[rightbyte]

If you when calculating an average actually reach overflow in a double without messing up the precision first and making the calculation worthless in the first place, some numbers in the list of numbers is bogusly big anyway.

[Ragib_Zaman]

Or the list is just very long.

[gubbrora]

Not really. The time required to overflow that way is unrealistic. Also I think you'll run into S + x = S. at that point your sum will stop climbing towards overflow.