Part 6 - C# Tutorial - Nullable Types.avi Video Lecture | C sharp: Enhance your Skills (English) - Back-End Programming

hello welcome to prism technologies
I am anchored this is part six nullable
types in c-sharp
in this session we will learn nullable
types in C sharp and about null
coalescing or greater now actually in
c-sharp we can broadly divide the types
into two categories value types and
reference types in our previous module
we have already seen value types you
know the built-in value types like
integer
double low decimal etc okay and we also
have apart from these built-in value
types we also have reference types we
have seen one of the built-in reference
type widgets
string string is actually a class okay
an examples of reference types include
classes interface delegates arrays etc
we will talk about the differences
between value types and reference types
are in detail in a later session okay at
this point what we need to understand is
that in c-sharp the types can be divided
into two broad categories value types
and reference types examples of value
types in fluid etcetera examples for
value types classes interface delegates
etc and another point that we need to
keep in mind at this point is the
default value for reference types is now
whereas the default value for value
types is some form of zero for example
if it's an integer the default value for
any variable of type integer is zero and
they cannot hold null values let's
actually look at demo so for example I
told you a string which is a class is
actually a reference type so for example
when I say string name equals now and
then if we try to compile this it will
compile without any problem because
reference types can have null values but
whereas
by creative value type for example
integer is value type so into I equal to
now and if we try to look at this we
already have got the red squiggly cannot
convert null to an int because it's a
non nullable value type so i is a value
type and you cannot initialize that to a
null value okay but whereas reference
types can have null value so that's one
important difference at this point
between value types and reference types
there are several other major
differences between these two which we
will be talking about in a later session
okay now if i have to store a null value
in a value type how do i do that
is that at all possible in c-sharp
absolutely in c-sharp the value types
can be actually divided into two types
again non nullable value types and
nullable value types so if we go back to
the presentation so by default value
types are non malleable to make them
malleable use question mark so let me
give you an example for that so here i
is a non nullable integer datatype if i
have to make this nullable all i have to
do is use a question mark and now look
at that that red squiggly goes away
which means if you want to make a value
type nullable just put a question mark
next to the type that makes it nullable
datatype and why did GC shop introduce
this there are actually several reasons
one of the reasons is let's say for
example you have a form like this you
know where a user has to supply his
first name last name which are mandatory
but whereas i you a major this field is
optional and if the and the options for
this are s and now okay and in the as
this field is optional he might choose
not to answer if he says i mean if he
did the answer are you a major then how
will you store that value so let's say
for example we have a boolean flag here
boolean are you major in the application
now this can only be true or false
because look at this are you a major is
we don't have a question mark meaning
it's a non malleable value type okay so
if it's a non malleable value type and a
boolean value can only take true or
false but here if the user doesn't
select yes or no it means he didn't
select any answer for this field and
this field is optional so what value
will initialize this field wealth is it
true or false if you if you initialize
that with false it's as if the user has
said no okay so we should be in a
position to store null values in this
variable of type boolean because are you
a major yes no the user did not answer
there are three options actually if the
user didn't answer it means he did not
select any of the yes or no options for
this question so if he didn't select any
of the options then I should be capable
of storing null value otherwise we will
not be in a position to differentiate
between the user not answering the
question and saying no if we store this
value as false that's why this nullable
types are so much useful and another
reason why this malleable well nullable
types of Swee useful is because you know
databases does not have the concept of
value types of reference types whether
if it is n where care integer whatever
is the datatype you know you can store
null in the column of a table in a
database or any data type okay but value
types and reference types are only C
sharp concepts
okay so when it comes to working with
c-sharp and databases we have to have
you know some form of transformation
between nulls and non null value types
but with these nullable value types now
we don't have to do that conversion
anymore now it makes working with
database fields very much easy so these
are some of the reasons why these
nullable data types are very helpful in
c-sharp
so let's complete this example so I can
make this boolean are you major now so
within this form if the user does not
select yes or no options then this field
will be null anyways okay and let's say
for example we want to check if ru major
