Like was mentioned, the simplest behavior is treat this as an error case. Other possibilities include: (*) extending the length of the short array to match th

Like was mentioned, the simplest behavior is treat this as an error case. Other possibilities include: (*) extending the length of the short array to match the length of the long array -- padding with zeros on the right -- before adding. (*) finding all possible sums between pairs with one number from one array and the other number from the other array. (*) cyclically extending the shorter array (probably not useful in this example, but since the example didn't come with a use case that's difficult to know for sure). (*) Treating each array as a decimal number (or a number in some other base) (*) combining the two array as a single list of numbers and summing everything to a single value and... so on... One point being that programming languages support arbitrarily complex operations. Another point being that "sum" in this context carries some understandable ambiguity -- the sort of thing which we usually try to constrain with use cases or examples or similar elaboration.