Part 15 - C# Tutorial - for and foreach loops in c#.avi Video Lecture -

- welcome to presume technologies I'm
rented this is part 15 loops and c-sharp
in this session we will be talking about
four and for each loops in part 13 we
have seen while loop and in part 14
do-while loop let's look and look at an
example now for understanding or loop to
do that I'm going to create an integer
array so end numbers and if you're new
to arrays please check my video tutorial
on arrays so I'm going to create an
integer array whose size is 3 and I want
to initialize this array with 3 elements
so numbers of 0 0 1 okay so we have
initialized this array with 3 elements
okay now if I have to pull elements of
this array and print them there are
several ways to do that I can make use
of while for loop and for each loop okay
to compare and contrast the differences
between while and for loop let's do that
with while loop fast and then we will do
it with the follow so to do it with
while loop I'm creating a variable of
type integer into I is equal to zero
which is going to act as a counter for
us to loop through the array while I is
less than numbers numbers is nothing but
the array numbers dot length so while I
is less than the length of the array and
if you look at the length of the array
it's three so we zero less than three
that's true that's true I want to print
the elements in that hair is own numbers
of I and then I need to increment the
value Phi okay so if you look at this if
I go ahead and run this program it
prints out one zero one one zero two one
zero three all the elements out of the
salad so let's look at this well what's
happening I'm using a counter here I
which is initialized to zero okay is
zero less than three true so it gets
into the while loop numbers of I am
numbers of zero at position we have 1 0
1 so it prints 1 0 1 and increments the
value of I by 1 so I becomes 1 so it's 1
less than 3 that's true
so print the number at numbers of 1
location which is 1 0 2 it prints 1 0 2
increment value by 1 so it becomes 2 is
2 less than 3 that's true it gets inside
numbers of 2 is 1 0 3 which gets printed
increment the value of I by 1 so I
becomes 3 is 3 less than 3 that's false
so it gets routed to loop and that's how
it's printing that so if you look at the
while loop here we are doing the
initialization here we are doing the
condition check here and we are
incrementing the variable here so we are
doing you know initialization here
condition check here incrementation
incrementing the variable here but
whereas if we have to do the same thing
using for loop let's see how to do that
so 4 and J equal to 0 J less than
numbers dot length 3 plus plus and
numbers off J so if you look at this for
loop we are doing the initialization ok
you have to say console.writeline
console.writeline numbers okay
if you look at this for loop we are
doing the initialization here condition
check here and increment all with the
for loop but it will look it slightly
different but the fundamental principle
behind
looking through the elements is the same
we need a variable we need a counter we
need a boolean expression and we need to
increment the variable that's
participating in the boolean expression
in a while loop we do it at different
places but in the for loop we do it at
the same place that's the only
difference so now if we go ahead and run
this program the output should be
essentially the same so it's 1 0 1 1 0 2
1 0 3 this is printed by the for loop
and this is printed with while loop ok
so a for loop is very much similar to
the while loop in a while loop we do the
initialization at one place condition
check at another place and modifying the
variable that participates in the
boolean expression at another place
whereas for loop we do all of these in
one place ok now if I have to do the
same thing using a for each loop let's
see how we do that so the way we do it
is for each now for each loop is
basically used to iterate through a
collection for example if I have a
collection of numbers or collection of
strings a collection of date times
whatever may be the data type if I have
a collection of something I can actually
do that collection using foreach loop
very efficiently ok there is no
possibility of you know index out of
range exceptions when you actually use
for each loop you don't have to know how
many elements are there within that
collection for example if I have to use
the for loop and loop through the
elements within this collection within
this this is an numbers collection I
mean this is an integer collection
numbers isn't it it's an array of type
integer so it's it's a collection of
integers if I have to loop through this
integer collection then I have to know
how many elements are there within this
side otherwise there is a chance of you
know index of the planes exception but
whereas if you are using a for each loop
you don't have to know how many elements
are there you can tell you for each loop
to loop through the collection as long
as there are elements within that
collection let's see how to do that now
we know that numbers is an integers
collection so for eat and let's say K in
numbers so what's going to happen the
for each loop we'll go ahead and look at
you know this collection it takes the
first element of this collection and
puts it in this variable and we can do
whatever we want with that variable so
let's say I want to print the value
within that variable and now if I go
ahead and run this Lord would will be
exactly the same except that you're
using for each loop here so look at this
there is no counter nothing you know all
we are doing is float each element from
the collection stir it in this variable
and do whatever you want and then do
that as long as there are elements of
this collection switch very easy and
there is I mean when you use for you
don't have to know how many elements are
there in the collection
you just have to iterate through them if
you look at this one it just prints 1 0
1 1 0 2 1 0 3 etc ok pretty easy and
there is no chance that you know you can
actually get any type of index out of
range exception but on the other hand
with a for each loop
well maybe the for loop you have to know
how many times you have to loop to it
depending on the length of the array by
mistake you know if it's a type of let's
say an instead of saying less than I'm
saying less than or equal to if you look
at the size of this numbers array it's
actually 3 and we are starting at 0 from
0 to 3 it's like 4 elements but if you
look at the array we only have 3
elements within that now if I go ahead
and build this and if you look in the
status bar will succeeded I don't get
any compile time error but actually when
I run this I get a runtime exception
look at this system dot index out of
range exception ok there are only three
elements within this collection but I am
