Difference between 'for index' and traditional 'for loop' - swift

Question

I'm new to Swift and pretty new to programming. I'm not sure if it's because it's 2:34 am but can somebody help me identify the difference between these two loops?
The first one is resulting in the values I want yet uses (as the Swift documentation explains) a 'traditional C loop' where the one after is using what seems like a Swift preferred 'for index' loop (which I personally like as it is clearer to me), the problem is that this loop returns every number rather than meeting the conditional.
func findLargestPrimeFactor(number: Int) {
for var i = 2; i < number; i += i {
if number/i % 1 > 0 {
} else {
print(i);
}
}
}
findLargestPrimeFactor(13195);
Below is returning every number to 13195
func findLargestPrimeFactor(number: Int) {
for i in 2...number {
if number/i % 1 > 0 {
} else {
print(i);
}
}
}
findLargestPrimeFactor(13195);

Answer 1

I've realised how stupid my mistakes were, first of all I have no idea why I was doing i += i, that just didn't make sense at all.
Also, my conditional was never being met because I declared it as an Int when really I needed a Float because I care about remainders!
Edit: I've updated my code yet again (taken everyones feedback into consideration), I feel a bit better with this and will continue working on the solution.
Thanks to everyone for your help!
Updated code
func findLargestPrimeFactor(number: Int) {
for i in 2...number {
var n = Float(number)
var count = Float(i)
if n/count % 1 > 0 {
print("not divisible")
} else {
print(i)
}
}
}
findLargestPrimeFactor(13195);