different result from (using namespace std; cin …) vs (std::cin)
$begingroup$
While working on this online judge problem, I encountered a strange behavior: the below code, intended to read, line-by-line, 5-tuples of numbers representing points (x1,y1), (x2,y2) and p for a p-norm, and output their distance, was judged wrong:
#include <bits/stdc++.h>
int main()
{
float x1,y1,x2,y2,p,res;
while (std::cin>>x1>>y1>>x2>>y2>>p) {
res = pow( pow( abs(x1-x2) ,p) + pow( abs(y1-y2) ,p) ,(1/p));
printf("%.10fn",res);
}
return 0;
}
whereas the barely different code:
#include <bits/stdc++.h>
using namespace std;
int main()
{
float x1,y1,x2,y2,p,res;
while (cin>>x1>>y1>>x2>>y2>>p) {
res = pow( pow( abs(x1-x2) ,p) + pow( abs(y1-y2) ,p) ,(1/p));
printf("%.10fn",res);
}
return 0;
}
WAS judged correct. All I changed from one to the other was using the namespace std, and substituting cin by std::cin. My understanding was that "using namespace std" here means the compiler interprets all occurrences of "cout" as "std::cout" but I guess something subtler is going on. The reason I'm interested is that I was advised to avoid using namespaces to improve readability in the future when working with multiple files -- however doing so here mysteriously appears to be wrong.
c++ beginner
asked 4 hours ago
user191196user191196
97
New contributor
user191196 is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
$endgroup$
|
show 1 more comment
$begingroup$
While working on this online judge problem, I encountered a strange behavior: the below code, intended to read, line-by-line, 5-tuples of numbers representing points (x1,y1), (x2,y2) and p for a p-norm, and output their distance, was judged wrong:
#include <bits/stdc++.h>
int main()
{
float x1,y1,x2,y2,p,res;
while (std::cin>>x1>>y1>>x2>>y2>>p) {
res = pow( pow( abs(x1-x2) ,p) + pow( abs(y1-y2) ,p) ,(1/p));
printf("%.10fn",res);
}
return 0;
}
whereas the barely different code:
#include <bits/stdc++.h>
using namespace std;
int main()
{
float x1,y1,x2,y2,p,res;
while (cin>>x1>>y1>>x2>>y2>>p) {
res = pow( pow( abs(x1-x2) ,p) + pow( abs(y1-y2) ,p) ,(1/p));
printf("%.10fn",res);
}
return 0;
}
WAS judged correct. All I changed from one to the other was using the namespace std, and substituting cin by std::cin. My understanding was that "using namespace std" here means the compiler interprets all occurrences of "cout" as "std::cout" but I guess something subtler is going on. The reason I'm interested is that I was advised to avoid using namespaces to improve readability in the future when working with multiple files -- however doing so here mysteriously appears to be wrong.
c++ beginner
asked 4 hours ago
user191196user191196
97
New contributor
user191196 is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
$endgroup$
$begingroup$
I don't have access to test cases from Kattis; however the best I can offer in terms of replication is to ask you to submit both versions at the Kattis link in the post; the "wrong" one fails test case 2
$endgroup$
– user191196
4 hours ago
2
$begingroup$
Sorry, but this is off-topic here. This site is for working code only. The online judge seems to be the problem since the only difference isusing namespace std. Your best bet is to contact kattis. If you want this to be on-topic here, you can edit your question to ask how to improve either one of the two versions.
$endgroup$
– Null
4 hours ago
1
$begingroup$
The use of a non-standard include filebits/stdc++.his not good practice.
$endgroup$
– Edward
4 hours ago
$begingroup$
@Null it seems that you're saying there should be no difference -- which is exactly what I'm calling into question. If they are the same thing, why the side effects. and I will stop using bits, thanks. I wonder if that is causing some sort of clash.
$endgroup$
– user191196
4 hours ago
$begingroup$
Without the test cases we can't really say what the problem is. You could try to prefix all calls topow()andabs()withstd::as they are in the standard namespace, too.