looking for the fourth element because
I'm starting at 0 and then I'm looking
at the fourth element okay so this is
just a typo I didn't knew about this it
compile time at run time you know it's
trying to pull full Dell
from the array which does not exist and
we have this index trained exception
okay so if you don't know it how many
times you have to loop exactly
you risk in all risk getting these index
or the flame exceptions but whereas with
for each loop you don't have that
problem you know it repeats as long as
there are the elements in this
collection let's say for example later
another element gets added
you know maybe numbers 3 equals 1 0 4
you have to bump the size of the array
to 4 now if I go ahead and run that I
don't have to make any modification to
my body to do it just going to loop
through this collection as long as there
are relevant so there are 4 elements now
it's going to loop to 4 times and print
all the four elements so that's the
advantage of for each loop so if you
look at it for each loop if for each
loop is used to iterate through the
items in a collection for example for it
to loop can be used with arrays or
collection classes and system
collections namespace in dotnet version
1.0 we have system collections like
ArrayList hash tables tag queue etc ok
so we can use for each loops with them
we can also use for each loop with
generics we can use for each loop the
turrets with any type of collection you
can basically use a for each loop we
will talk about system dot our net
framework 1 1 0 collections and generics
in a later session
alright so before we wind up I also want
to talk about two very important
keywords you know when it comes to
working with loops break and continue we
have already seen one implementation of
break you know in the switch and we were
talking about switch statement we have
seen that if we use break statement in a
switch in any of the case statements you
know the control will jump out of the
switch statement there is another use of
a break statement you know if you are in
a for loop or any kind of you for that
matter for while while for each whatever
loop it is for some reason if you want
to get out of the loop you can use the
break keyword let's see that ok for
into I is equal to 1 I less than or
equal to 20 I plus plus let's say I want
to print the value of I so control dot
write line I so if you look at this
there's a pretty simple program what is
that's going to do this is going to
print numbers from 1 till 20 let's say I
want to print only until 10 but I don't
want to modify this condition if that's
the case you can actually F I is equal
to if I is equal to 10 just say break
and look at this as I type break
you know this is highlighted as well
meaning that you know this break
statement causes you to get out of this
for loop so let's see so now what are we
doing here okay starting at 1 and I less
than or equal to 20 print this but then
if I is equal to 10 we are saying break
so what happens when I becomes 10 this
break statement gets executed then this
is executed it comes out of the for loop
and it gets out in for loop the program
terminates and only until 10 will be
printed so keep in mind break can be
break statement can be used in two
contexts okay when you are working with
a switch statement you know if any of
the case statements have a break break
statement there it causes the control to
get rid of that switch statement if you
use a break statement within a for loop
or any loop for that matter it causes
the control to get out of that loop okay
so if I run this it's going to print
until 10 and as soon as 10s reach you
know this condition becomes true it gets
you to the for loop so the rest of the
for loop will not be executed that's
about the break statement let's look at
another statement which is continue
keyword okay when do we use continue
keyword
now let's say I want to print even
numbers case if I have to print even
notice let's start at 0 let's say I want
to print even numbers and I want to
print even numbers only until 20 for
example oh I'm sorry
only until 10 or I want to print the
even numbers until 20 but I don't want
to increment the value by 2 okay if I
run this program Asus it's going to
print numbers from 1 from 0 till 20 but
I want to print only even numbers until
20 so how do I do that so if I mean
there's several ways to do it the
simplest way to do that is obviously
instead of saying I plus plus we can say
is equal to I plus 2 so if I go ahead
and run that it's gonna print even I
will still 20 but since I want to
demonstrate the importance of the
continue keyword we will do it in a
slightly different way okay so if I 1 2
is equal to 1 so if I divided by 2 is 1
then I'm saying continue okay look at
this again the for loop is highlighted
okay so what what what does this
continue key will do okay if you look at
this program it's actually a 3 line of
program a very simple program and we are
starting at 0 and and then less than or
equal to 20 including the value of i ok
is 0 divided by 2 is equal to 1 now it's
equal to 0 so this statement will not be
executed so it will come here prints 0
and then comes here increment the value
of I by 1 so Y is 1 now is 1 less than
or equal to 20 that's true it comes here
1/2 the reminder is 1 so it comes here
so when this statement is encountered
continue what's going to happen as it's
not going going to continue from here it
will
skip the rest of the statement in the
for-loop go back here and start
executing again so it comes here
increments the value by one so I becomes
two now is two divided by two one Falls
so it prints two so every odd number is
now for every odd number this condition
will become true and when this condition
becomes true this continue keyword gets
executed when this continued keyword is
executed you know it will skip the rest
of the lines in the for loop go back
here and then starts again okay so if I
go ahead and run this it's going to
print even number it still is 20 so I
hope this has demonstrated the
significance of continue keyword if for
any reason you know in the for loop you
want to skip the instructions for a
specific condition you can have the
condition and use the continue keyword
alright so in this session we have seen
how to work with you know for loop and
foreach loop we have compared and
contrasted the differences between for
and while loop we have also seen how to
work with for each loop for each loops
helpers you know avoid index out of
range exceptions the difference between
four and 42 loop is that if you have to
use for loop you have to know how many
times you have to do whereas that's not
the case with for each loop and if
origin can be used with any type of
collection classes generates or arrays
we have also seen the significance of
break and continue keywords that's it
for today
thank you for listening have a great day