It works fine. any advice on making it better or if I can
improve my C++ coding skills:
/* C++ Primer - 4/e
*
* Chapter 9 - Sequential Containers
* exercise 9.18 - STATEMENT
* Write a program to copy elements from a list of "ints"
* to 2 "deques". The list elements that are even should go into one deque
* and even elements should go into 2nd deque.
*
*/
#include <iostream>
#include <list>
#include <deque>
#include <algorithm>
#include <iterator>
int main()
{
std::cout << "enter some integers: ";
std::list<intil ist;
/* copy elements from std::cin into ilist */
std::copy( (std::istream_i terator<int>( std::cin )),
(std::istream_i terator<int>()) ,
std::back_inser ter( ilist ) );
std::deque<intd eque_of_evens;
std::deque<intd eque_of_odds;
/* copy even elements into 1 deque and odds into the other */
for( std::list<int>: :const_iterator iter = ilist.begin();
iter != ilist.end();
++iter)
{
if( *iter % 2 == 0 )
{
deque_of_evens. push_back( *iter );
}
else
{
deque_of_odds.p ush_back( *iter );
}
}
std::cout << "\n Printing Deque of Even Integers: ";
std::copy( deque_of_evens. begin(),
deque_of_evens. end(),
std::ostream_it erator<int>( std::cout, " " ) );
std::cout << "\n\n Printing Deque of Odd Integers: ";
std::copy( deque_of_odds.b egin(),
deque_of_odds.e nd(),
std::ostream_it erator<int>( std::cout, " " ) );
std::cout << std::endl;
return 0;
}
-- http://lispmachine.wordpress.com 12  2650 
On 2007-09-25 09:59, arnuld wrote:
It works fine. any advice on making it better or if I can
improve my C++ coding skills:
/* C++ Primer - 4/e
*
* Chapter 9 - Sequential Containers
* exercise 9.18 - STATEMENT
* Write a program to copy elements from a list of "ints"
* to 2 "deques". The list elements that are even should go into one deque
* and even elements should go into 2nd deque.
*
*/
#include <iostream>
#include <list>
#include <deque>
#include <algorithm>
#include <iterator>
int main()
{
std::cout << "enter some integers: ";
std::list<intil ist;
/* copy elements from std::cin into ilist */
std::copy( (std::istream_i terator<int>( std::cin )),
(std::istream_i terator<int>()) ,
std::back_inser ter( ilist ) );
std::deque<intd eque_of_evens;
std::deque<intd eque_of_odds;
/* copy even elements into 1 deque and odds into the other */
for( std::list<int>: :const_iterator iter = ilist.begin();
iter != ilist.end();
++iter)
{
if( *iter % 2 == 0 )
{
deque_of_evens. push_back( *iter );
}
else
{
deque_of_odds.p ush_back( *iter );
}
}
std::cout << "\n Printing Deque of Even Integers: ";
std::copy( deque_of_evens. begin(),
deque_of_evens. end(),
std::ostream_it erator<int>( std::cout, " " ) );
std::cout << "\n\n Printing Deque of Odd Integers: ";
std::copy( deque_of_odds.b egin(),
deque_of_odds.e nd(),
std::ostream_it erator<int>( std::cout, " " ) );
std::cout << std::endl;
return 0;
}
You should research the (IMO badly named) remove_copy_if algorithm and
create a predicate to determine if the element is even or not.
--
Erik Wikström
Erik Wikström wrote:
On 2007-09-25 09:59, arnuld wrote:
>It works fine. any advice on making it better or if I can
improve my C++ coding skills:
/* C++ Primer - 4/e
*
* Chapter 9 - Sequential Containers
* exercise 9.18 - STATEMENT
* Write a program to copy elements from a list of
"ints" * to 2 "deques". The list elements that are even should go into
one deque * and even elements should go into 2nd deque.
*
*/
#include <iostream>
#include <list>
#include <deque>
#include <algorithm>
#include <iterator>
int main()
{
std::cout << "enter some integers: ";
std::list<intil ist;
/* copy elements from std::cin into ilist */
std::copy( (std::istream_i terator<int>( std::cin )),
(std::istream_ iterator<int>() ),
std::back_inse rter( ilist ) );
std::deque<intd eque_of_evens;
std::deque<intd eque_of_odds;
/* copy even elements into 1 deque and odds into the other */
for( std::list<int>: :const_iterator iter = ilist.begin();
iter != ilist.end();
++iter)
{
if( *iter % 2 == 0 )
{
deque_of_evens .push_back( *iter );
}
else
{
deque_of_odds. push_back( *iter );
}
}
std::cout << "\n Printing Deque of Even Integers: ";
std::copy( deque_of_evens. begin(),
deque_of_evens .end(),
std::ostream_i terator<int>( std::cout, " " ) );
std::cout << "\n\n Printing Deque of Odd Integers: ";
std::copy( deque_of_odds.b egin(),
deque_of_odds. end(),
std::ostream_i terator<int>( std::cout, " " ) );
std::cout << std::endl;
return 0;
}
You should research the (IMO badly named) remove_copy_if algorithm and
create a predicate to determine if the element is even or not.
