Fun C++ Problem

[RoboTact]

VC++6 compiler was a lot faster (to fail on wrong code) - but still took 30 minutes on 1GHz machine. Result is that there are indeed only 3 solutions.

- at 24:
int i, n = 20;
for (i=0;-i<n; i--)
{
cout << "x" << endl;
}


+ at 26:
int i, n = 20;
for (i=0; i+n; i--)
{
cout << "x" << endl;
}


n at 30:
int i, n = 20;
for (i=0; i<n; n--)
{
cout << "x" << endl;
}

[Andrea_Rossini]

Solution 4:

i=0;~i<n;i--

this doesn't work, in fact prints x 21 times due to differences between 1 and 2 's complement.

[sachin871]

Same Is the caser with me .....
Found these two first....

i=0;i<n;n--
i=0;-i<n;i--

Never thought of termination condition....

Gud one...
Guys post more puzzles of these kinds....

[AshokParikh]

Hi,

A nice one, it took me about 3 minutes to get first solution, then it was easy, I could get all the three in 5 mintes.

How is it going for others?

[JasonD]

I got all three of them in a few minutes, because I thought about the loop terminating with an answer that is not Boolean.

I really need to point out that such a puzzle is a bad interview question. Such puzzles are fun, but they are not a good indication of programming ability. More importantly, as Joel Spolsky says it, it doesn't show if the candidate is smart and gets things done. I highly recommend his article:

The Guerrilla Guide to Interviewing

Finally, avoid brain teaser questions like the one where you have to arrange 6 equal length matches to make exactly 4 identical perfect triangles. If it's an "aha!" question, you don't get any information about "smart/get things done" by figuring out if they happen to make the mental leap or not.

A great read. The puzzles are fun, no doubt. I love them. Just don't judge people based on how quickly they can solve it...

[sszd]

I really need to point out that such a puzzle is a bad interview question. Such puzzles are fun, but they are not a good indication of programming ability. More importantly, as Joel Spolsky says it, it doesn't show if the candidate is smart and gets things done.

The puzzles are fun, no doubt. I love them. Just don't judge people based on how quickly they can solve it...

Well put. I couldn't agree with you more.

[Zaccheus]

Yes, it's a strange interview question.

[JohnW@Wessex]

I found the first solution in the first minute, then I thought 'what a pointless exercise' and went off and did something more interesting instead.

[Matthew Doucette]

I finally got all three! I'll admit that it helped when the details of the problem were explained... as it hinted at where I should look for the third solution (which was -i<n for me).

[ZetaSolid]

Three, it is very tricky question

[pinchharmonic]

new here, found this fun problem through google.

i+n was definitely the hardest one! remembering that the loop condition is only false when negative helped =)

[Eri523]

i+n was definitely the hardest one! remembering that the loop condition is only false when negative helped =)

Congratulations that you found it (which I didn't ), but the loop condition is only false when zero!

Ah, and: Welcome to CG!

[whitevandal]

What about

int i, n =-20;

?

Took about 5 minutes. I never would have thought of n+1. More than 3 solutions, I guess. : )

[Alterah]

Got all three. Surprisingly I don't think the third solution took me as long as the second solution.

[VladimirF]

What about

int i, n =-20;

?

Took about 5 minutes. I never would have thought of n+1. More than 3 solutions, I guess. : )

If n is -20, i=0 will never be less than n.
Interestingly, since I didn’t want to read past the first few posts, I did not realize that I played this game five years ago, and accidentally found (again) all three solutions. Again without timing; about 10 minutes, I guess.
Do I get a double bonus?