is equal to true we can say console dot
write line maybe user is major
you can either you know say are you
major is equal to true or you can simply
say are you major dot value from the
intellisense if you look at this this
value actually returns a boolean data
type not a nullable boolean data type
okay so you can say if it has to be
false so you can either say if this is
true user this major F not true user is
not major so you can either say it this
way or you can say it if are you major
is equal to false either of them will
work and yes okay keep in mind in a
label boolean data type can hold three
different values true false or now if it
is true you're saying user is major if
it's false user it's not major and if
it's not true and if it's not false the
only other option that's available it
could be now so we can just say
console.writeline user did not answer
the question
okay so now we are in a position you
know if the user didn't answer the
question here sno he didn't select any
of these options then are you major will
be now and we'll be in a position to say
user did not answer the question but in
case if we didn't have this boolean flag
we have we may have to initialize the to
false so in that case we would not have
been in a position to differentiate
between the user was dint answer the
question or is not major so now if we go
ahead and run since IU major this now we
get that user did not answer the
question
okay little grammatical mistake there
all right
on the other hand if he says true then
obviously user is major okay so that's
about nullable types you know even the
integer types you can make them nullable
okay all value types you know they have
they have the respect you count about
nullable types another concept that we
will talk about is the null coalescing
operator which is really interesting now
let's say for example I have a field
called you know number of tickets
tickets on sale equal to let's say 10
okay I have tickets on sale and I have
another variable let's call available
available tickets
say this tickets on sale is a nullable
datatype and there are no tickets on
sale right now which means tickets on
sale is now
so if tickets on sale is now then
obviously there are no tickets available
so if tickets on sale is equal to now
then we now available tickets we want to
initialize that to zero else
let's close this place else available
tickets equals whatever are the tickets
that are on sale and finally let's print
how many tickets are available so we can
say available tickets equals available
tickets now look at this we've got an
error here it's saying okay I cannot
implicitly convert type int question
mark to end meaning there is no implicit
conversion between an on nullable type
and an ala blue type okay we have to be
explicit about the conversion and one
way to do that is simply say dot value
dot value if you look at the
intellisense it returns and non Malibu
counterpart and int look at that end
without the question mark so that's one
way to do that or you can use the cast
operator we will talk about implicit and
explicit conversion in another session
in detail so you can either use this
conversion okay what we are doing is
okay this is a non 11 type if you look
at this tickets on sale let's say on
it's a nullable datatype but an end
without the question mark is a non
nullable datatype so we are for saying
non malleable datatype to be converted
sorry nullable datatype to be converted
into non malleable datatype and
assigning it to this variable okay so if
I go ahead and run this obviously since
tickets on sale is now available tickets
will be zero but on the other hand if
you initialize that to some number maybe
hundred tickets on sale obviously
available tickets will be hundred so
what's going to happen here it will
check ok tickets on sale these tickets
on sale now now it is equal to hundred
so it comes to the else block okay
tickets on sale value is 100 it will
convert that to non man double data type
integer and storage and stores it in
this variable and finally we print that
out okay now look at this if it is now
zero you know instead of null we are
initializing that great default value
because this cannot whole now this
variable because it's a non malleable
integer datatype okay now do we have to
have so many lines just to do that if it
is not now use the value that is present
and available in tickets on sale
otherwise use some default value so do
we really need to have these many lines
of code just to do that simple thing now
not really that's why we have this null
coalescing operator which we can make
use of and the way we do that is pretty
simple you can get rid of all these
lines and you can simply say in
available tickets is equal to tickets on
sale question mark question mark
that's your null coalescing operator and
whatever is the default value that you
want to initialize this variable where
in case if this nullable data type is
now okay so what does line is doing it's
pretty simple if tickets on sale is now
then use this default value otherwise
use the value that is present inside
this variable set simple s that's just
one line so if you go ahead and
and the behavior will be the same except
that instead of using if and else we are
using the Maluku lacing operator which
is very simple to use so this is without
an alkalizing operator and this is with
a local a single blade operator so you
can see the difference you know the
number of lines has been reduced so
that's it thank you for watching for
more resources you can refer to these
things on the slide have a good day bye
bye