And: you should implement the missing (sic!) copy_if algorithm and use the
same predicate for the other copy job.
Best
Kai-Uwe Bux
On Sep 25, 11:24 am, Kai-Uwe Bux <jkherci...@gmx .netwrote:
Erik Wikström wrote:
On 2007-09-25 09:59, arnuld wrote:
It works fine. any advice on making it better or if I can
improve my C++ coding skills:
/* C++ Primer - 4/e
*
* Chapter 9 - Sequential Containers
* exercise 9.18 - STATEMENT
* Write a program to copy elements from a list of
"ints" * to 2 "deques". The list elements that are even should go into
one deque * and even elements should go into 2nd deque.
*
*/
#include <iostream>
#include <list>
#include <deque>
#include <algorithm>
#include <iterator>
int main()
{
std::cout << "enter some integers: ";
std::list<intil ist;
/* copy elements from std::cin into ilist */
std::copy( (std::istream_i terator<int>( std::cin )),
(std::istream_i terator<int>()) ,
std::back_inser ter( ilist ) );
std::deque<intd eque_of_evens;
std::deque<intd eque_of_odds;
/* copy even elements into 1 deque and odds into the other */
for( std::list<int>: :const_iterator iter = ilist.begin();
iter != ilist.end();
++iter)
{
if( *iter % 2 == 0 )
{
deque_of_evens. push_back( *iter );
}
else
{
deque_of_odds.p ush_back( *iter );
}
You might replace the if with:
(*iter % 2 == 0 ? deque_of_evens :
deque_of_odds). push_back( *iter ) ;
Opinions about this vary; I tend not to use ?: very much for
lvalues, but in this case, it does draw attention to the fact
that *all* of the elements end up in one of the two deques.
}
std::cout << "\n Printing Deque of Even Integers: ";
std::copy( deque_of_evens. begin(),
deque_of_evens. end(),
std::ostream_it erator<int>( std::cout, " " ) );
std::cout << "\n\n Printing Deque of Odd Integers: ";
std::copy( deque_of_odds.b egin(),
deque_of_odds.e nd(),
std::ostream_it erator<int>( std::cout, " " ) );
std::cout << std::endl;
return 0;
}
You should research the (IMO badly named) remove_copy_if
algorithm and create a predicate to determine if the element
is even or not.
And: you should implement the missing (sic!) copy_if algorithm
and use the same predicate for the other copy job.
I'm not sure that I agree with either of these recommendations .
Both smack of obfuscation, and forcing things just to use a
standard (or non-standard, in the case of copy_if) algorithm.
For a more experienced programmer, I might consider a
boost::filter_i terator, e.g.:
std::deque< int evens(
boost::make_fil ter_iterator< IsEven >( ilist.begin(),
ilist.end() ),
boost::make_fil ter_iterator< IsEven >( ilist.end(),
ilist.end() ) ) ;
std::deque< int odds(
boost::make_fil ter_iterator< IsOdd >( ilist.begin(),
ilist.end() ),
boost::make_fil ter_iterator< IsOdd >( ilist.end(),
ilist.end() ) ) ;
This allows correct initialization; it would even allow making
evens and odds const. But it still requires moving the test out
of the loop, and even out of the function. And I'm pretty sure
that it's not the intent of the exercise.
--
James Kanze (GABI Software) email:ja******* **@gmail.com
Conseils en informatique orientée objet/
Beratung in objektorientier ter Datenverarbeitu ng
9 place Sémard, 78210 St.-Cyr-l'École, France, +33 (0)1 30 23 00 34
On Sep 25, 2:56 pm, James Kanze <james.ka...@gm ail.comwrote:
You might replace the if with:
(*iter % 2 == 0 ? deque_of_evens :
deque_of_odds). push_back( *iter ) ;
Opinions about this vary; I tend not to use ?: very much for
lvalues, but in this case, it does draw attention to the fact
that *all* of the elements end up in one of the two deques.
that's nice James (as for as my exercise is concerned ). I have
used that construct, it make my solution look clean :-)
James Kanze wrote:
On Sep 25, 11:24 am, Kai-Uwe Bux <jkherci...@gmx .netwrote:
>Erik Wikström wrote:
On 2007-09-25 09:59, arnuld wrote:
It works fine. any advice on making it better or if I can
improve my C++ coding skills:
>/* C++ Primer - 4/e
*
* Chapter 9 - Sequential Containers
* exercise 9.18 - STATEMENT
* Write a program to copy elements from a list of
"ints" * to 2 "deques". The list elements that are even should go
into one deque * and even elements should go into 2nd deque.
