Sum error in an array iteration

Question

I started at Ruby the other day and I have a question. I was doing the Hackerrank exercises and in a certain exercise it was necessary to do the sum of the array elements, not simple? Yes. But my ruby code had an error message:

def sum(n, arr)
    sum = 0
    for i in (0..n) do
        sum += arr[i]
    end
    return sum
end

Error:

Solution.Rb:6:in +': nil can't be coerced into Integer (TypeError) from solution.rb:6:inblock in simpleArraySum' from Solution.Rb:5:in each' from solution.rb:5:insimpleArraySum' from Solution.Rb:15:in `'

Javascript equivalent code:

const sum = function (n, arr) {
    let sum = 0;
    for (let i = 0; i < n; i++) {
        sum += arr[i];
    }
    return sum;
};

Answer 1

After searching a little about it I saw that I was changing the syntax, when used (0..n) with two points means that the n is included in the iteration.

In this case you should have used (0...n) not to include it.