Simple Swift Fibonacci program crashing (Project Euler 2)

Question

I am trying to solve the second problem on Project Euler. The problem is as follows:

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Each new term in the Fibonacci sequence is generated by adding the pre

Answer 1

There is nothing weird about this at all. Do you know how large the 400 fibonacci number is?

176023680645013966468226945392411250770384383304492191886725992896575345044216019675

Swift Int64 or UInt64 simply cannot handle that large of a number. The later can go up to 18446744073709551615 at max - not even close.

If you change your variables to be doubles it works but will be inaccurate:

var prev : Double = 0
var next : Double = 1
var num : Double = 0
var sum : Double = 0

will yield

2.84812298108489e+83

which is kind of close to the actual value of

1.76e+83

Luckily you do not need to get values that big. I would recommend not writing a for loop but a while loop that calculates the next fibonacci number until the break condition is met whose values do not exceed four million.