Part 44 C# Tutorial Preventing exception handling abuse Video Lecture -

hello welcome to prism technologies I'm
Lincoln this is part 4 t4 exception
handling abused SOG in part 43 we have
seen a classic example of exception
handling abuse in this session we will
see how to prevent that ok so we will
jump straight back in to the example if
you haven't watched part 43 I would
strongly encourage you to do so before
continuing with this example all right
just a quick recap on what we have seen
in the previous example we ask the user
to enter a numerator we ask the user to
enter a denominator and when he enters a
numerator they are actually reading it
from the console and trying to convert
that integer and we know that if the
user enters alphabets instead of numbers
it's gonna through a format exception
and in the catch block basically we are
saying please enter a number and
similarly if he enters a very big number
again there will be an overflow
exception then we try to convert that to
an integer
again we catch that exception and then
we say ok the number should only be
between the minimum and maximum value
that an integer type can hold and
similarly you know if the denominator is
zero it tries to divide that and we get
it divided by zero exception and we
catch that exception and then we tell
the user so basically you are allow this
program to through the respective
exceptions and then you are using that
exception handling basically to control
what error messages to be shown to the
user and subsequently the flow program
which is definitely exception handling
abuse now we can actually rewrite this
program and without even having these
exceptions occurring we can present user
with those respect to messages ok now
let's see how to rewrite this program so
obviously as usual we'll pass the user
to enter a numerator now instead of
using the converter to int32 method
which will throw an exception if the
conversion fails within dotnet framework
we also have tryparse method which we
can use so the way we do it is actually
let's say int numerator
and then if you look at the try bars
method so it's again on integer in 32 or
try parts if you look at the signature
of this method what is this method doing
it's gonna return a boolean a true or
false so if the conversion is successful
it will return true otherwise it returns
false and if you look at the parameter
is that this method takes in there is a
string parameter so obviously the number
I mean whatever the user input that the
user has entered so that string and then
you have to pass in an output parameter
now if you're new to output parameters I
would strongly encourage you to watch
you know a video tutorial on method
parameters in the series all right so to
read the input from the comes will be
used consult riedel read line and we
pass that as the first parameter so
obviously whatever the user has entered
to read that and pass to this tryparse
method
now this tryparse method what it does it
will convert that to an integer if
possible and returns that in this output
parameters out and then we pass the
variable here which will receive the
converted value so if the conversion is
successful if this method can really
successfully converted that input to an
integer then it will store that in this
variable ok so now what we need to do
since this method returns a boolean a
true or false okay so we will declare a
variable of type boolean okay is
numerator conversion successful just a
variable to determine if the conversion
is successful okay so if
is numerator conversion as successful in
the sense if it has successfully
converted that then we know that there
is no problem and we can continue to ask
the user for denominator so we will do
all this only if the numerator
conversion is successful so the next
thing that we will do is basically ask
the user to enter a denominator and
obviously just like for the numerator I
will copy paste this so we'll create a
variable which can receive the
denominator value and we can get rid of
this line and we will call this variable
E's denominator conversion successful
and then what we do we read the user in
that he has entered and the converted
value store within this parameter
variable denominator
okay so we have denominator as well
right now so what you need to do here is
similarly if he's denominator conversion
is successful and at the same time it
cannot be 0 it shouldn't be zero because
if the denominator is zero you know the
program will through divide by zero
exception and each denominator not equal
to zero
then what we do we will go ahead and
safely calculate the result and print
the output to the user okay if E's
denominator conversion conversion
successful and denominator not equal to
zero right
okay on the other hand if is numerator
conversion is not successful then what
we want to do we want to give a
meaningful error message to the user
console dot readline so obviously we
know that numerator conversion is not
successful
why because either he entered you know
alphabets or the entered value is beyond
you know what an integer variable can
hold so what you can do is you can
actually put a very meaningful message
saying that numerator should be a valid
number between whatever is the minimum
and maximum value that an integer type
can hold so obviously what we can do
here is in 32 dot min value and in turn
32 dot Max value all right
similarly if each denominator is
successful and denominator not equal to
0 okay calculate the result and display
the result else
if you know denominator you know it will
come into the else block if either of
these conditions is false so if
denominator is equal to zero we know
that a denominator cannot be zero else
we know that the denominator conversion
has failed so if the denominator
conversion has failed then we want to
say the the user okay
denominator should be a valid number so
denominator
be a valid number between you know the
minimum and maximum value on the other
hand if denominator is equal to zero we
can say denominator cannot be zero so
copy that and put it in the safe block
okay now if you look at this we are not
allowing you know
exceptions to occur instead we are
programmatically checking okay all the
values what we expect we are validating
the user input similarly you're saying
you know the conversion is successful or
not and based on that you are
controlling what we want to display to
the user and and we are in turn
controlling the program logical flow so
after this modification what you can
basically do is actually get rid of all
these exceptions because there's no
possibility for these to occur and we
can just leave the general exception
block here just in case if there is any
other exception that we didn't
anticipate and if there is a chance of
that happening you know we can basically
handle that there but now if you run
this the behavior is going to be almost
identical to what we have seen in for in
part 43 but now this is a better way of
programming so now if I enter alphabets
instead of numbers so numerator should
be a valid number similarly if I enter a
very big number which an integer cannot
call you know obviously the conversion
will fail and we get the same error and
similarly if you know I'm enter a valid
numerator and if I enter 0 for the
denominator denominator cannot be zero
so it's doing all the validations it
should be doing in the right way but the
difference between how we have written
program now and in part 43 is that in
part 43 we were using exception handling
basically to control the logical flow
but in this part we are using
programming techniques you know and we
are avoiding the exceptions from
unnecessarily happening so using
exception handling to implement program
logical flow is bad and that is what is
termed as exception handling
abuse and we have seen how to prevent
that with good programming practices for
example using tryparse method instead of
convert
third convert method will allow the
exception to happen whereas tryparse
will return a true or false depending on
the success or failure of the conversion
I hope you have enjoyed this session on
this slide you can see C sharp and a
speed interview questions that's it for
today thank you for listening have a
great day