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Small code review

Assuming the input to this program is

1
2
3
0
2
3
4
0

, is its behavior guaranteed to be well-defined? Is there anything
else about it that warrants comments and/or ridicule? The idea is to
accept two lists of numbers (separated by 0's) and print the numbers
that are in exactly one of the two lists; it seems to work.

#include <iostream>
#include <set>

int main()
{
unsigned int foo;
std::set< unsigned int > actual;
std::set< unsigned int > etb;
std::cin >> foo;
while( foo ) {
actual.insert( foo );
std::cin >> foo;
}
std::cin >> foo;
while( foo ) {
etb.insert( foo );
std::cin >> foo;
}
for( std::set<unsign ed int>::iterator i=actual.begin( ) ; i !=
actual.end() ; ) {
std::set<unsign ed int>::iterator j=etb.find( *i );
if( j != etb.end() ) {
std::set<unsign ed int>::iterator del=i;
++i;
actual.erase( del );
etb.erase( j );
}
else {
++i;
}
}
for( std::set<unsign ed int>::iterator i=actual.begin( ) ; i !=
actual.end() ; i++ ) {
std::cout << "actual: " << *i << std::endl;
}
for( std::set<unsign ed int>::iterator i=etb.begin() ; i !=
etb.end() ; i++ ) {
std::cout << "etb: " << *i << std::endl;
}
return 0;
}

--
Christopher Benson-Manica | I *should* know what I'm talking about - if I
ataru(at)cybers pace.org | don't, I need to know. Flames welcome.
Jul 22 '05 #1
2 1258
Christopher Benson-Manica wrote:
Assuming the input to this program is

1
2
3
0
2
3
4
0

, is its behavior guaranteed to be well-defined?
Methinks, yes.
Is there anything
else about it that warrants comments and/or ridicule?
See inline with code. Nothing to ridicule. Just two small things
I'd do differently.
The idea is to
accept two lists of numbers (separated by 0's) and print the numbers
that are in exactly one of the two lists; it seems to work.

#include <iostream>
#include <set>

int main()
{
unsigned int foo;
std::set< unsigned int > actual;
std::set< unsigned int > etb;
std::cin >> foo;
while( foo ) {
actual.insert( foo );
std::cin >> foo;
}
std::cin >> foo;
while( foo ) {
etb.insert( foo );
std::cin >> foo;
}
for( std::set<unsign ed int>::iterator i=actual.begin( ) ; i !=
actual.end() ; ) {
std::set<unsign ed int>::iterator j=etb.find( *i );
if( j != etb.end() ) {
std::set<unsign ed int>::iterator del=i;
++i;
You could easily do it in one statement:

std::set<unsign ed int>::iterator del = i++;
actual.erase( del );
etb.erase( j );
}
else {
++i;
}
I personally don't like extraneous curly braces. Personally.
}
for( std::set<unsign ed int>::iterator i=actual.begin( ) ; i !=
actual.end() ; i++ ) {
std::cout << "actual: " << *i << std::endl;
}
for( std::set<unsign ed int>::iterator i=etb.begin() ; i !=
etb.end() ; i++ ) {
std::cout << "etb: " << *i << std::endl;
}
return 0;
}


V
Jul 22 '05 #2

"Christophe r Benson-Manica" <at***@nospam.c yberspace.org> wrote in message
news:cl******** **@chessie.cirr .com...
Assuming the input to this program is

1
2
3
0
2
3
4
0

, is its behavior guaranteed to be well-defined? Is there anything
else about it that warrants comments and/or ridicule? The idea is to
accept two lists of numbers (separated by 0's) and print the numbers
that are in exactly one of the two lists; it seems to work.

#include <iostream>
#include <set>

int main()
{
unsigned int foo;
std::set< unsigned int > actual;
std::set< unsigned int > etb;
std::cin >> foo;
while( foo ) {
actual.insert( foo );
std::cin >> foo;
}
std::cin >> foo;
while( foo ) {
etb.insert( foo );
std::cin >> foo;
}
for( std::set<unsign ed int>::iterator i=actual.begin( ) ; i !=
actual.end() ; ) {
std::set<unsign ed int>::iterator j=etb.find( *i );
if( j != etb.end() ) {
std::set<unsign ed int>::iterator del=i;
++i;
actual.erase( del );
etb.erase( j );
}
else {
++i;
}
}
for( std::set<unsign ed int>::iterator i=actual.begin( ) ; i !=
actual.end() ; i++ ) {
std::cout << "actual: " << *i << std::endl;
}
for( std::set<unsign ed int>::iterator i=etb.begin() ; i !=
etb.end() ; i++ ) {
std::cout << "etb: " << *i << std::endl;
}

This is one of the occasions when the STL really does work. The above three
loops could be written as a couple of lines

std::ostream_it erator<unsigned int> output(std::cou t, "\n");
std::set_symmet ric_difference( actual.begin( ), actual.end( ), etb.begin( ),
etb.end( ), output);

You would lose the output "actual: " and "etb: " but if you were worried
about that then try this

std::ostream_it erator<unsigned int> output(std::cou t, "\n");
std::cout << "actual: ";
std::set_differ ence(actual.beg in(), actual.end(), etb.begin(), etb.end(),
output);
std::cout << "etb: ";
std::set_differ ence(etb.begin( ), etb.end(), actual.begin(), actual.end(),
output);

That's pretty close to what you had.

john
Jul 22 '05 #3

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