$endgroup$
– Null
3 hours ago
|
show 1 more comment
$begingroup$
While working on this online judge problem, I encountered a strange behavior: the below code, intended to read, line-by-line, 5-tuples of numbers representing points (x1,y1), (x2,y2) and p for a p-norm, and output their distance, was judged wrong:
#include <bits/stdc++.h>
int main()
{
float x1,y1,x2,y2,p,res;
while (std::cin>>x1>>y1>>x2>>y2>>p) {
res = pow( pow( abs(x1-x2) ,p) + pow( abs(y1-y2) ,p) ,(1/p));
printf("%.10fn",res);
}
return 0;
}
whereas the barely different code:
#include <bits/stdc++.h>
using namespace std;
int main()
{
float x1,y1,x2,y2,p,res;
while (cin>>x1>>y1>>x2>>y2>>p) {
res = pow( pow( abs(x1-x2) ,p) + pow( abs(y1-y2) ,p) ,(1/p));
printf("%.10fn",res);
}
return 0;
}
WAS judged correct. All I changed from one to the other was using the namespace std, and substituting cin by std::cin. My understanding was that "using namespace std" here means the compiler interprets all occurrences of "cout" as "std::cout" but I guess something subtler is going on. The reason I'm interested is that I was advised to avoid using namespaces to improve readability in the future when working with multiple files -- however doing so here mysteriously appears to be wrong.
c++ beginner
asked 4 hours ago
user191196user191196
97
New contributor
user191196 is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
$endgroup$
While working on this online judge problem, I encountered a strange behavior: the below code, intended to read, line-by-line, 5-tuples of numbers representing points (x1,y1), (x2,y2) and p for a p-norm, and output their distance, was judged wrong:
#include <bits/stdc++.h>
int main()
{
float x1,y1,x2,y2,p,res;
while (std::cin>>x1>>y1>>x2>>y2>>p) {
res = pow( pow( abs(x1-x2) ,p) + pow( abs(y1-y2) ,p) ,(1/p));
printf("%.10fn",res);
}
return 0;
}
whereas the barely different code:
#include <bits/stdc++.h>
using namespace std;
int main()
{
float x1,y1,x2,y2,p,res;
while (cin>>x1>>y1>>x2>>y2>>p) {
res = pow( pow( abs(x1-x2) ,p) + pow( abs(y1-y2) ,p) ,(1/p));
printf("%.10fn",res);
}
return 0;
}
WAS judged correct. All I changed from one to the other was using the namespace std, and substituting cin by std::cin. My understanding was that "using namespace std" here means the compiler interprets all occurrences of "cout" as "std::cout" but I guess something subtler is going on. The reason I'm interested is that I was advised to avoid using namespaces to improve readability in the future when working with multiple files -- however doing so here mysteriously appears to be wrong.
c++ beginner
c++ beginner
asked 4 hours ago
user191196user191196
97
New contributor
user191196 is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
asked 4 hours ago
user191196user191196
97
New contributor
user191196 is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
asked 4 hours ago
user191196user191196
97
New contributor
user191196 is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
asked 4 hours ago
user191196user191196
97
asked 4 hours ago
user191196user191196
97
97
New contributor
user191196 is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
New contributor
user191196 is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
user191196 is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
$begingroup$
I don't have access to test cases from Kattis; however the best I can offer in terms of replication is to ask you to submit both versions at the Kattis link in the post; the "wrong" one fails test case 2
$endgroup$
– user191196
4 hours ago
2
$begingroup$
Sorry, but this is off-topic here. This site is for working code only. The online judge seems to be the problem since the only difference isusing namespace std. Your best bet is to contact kattis. If you want this to be on-topic here, you can edit your question to ask how to improve either one of the two versions.
$endgroup$
– Null
4 hours ago
1
$begingroup$
The use of a non-standard include filebits/stdc++.his not good practice.
$endgroup$
– Edward
4 hours ago
$begingroup$
@Null it seems that you're saying there should be no difference -- which is exactly what I'm calling into question. If they are the same thing, why the side effects. and I will stop using bits, thanks. I wonder if that is causing some sort of clash.
$endgroup$
– user191196
4 hours ago
$begingroup$
Without the test cases we can't really say what the problem is. You could try to prefix all calls topow()andabs()withstd::as they are in the standard namespace, too.