*
*/
>#include <iostream>
#include <list>
#include <deque>
#include <algorithm>
#include <iterator>
>int main()
{
std::cout << "enter some integers: ";
std::list<intil ist;
/* copy elements from std::cin into ilist */
std::copy( (std::istream_i terator<int>( std::cin )),
(std::istream_ iterator<int>() ),
std::back_inse rter( ilist ) );
> std::deque<intd eque_of_evens;
std::deque<intd eque_of_odds;
/* copy even elements into 1 deque and odds into the other */
for( std::list<int>: :const_iterator iter = ilist.begin();
iter != ilist.end();
++iter)
{
if( *iter % 2 == 0 )
{
deque_of_evens .push_back( *iter );
}
else
{
deque_of_odds. push_back( *iter );
}
You might replace the if with:
(*iter % 2 == 0 ? deque_of_evens :
deque_of_odds). push_back( *iter ) ;
Opinions about this vary; I tend not to use ?: very much for
lvalues, but in this case, it does draw attention to the fact
that *all* of the elements end up in one of the two deques.
> }
> std::cout << "\n Printing Deque of Even Integers: ";
std::copy( deque_of_evens. begin(),
deque_of_evens .end(),
std::ostream_i terator<int>( std::cout, " " ) );
> std::cout << "\n\n Printing Deque of Odd Integers: ";
std::copy( deque_of_odds.b egin(),
deque_of_odds. end(),
std::ostream_i terator<int>( std::cout, " " ) );
> std::cout << std::endl;
return 0;
}
You should research the (IMO badly named) remove_copy_if
algorithm and create a predicate to determine if the element
is even or not.
>And: you should implement the missing (sic!) copy_if algorithm
and use the same predicate for the other copy job.
I'm not sure that I agree with either of these recommendations .
Both smack of obfuscation, and forcing things just to use a
standard (or non-standard, in the case of copy_if) algorithm.
I have a great deal of sympathy for that sentiment. Functors tend to move
code from the place where you would like to see it to some other place.
That is generally not so good.
For a more experienced programmer, I might consider a
boost::filter_i terator, e.g.:
std::deque< int evens(
boost::make_fil ter_iterator< IsEven >( ilist.begin(),
ilist.end() ),
boost::make_fil ter_iterator< IsEven >( ilist.end(),
ilist.end() ) ) ;
std::deque< int odds(
boost::make_fil ter_iterator< IsOdd >( ilist.begin(),
ilist.end() ),
boost::make_fil ter_iterator< IsOdd >( ilist.end(),
ilist.end() ) ) ;
This allows correct initialization; it would even allow making
evens and odds const. But it still requires moving the test out
of the loop, and even out of the function.
[snip]
In a case like this, I like lambda:
std::remove_cop y_if( ilist.begin(), ilist.end(),
std::back_inser ter( deque_of_evens ),
_1 % 2 != 0 );
std::remove_cop y_if( ilist.begin(), ilist.end(),
std::back_inser ter( deque_of_odds ),
_1 % 2 == 0 );
(yet, I would prefer copy_if :-)
I agree, though, that cases where lambda is this concise are rare. But
compared to using std::binder..., std::modulus, ... lambda is great.
Best
Kai-Uwe Bux
On Sep 25, 3:23 pm, Kai-Uwe Bux <jkherci...@gmx .netwrote:
In a case like this, I like lambda:
std::remove_cop y_if( ilist.begin(), ilist.end(),
std::back_inser ter( deque_of_evens ),
_1 % 2 != 0 );
std::remove_cop y_if( ilist.begin(), ilist.end(),
std::back_inser ter( deque_of_odds ),
_1 % 2 == 0 );
ok, that's nice :)
and i did not get that _1 %2, I know it checks for even and odd
numbers but what exactly that "underscore 1" means: _1 %2
arnuld wrote:
>On Sep 25, 3:23 pm, Kai-Uwe Bux <jkherci...@gmx .netwrote:
>In a case like this, I like lambda:
std::remove_cop y_if( ilist.begin(), ilist.end(),
std::back_inser ter( deque_of_evens ),
_1 % 2 != 0 );
std::remove_cop y_if( ilist.begin(), ilist.end(),
std::back_inser ter( deque_of_odds ),
_1 % 2 == 0 );
ok, that's nice :)
and i did not get that _1 %2, I know it checks for even and odd
numbers but what exactly that "underscore 1" means: _1 %2
That's the magic of expression templates. If you are interested, you can
have a look at my posting http://groups.google.com/group/comp....422ea883a2b151
where I explain how one can about implementing something like that. Be
warned, however: it takes about 600 lines of code (and 300 lines of
comments) to make that _1 work (and that is just a proof of concept!).
