Why do we need Functions?

[bartok]

SUB Arrotonda! (num!)
    Arrotonda! = _ROUND(num! * 100) / 100
END SUB

because the "!" is not admited and, without the "!", we will have:

SUB Arrotonda (num!)
    Arrotonda = _ROUND(num! * 100) / 100
END SUB

This is incorrect syntax either way because the name of the "SUB" cannot be used in assignment. Must be a "FUNCTION" instead.

For the first, it was just a demostration about that fact that it didn't work.
For the second, do you like better like this:

SUB Arrotonda (num!)
    num! = _ROUND(num! * 100) / 100
END SUB

I don't have changed "Arrotonda" with "num!"
This doesn't change nothing about what I said. I know that it must be a FUNCTION. In fact I use a FUNCTION and this is the reason why when I made the example as a SUB I forgot the changing. But all the reasoning made, was just to explain in what cases it is better a FUNCTION then a SUB and how avoiding FUNCTIONs in favor of SUBs leads, in these cases, to do things that can be made in a simple way, in a very complicated one. But thank's you for the correction.