$endgroup$
– Null
3 hours ago
|
show 1 more comment
$begingroup$
I don't have access to test cases from Kattis; however the best I can offer in terms of replication is to ask you to submit both versions at the Kattis link in the post; the "wrong" one fails test case 2
$endgroup$
– user191196
4 hours ago
2
$begingroup$
Sorry, but this is off-topic here. This site is for working code only. The online judge seems to be the problem since the only difference isusing namespace std. Your best bet is to contact kattis. If you want this to be on-topic here, you can edit your question to ask how to improve either one of the two versions.
$endgroup$
– Null
4 hours ago
1
$begingroup$
The use of a non-standard include filebits/stdc++.his not good practice.
$endgroup$
– Edward
4 hours ago
$begingroup$
@Null it seems that you're saying there should be no difference -- which is exactly what I'm calling into question. If they are the same thing, why the side effects. and I will stop using bits, thanks. I wonder if that is causing some sort of clash.
$endgroup$
– user191196
4 hours ago
$begingroup$
Without the test cases we can't really say what the problem is. You could try to prefix all calls topow()andabs()withstd::as they are in the standard namespace, too.
$endgroup$
– Null
3 hours ago
$begingroup$
I don't have access to test cases from Kattis; however the best I can offer in terms of replication is to ask you to submit both versions at the Kattis link in the post; the "wrong" one fails test case 2
$endgroup$
– user191196
4 hours ago
$begingroup$
I don't have access to test cases from Kattis; however the best I can offer in terms of replication is to ask you to submit both versions at the Kattis link in the post; the "wrong" one fails test case 2
$endgroup$
– user191196
4 hours ago
2
2
$begingroup$
Sorry, but this is off-topic here. This site is for working code only. The online judge seems to be the problem since the only difference is
using namespace std. Your best bet is to contact kattis. If you want this to be on-topic here, you can edit your question to ask how to improve either one of the two versions.$endgroup$
– Null
4 hours ago
$begingroup$
Sorry, but this is off-topic here. This site is for working code only. The online judge seems to be the problem since the only difference is
using namespace std. Your best bet is to contact kattis. If you want this to be on-topic here, you can edit your question to ask how to improve either one of the two versions.$endgroup$
– Null
4 hours ago
1
1
$begingroup$
The use of a non-standard include file
bits/stdc++.h is not good practice.$endgroup$
– Edward
4 hours ago
$begingroup$
The use of a non-standard include file
bits/stdc++.h is not good practice.$endgroup$
– Edward
4 hours ago
$begingroup$
@Null it seems that you're saying there should be no difference -- which is exactly what I'm calling into question. If they are the same thing, why the side effects. and I will stop using bits, thanks. I wonder if that is causing some sort of clash.
$endgroup$
– user191196
4 hours ago
$begingroup$
@Null it seems that you're saying there should be no difference -- which is exactly what I'm calling into question. If they are the same thing, why the side effects. and I will stop using bits, thanks. I wonder if that is causing some sort of clash.
$endgroup$
– user191196
4 hours ago
$begingroup$
Without the test cases we can't really say what the problem is. You could try to prefix all calls to
pow() and abs() with std:: as they are in the standard namespace, too.$endgroup$
– Null
3 hours ago
$begingroup$
Without the test cases we can't really say what the problem is. You could try to prefix all calls to
pow() and abs() with std:: as they are in the standard namespace, too.$endgroup$
– Null
3 hours ago
|
show 1 more comment
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$begingroup$
I don't have access to test cases from Kattis; however the best I can offer in terms of replication is to ask you to submit both versions at the Kattis link in the post; the "wrong" one fails test case 2
$endgroup$
– user191196
4 hours ago
2
$begingroup$
Sorry, but this is off-topic here. This site is for working code only. The online judge seems to be the problem since the only difference is
using namespace std. Your best bet is to contact kattis. If you want this to be on-topic here, you can edit your question to ask how to improve either one of the two versions.$endgroup$
– Null
4 hours ago
1
$begingroup$
The use of a non-standard include file
bits/stdc++.his not good practice.$endgroup$
– Edward
4 hours ago
$begingroup$
@Null it seems that you're saying there should be no difference -- which is exactly what I'm calling into question. If they are the same thing, why the side effects. and I will stop using bits, thanks. I wonder if that is causing some sort of clash.
$endgroup$
– user191196
4 hours ago
$begingroup$
Without the test cases we can't really say what the problem is. You could try to prefix all calls to
pow()andabs()withstd::as they are in the standard namespace, too.$endgroup$
– Null
3 hours ago