Objective-C Tutorial - Lesson 29: For Loops Video Lecture | Learn and Understand: Objective C (English) - Web Development

what's up guys join here are the
objective-c toros lesson 29 and in this
lesson we're going to be going over the
for loop and you may be saying well what
is the loop well a loop is something
that allows a set of instructions to
repeat until a certain condition is met
and loops are fundamental part of
programming and they're in most
programming languages now you should be
fairly familiar with loops because we've
been using the for in loop for quite a
few lessons now but in this lesson we're
going to be going over the for loop and
in the next two we're going to be going
over the while loop in the do-while loop
now we've already covered the for in
loop like I said and the for in loop is
actually just a special case of the for
loop and right there you can see a nice
little generic example of a for loop it
has four which says this is a for loop
and then there's something called a
counter than a condition which has to be
met and then the counter gets updated
and then there's the statements that are
are executed if the condition is true
but I'm going to be going over all this
in detail in the next two slides now a
for loop repeats a set of statements a
specific number of times as many as you
want and use the variable as a counter
to tell it the number of times to repeat
ok so how for loops work well each time
it hits the bottom of the loop it goes
back to the top of the loop to see if
the condition still applies and right
there you can see a great example of
what the top of a for loop may look like
and this is something that i really had
a hard time with when i first started
learning about loops i didn't understand
this top of the loop where you declare
some integer you assign a value and then
you say if this integer is less than or
greater than or equal to a number and
then you have this i plus plus I didn't
understand any of that for quite a while
until I read something and I don't know
just the way they explained it I was
really able to get so I'm going to try
to explain it in a really easy way to
understand it because if you don't
explain this right it can be kind of
tricky to get but like I said now I'm
going to go through this loop and how it
works in
and right there at the bottom of the
slide you can see the generic loop and
then a good example loop kind of
contrasting now the for loop in detail
so up there at the top you see four and
this tells the compiler it's a for loop
that's pretty basic all right now in
parentheses you see int I equals 1 what
you do is you declare an integer in this
case we're just going to go out I you
can call it whatever you want and then
we assign a value to it so the counter
is initialized after we do this then the
counter is evaluated when we put in I is
less than four now if this is true the
statements are executed so if I is
really less than four those statements
which in this case is just an NS log
it's executed and in this case it is
true because one is less than four now
if it is false the loose ends and the
rest of the program after the loop
continues and since it is true that NS
log it's executed next I plus plus and
if you don't remember this is an
incrementer so it adds one to the
variable of I so I is now equal to 2 and
now steps 3 through 5 are repeated until
the condition is false and then the rest
of the program continues so next I well
since I is now too because we added 12 I
it'll go through again and I'll see if
that condition is true 2 is less than
four that's correct so it'll run through
everything again I will be updated to
three then is three less than four yes
it is goes through the loop again then
it's incremented now I equals four now
and then it's four is less than four it
well that's not true that's false so it
doesn't run that NS log again it just
jumps to the end loop and continues with
the program so that's how four loops
work and that's why you have that
integer value there and then that's why
what that I plus plus at the end means
you're just adding one to it each time
you go through the loop now you may be
saying well what's really the difference
between four and four in well the
difference is that a four in Luke
doesn't have a counter like the for loop
does but simply iterates through an
array until goes through each value in
the array and you should be very
familiar like I've said already with the
for in loop because we've gone over it
quite a few times in past lessons now um
you can have a for loop that iterates
through an array how you would do it is
you would say four then you'd set up
that counter N equals one and then you
would set it that counter and less than
or equal to and then you would call the
array and then you'd call method count
and this method is for raise and it
tells you the number of elements the
array has inside of it so if this array
had ten elements in it you would
essentially be saying one is less than
or equal to 10 and that's true so then
it would run through the statement so
that's how you could use a for loop it
to do the really the same job that a for
in loop does and above the for loop is
the same as this for in loop so you can
kind of see the contrast between the two
loops but how they really do the same
job now the initialization and increase
fields are optional so you don't have to
put that counter and incrementer up
there at the top of the for loop but
even if you don't you still need to put
