Fibonacci sequence problem

[chrisname]

Not sure what to put in the title...

Quite recently I took to trying to solve problems on "ProjectEuler.net". It's a website with loads of maths problems to solve... I ran out of ideas for things to do a while ago and someone told me about the website. So I've been doing the problems on there.

I've written this code and it outputs the answer 627587869, which I am sure is wrong. I have no idea what is wrong with the code though (it is me, not the compiler, I am sure. I am using Dev-C++ so I know it isn't the compiler's problem).

If you're wondering why I am using long, it is because it was outputting things like -138348534578304897580346873469073086 (intense exaggeration) and I thought it might be because the number is too big for an integer, and didn't change it back.

The answer is apparantly 4613732, and I have no idea how to reach it.

Please don't write the program for me, just some tips would be good.

#include <iostream>

long Fib() {

long fib1=0, fib2=1, fibr, n=4000000;

for (int i=n; i>0; i--) {
    fibr=fib1+fib2;
    fib1=fib2;
    fib2=fibr;
}
return fibr;
}

using namespace std;

int main() {
cout << "The sum of all even numbers in the Fibonacci sequence which are lower than four million is: " << Fib() << endl;
cin.get();
return 0;
}

[Duthomhas]

It is because a long doesn't have enough bits to store fib(4000000). [I don't think the computer as a whole has enough bits.]

As a hint:

fib( 33 ) --> 3,524,578
fib( 34 ) --> 5,702,887


Hope this helps.

[chrisname]

I'm not sure I understand your hint.

Thanks for helping though.

[Duthomhas]

You want the sum of even fibonacci numbers less than 4,000,000, right?

So that's the sum of all the even numbers for n in [0,33].

Hope this helps.

[chrisname]

Ohh! Thanks! Can't compile right now as I'm at school (it's 8:15AM in the UK), so I'll try that when I get home.