Why does this problem print 2?

Question

int[] a = {100,89,6,3};
for(int i=1;i<a.length;i++)
a[i] = a[i-1] % a[i];

System.out.pritnln(a[3]);

Answer 1

you need previous value of a[3] & value of a[2] at that time, to calculate modified value of a[3]

a[1]=a[0]%a[1]; //a[1]=100%89=11
a[2]=a[1]%a[2]; //a[2]=11%6=5
a[3]=a[2]%a[3]; //a[3]=5%3=2

Answer 2

Let's look at it in details so that you understand it.
Here's the original array: int[] a = {100,89,6,3};

first iteration i = 1
a[1] = a[1 - 1] = 100 % a[1] = 89
a[1] = 100 % 89 = result 100/89 = 1, remainder 11
new int array int[] a = {100,11,6,3};

Second iteration i = 2
a[2] = a[2 - 1] = 11 % a[2] = 6
a[2] = 11 % 6 = result 11/6 = 1, remainder 5
int[] a = {100,11,5,3};

Third iteration i = 3
a[3] = a[3 - 2] = 5 % a[3] = 3
a[3] = 5 % 3 = result 5/3 = 1, remainder 2
int[] a = {100,11,5,2};

int[] a = {100,11,5,2};
a[3] is 2

I recommend you run the code with some prints to help you understand it:

for(int i = 1; i < a.Length; i++)
{
a[i] = a[i - 1] % a[i];
Console.WriteLine("Elements of a: {0}, {1}, {2}, {3}", a[0], a[1], a[2], a[3] );
Console.WriteLine(a[i]);
}

Answer 3

5 % 3 = 2

Answer 4

@tobias
5?