mail coming out there
and we don't need to have his mail equal
to true that will still work but we
don't need it when you've got a boolean
you can just put that billion directly
into the if statement there okay so
that's all we need to know about if
statements for now of course I'm going
to give you a challenge to put all of
this together
and the challenge is going to be to
create a login system so I want you to
create a username and password variables
with values you can choose whichever
values you like and then I want you to
use if statements to check those against
the supposedly correct username and
password and give the user feedback to
tell them if they are correct so that's
a one option or possibly they're both
wrong the username and the password
three just the username is wrong or four
just the password is wrong so I want you
to work out either are the values
correct are they both wrong is just one
of them wrong and then which one it is
okay simple as that
best of luck go for it
all right hope you got them I'm going to
create a variable called username which
will be equal to rob Percival and that
will be the correct value and then a
password
I'll set equal to my pass and then first
off I'll check for them both being
correct
so if username is equal to rob Percival
and password is equal to my pass then or
print your in you've logged into the
system so else let's check for both
being wrong to see if a value is
different to another value we use
exclamation mark and equals and that's a
fairly standard approach from all
programming languages well then if you
were able to give that a quick google
and figure it out for yourself or if you
knew it from any other language so if
the username is not equal to rob
Percival and the password is not equal
to my pass then we'll print both
username and password are wrong and then
now I'm going to be a little bit lazy
and rather than checking for both
username and password I'm just going to
check for the username being correct so
if the username
is equal to rob Percival well that means
that the username is correct but we know
that they're not both correct
because otherwise we would be here and
we're not so it must be that only the
username is correct so we'll write
password is wrong and then for the last
one I'm gonna be even lazier and I'm not
even going to check because there's only
one more option
so a final option if we get to here it
must be the other option which is that
the username is wrong okay so I hope you
got something like that don't worry if
you did a double check every time that's
not a problem but do always try and find
the most efficient ways to code and
solve a problem so the moment you can
see we've got your in let's see what
happens if I get the username wrong then
we get username is wrong excellent
if I get the password wrong as well then
we get both username and password are
wrong and if I now get the username
right but the password wrong we get the
correct message there as well wonderful
so well done for sticking with me we've
done some heavy coding over the last few
videos now you'll be relieved to hear
we're going to move away from
playgrounds and back to core Xcode and
we're gonna make a new app a game in
fact and it's going to be a simple
guessing game called how many fingers