Printing a value changes the output of the code - c++

Question

Few hours ago, a competition was held on CodeForces , this was one the questions of the competition -
Problem C (You dont have to read/solve it to answer the question)
EDIT : Adding the question here as requested, again, one does not necessarily have to read it.
Slastyona and her loyal dog Pushok are playing a meaningless game that
is indeed very interesting.
The game consists of multiple rounds. Its rules are very simple: in
each round, a natural number k is chosen. Then, the one who says (or
barks) it faster than the other wins the round. After that, the
winner's score is multiplied by k2, and the loser's score is
multiplied by k. In the beginning of the game, both Slastyona and
Pushok have scores equal to one.
Unfortunately, Slastyona had lost her notepad where the history of all
n games was recorded. She managed to recall the final results for each
games, though, but all of her memories of them are vague. Help
Slastyona verify their correctness, or, to put it another way, for
each given pair of scores determine whether it was possible for a game
to finish with such result or not.
Input In the first string, the number of games n (1 ≤ n ≤ 350000) is
given.
Each game is represented by a pair of scores a, b (1 ≤ a, b ≤ 10^9) –
the results of Slastyona and Pushok, correspondingly.
Output For each pair of scores, answer "Yes" if it's possible for a
game to finish with given score, and "No" otherwise.
You can output each letter in arbitrary case (upper or lower).
So I solved it, and after the competition was over, me and my friends were discussing the problems when they asked me what was my answer coming for the following test case -
1
1 1
I said it was "Yes" on my IDE (Dev-C++ 5.11), (as it was supposed to be)
But when we ran it on ideone, it came out to be "No" !!
I thought there must be a problem with my code only, so i tried debugging it when i came across this problem,
My Code -
#include<stdio.h>
using namespace std;
long long int iscube(long long int n)
{
long long int lo = 0;
long long int hi = 1000000;
while(lo < hi)
{
long long int mid = (lo+hi)/2;
if(mid*mid*mid < n)
lo = mid+1;
else
hi = mid;
}
return lo;
}
int main()
{
long long int a,b;
int n;
scanf("%d",&n);
while(n--)
{
scanf("%I64d %I64d",&a,&b);
long long int c = a*b;
long long int cb = iscube(c);
//printf("%lld",cb)
if(cb*cb*cb == c)
{
if(a%cb == 0 && b%cb == 0)
printf("Yes\n");
else
printf("No\n");
continue;
}
printf("No\n");
}
}
When i give the input as
1
1 1
in the above code, the answer comes out to be "No"
BUT if I ONLY uncomment the line above the if statement in the while loop in the main() function,
the answer would be "1 Yes"
(these outputs are the outputs i got when i ran the code on ideone, when running on Dev-C++ 5.11 , i got "Yes" and "1 Yes" as expected)
Now while i was thinking that my my answer of codeforces would be evaluated as WA, After the system test, it came out to be Accepted!
Does anyone have any idea on why this issue is arising?
(Also, could someone add the appropriate tags, if any)

Answer 1

Turn up your warnings, you have undefined behavior in your scanf:
warning: length modifier 'I64' results in undefined behavior or no effect with 'd' conversion specifier [-Wformat]
scanf("%I64d %I64d",&a,&b);
If you change it to scanf("%lld %lld",&a,&b); (C++11), then you'll have defined behavior, however since you're using C++, just use a stream instead:
std::cin >> a >> b;
Demo