You don't need parentheses, it will multiply first and then subtract, even if you put a minus sign before the multiplication.

I didn't know that cause that's not what you said in your comment. That's still slower for large number sizes, e.g 32 bit integers (the most common size for an integer in cpp), although if we're being specific since we're dealing with signed integers here, so the max would be like 2^31 - 1. I agree that for small numbers, the iterative method is faster, but not by much as both methods are practically instant when dealing with small numbers. It's better to make the function scalable to larger numbers by using this method.

It's funny because this was actually pretty much my original answer, except that I didn't account for numbers less than zero.
The error message wasn't very helpful, so I found myself jumping through hoops trying to figure out how to handle floating point inaccuracies.

Seemed like a simple task, but I broke my head solving it, 2 out of 3 conditions in the task were met and the last one was not accepted by me. Of course, I had to resort to help....... It turned out to be the same thing I wrote, just with some minor changes, which also turned out to be tricky, but now I see that it's even easier. I'm going to be a wreck today, work in 4 hours and I haven't slept.....

agree.