Just functions that manipulate them... I was making a program that finds odds/evens... and orders them big to small based on that criteria.
I was simply looking for tools that manipulate them to see if any would be of any use... and to know them for the future for more complex programs etc.
You want to get the number of digits in a number? You could convert it to a string and then get the length. Though there are faster ways to do that (at least for integers. with doubles it's a bit more complicated..)