Conditional Compilation Macros ifdef ifndef undef in C Video Tutorial Video

this is Anil with a video tutorial for
the learning guide on C programming in
this video tutorial we can see the
conditional compilation statements like
if live and if end if then we're going
to see the undef directive in see the
syntax of this if diff directive is here
so as you can see if this macro name is
defined by using hash defined directive
then these statements will be added by
the preprocessor in our expanded source
code so that you know the compiler is
going to compile that code so if this
macro name is not defined by using has
defined directive then this statement
will not be added or included by our
preprocessor and in the expanded source
code you know these statements will not
be there so this statement will not be
compiled by our compiler so the syntax
of this if end if is is this one here
just the compliment of the if div so if
this macro name is not defined by using
has defined directive then this
statement will be added or included by
our preprocessor in the expanded source
code and so that our compiler is going
to compile that statements so it just a
complement of this if div and the next
thing is this unde if we use this and if
to undefined any anemic rows which are
defined by using hash define and
directive so we're going to see about
that later first we are going to begin
with this if div now for the
demonstration purpose we're going to
define a macro by using task define and
we're going to name it as okay Intel
so now in our main main function you're
going to check whether if this macro is
defined so it's going to be hash if live
Intel has a macro name then we want to
execute some code within this if live
and ended so here when you want to print
something let's say goes for the Intel
PC save it compile it and run so as you
can see here since this Intel macro is
defined by using this hash defined here
you know the core for the Intel PC will
be included by our preprocessor in our
expanded source code you know that's why
our compiler is going to compile that
that statement now we're going to close
it so now for the demonstration purpose
we're going to remove this line save it
compile it and run it so as you can see
here nothing is printed that's because
this if dip resulted in false or this
Intel macro name is not defined that's
why this printf statement is skipped so
now we can use this if not defined now
this Intel macro is not defined in our
program using hash define that's why
this printf statement will be included
actually this Intel macro is not defined
that's why it's going to be for the non
Intel PC so as you can see the co for
the non Intel PC and now we're going to
define it this can be hash define
Intel's now in term acronym is define
now we can use this hash undoped to
undefined this macro so now save it
compile it and run it so as you can see
here since this Intel macro is defined
you know this printf statement is
skipped now we are going to close
it and we're going to use this has undef
and undefined this Intel
macro name now save it now what happens
is first we are defining this Intel
macro and then we are undefined in it
so when it comes to here if and if Intel
here you know this Intel macro is not
defined that's because you know we have
undefined it that's why this printf
statement will be included so save it
compile it and run it so as you can see
here go for the non Intel PC so this is
it this is about the if you'd if if end
if and and if so thanks for watching and
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