Luckily, it already has been done and is in boost.
Best
Kai-Uwe Bux
On Sep 25, 2:56 pm, James Kanze <james.ka...@gm ail.comwrote:
I'm not sure that I agree with either of these recommendations .
Both smack of obfuscation, and forcing things just to use a
standard (or non-standard, in the case of copy_if) algorithm.
For a more experienced programmer, I might consider a
boost::filter_i terator, e.g.:
std::deque< int evens(
boost::make_fil ter_iterator< IsEven >( ilist.begin(),
ilist.end() ),
boost::make_fil ter_iterator< IsEven >( ilist.end(),
ilist.end() ) ) ;
std::deque< int odds(
boost::make_fil ter_iterator< IsOdd >( ilist.begin(),
ilist.end() ),
boost::make_fil ter_iterator< IsOdd >( ilist.end(),
ilist.end() ) ) ;
This allows correct initialization; it would even allow making
evens and odds const. But it still requires moving the test out
of the loop, and even out of the function. And I'm pretty sure
that it's not the intent of the exercise.
I am trying this but can not copile my program with that without
errors. I am using remove_copy_if as suggested by Kai-Uwe Bux
(remember the _1 ;-)
but still I am interested in this use of boost library. I have copied
the code you wrote but then I am not able to get what to do to
make use of this make_filter_ite rator.
any explanation ?
On Sep 25, 12:23 pm, Kai-Uwe Bux <jkherci...@gmx .netwrote:
James Kanze wrote:
[...]
And: you should implement the missing (sic!) copy_if algorithm
and use the same predicate for the other copy job.
I'm not sure that I agree with either of these recommendations .
Both smack of obfuscation, and forcing things just to use a
standard (or non-standard, in the case of copy_if) algorithm.
I have a great deal of sympathy for that sentiment. Functors
tend to move code from the place where you would like to see
it to some other place. That is generally not so good.
It depends. If you can supply a good, explicit name for the
function, and it is a "pure" function, not depending on any
local variables, it's not that bad. If you can reasonably
expect to use the function elsewhere, it's even good. I'd say
that his case meets the first criteron, but not really the
second. So it's not too bad, but I still prefer the test in an
explicit loop. (There's also the question of how much you're
throwing at the OP at a time. He IS working his way through a
tutorial text, and shouldn't be expected to handle everything at
once. Each thing in its time.)
For a more experienced programmer, I might consider a
boost::filter_i terator, e.g.:
std::deque< int evens(
boost::make_fil ter_iterator< IsEven >( ilist.begin(),
ilist.end() ),
boost::make_fil ter_iterator< IsEven >( ilist.end(),
ilist.end() ) ) ;
std::deque< int odds(
boost::make_fil ter_iterator< IsOdd >( ilist.begin(),
ilist.end() ),
boost::make_fil ter_iterator< IsOdd >( ilist.end(),
ilist.end() ) ) ;
This allows correct initialization; it would even allow
making evens and odds const. But it still requires moving
the test out of the loop, and even out of the function.
[snip]
In a case like this, I like lambda:
std::remove_cop y_if( ilist.begin(), ilist.end(),
std::back_inser ter( deque_of_evens ),
_1 % 2 != 0 );
std::remove_cop y_if( ilist.begin(), ilist.end(),
std::back_inser ter( deque_of_odds ),
_1 % 2 == 0 );
(yet, I would prefer copy_if :-)
I agree, though, that cases where lambda is this concise are
rare. But compared to using std::binder..., std::modulus, ...
lambda is great.
If we had a real lambda, it would be great (although as you
point out, in this particular case, boost::lambda works like a
real lambda). Ideally, even, we'd have a lambda which resolved
to a class which could be used to instantiate a template like
boost::make_fil ter_iterator, so I could replace IsEven and IsOdd
in my example.
--
James Kanze (GABI Software) email:ja******* **@gmail.com
Conseils en informatique orientée objet/
Beratung in objektorientier ter Datenverarbeitu ng
9 place Sémard, 78210 St.-Cyr-l'École, France, +33 (0)1 30 23 00 34 This thread has been closed and replies have been disabled. Please start a new discussion. Similar topics | |
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