Ruby, returning the nth triangular number and returning 0 for out of range values

Question

I'm currently doing some Code Wars training and am having trouble with the nth triangular test.

Here is the question:

You need to return the nth triangular number. You should return 0 for out of range values, but you will always be passed a number.

Here is my current code when n is being passed with only the values of 1, 2, and 3 (which is all that is needed to pass the test).

# Return the nth triangular number
def triangular( n )
 n * (n + 1) / 2
end

I continue to get a most of the tests passed, except I get an error:

Expected: 0; instead got: 10

If someone could kindly explain what this is even asking that would be great, can't seem to find any material online that explains this problem.

Answer 1

Your formula seems valid, so that must be related to the out-of-range numbers. If you got "10 instead of 0", then maybe the input data has a case of "-5" which would result in -5 * -4 / 2 = 10, but of course there should be no answer for "-5" hence expected is zero.