that semicolon before the condition so
you'd have to say semicolon eyes lesson
for semicolon parenthesis so in the
example right above you would have
already initialized the counter
someplace else in code and the increment
or increase ER is in the statements of
the for loop and the comma operator
allows you to implement some very
detailed counters for a for loop so in
this example
we have int x equals 0 y equals 10x then
the condition X is less than or equal to
Y and then the incrementer are X plus
plus so you add one each time and then
why you subtract two and then reassign
that to Y so tell me in the comments
below how many times that for loop would
run based off of that counter now now
we're going to jump into Xcode and add a
for loop to our program okay so here we
are in Xcode and you just go to the
budget object n file and how we're going
to be adding this for loop to our
program is we're going to be adding it
right here to create multiple
transactions that we can then pass
through our program and typically you
wouldn't be adding a loop to create
multiple transactions or objects in a
program you would be using a loop in
much the way that we use this loop down
here that's really how you would be
using them in a typical program but
nonetheless how we're going to be using
them we're still working with loops and
working with the mechanics of them and
we're still going to understand how they
work and everything but it's just not a
typical way that you might use them but
really that's fun but first before we
add the loop we're going to add or we're
going to begin to add a new object we're
going to call transaction then a
transaction all right now we can begin
the for loop so for int 0 SE n equals 1
then when n is less than three whoops
and then n plus plus ok and then
close out the loop now we're going to
make a few modifications what we're
going to do is since we already began
this a transaction object which is
called a transaction we can just put a
transaction right here and finish out
the declaration or yeah and then we just
have to switch all these to a
transaction and then we're going to add
a transaction obviously to this NS
mutable array that we already created up
here now you may be saying well how are
you going to do this because you're
going to run through this loop two times
based on this information up here and
you're going to create this object twice
and how is that going to work because
aren't you recreating the name and you
it may be a little confusing that's fine
if it's confusing you're not quite
understanding it because I had a lot of
problem with this and it took me quite a
while to really grasp this concept but
basically what's going on is you begin
the object declaration up here or
actually you declare the object up here
and then you just reassign values to it
down here but after each time you assign
a new value you add it to the
transactions array so let me just
comment all of this out real quickly and
go down here to the bottom and show you
a little example with variables that
makes it very easy to understand what's
going on so I'm just going to declare an
int sum number ok so saying in some
number is very much like saying
transaction a transaction right now
we're going to assign a value to some
number so some number let's say equals 2
now we're going to NS log this so some
number equals and then % I some number
now we're going to sign
the value of 3 to some number and we're
going to copy and paste that nslog now
let's see what happens if we add some
number plus some number since we assign
two values a percent I and some number
plus some number okie dokie now we're
going to build and run double quick save
all okay so as you can see the first
time we assign to just some number and
some number equals two then we assigned
a new number to it we signed three to it
and three was displayed now we added
some number plus some number and it
doesn't take the first some number which
was two and adds it to the latest some
number which was three it takes the
latest number which is three and adds it
together and so some number plus some
number or three plus three equals six so
that's very much like what we're going
to be doing up here what's going on is
that we're just reassigning the value
and then adding it to the NS mutable
array each time so we can go ahead and
delete all this and also i'm going to
put n times 100 for the value so each
time it'll be increased by 100 because n
each time will be increased by 1 so the
second time it will be two times 100 so
that's kind of cool that will add some
different up amounts for the transaction
now we can go down to our switch down
here and we need to make a few
modifications we need to change this to
loop transaction oops
and we go ahead and change this and
that's all of the modifications of the
code for this lesson so we can go ahead
and go and run save all okay now
everything built and rain correctly the
first time it was converting one hundred
dollars and then the second time two
hundred dollars and everything after
these two statements is outside that
loop that we modified so it ran just
like how it ran last time because we
didn't change anything to it so in the
next lesson we're going to be adding a
loop to this transaction and then the
lesson after that we're going to create
a new transaction and then add a loop to
that one and then we'll be all done
working with loops so thanks for
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