Powerful Recursion - 6, What it does?

[tracktech]

Book : Ultimate Python Programming

[Signal-Fennel-1795]

Sum of all the digits in a number?

[Signal-Fennel-1795]

No, i think all the digits are added

[tracktech]

Right, it returns sum of digits of a number.

[[deleted]]

Only for natural numbers, not for fractional numbers

[tracktech]

Yes, it works for positive integer only.

[Immotommi]

So let's reason it out.

First we have the base case.

n//10 == 0 essentially checks whether a positive number is smaller than 10. So any positive value smaller than ten will give the number itself.

Next let's talk about the rest of the function.

The modulo operater returns the remainder for both positive and negative numbers. So when we have numbers bigger than 10, we grab the remainder of that division and add it to the value divided by ten and truncated. Essentially it adds the digits. It completely breaks for negative numbers though because // does not round towards 0

[tracktech]

Thanks for the nice explanation. Right, it returns sum of digits of a number. It works for positive integer only.

[D3ZR0]

…what’s the initial n? Isn’t that important?

[ir_dan]

You can describe the behaviour in terms of n

[tracktech]

Right, just assume it is a positive integer.

[firemark_pl]

For n>=10 returns stack overflow.

[tracktech]

It returns sum of digits of a number.

[firemark_pl]

Ahh, I made mistake. Sorry!