DBAtrix is certainly correct. The question is what you expect the result to be when a value is divided by 0. There are mathematical arguments for both infinity and undefined. We have no way to represent infinity, but we do have NULLs to represent undefined. Therefore, the standard way this is handled is:

SELECT
---:Numerator / DECODE ( :Denominator, 0, NULL, :Denominator)
FROM
---DUAL

Hope this helps,

- Chris