in math, if you have a real and you round it, it's always a real not an integer.

No, that's made up. Outside of very specific niche contexts the concept of a number having a single well-defined type isn't relevant in math like it is in programming. The number 1 is almost always considered both an integer and a real number.

If we follow your mind with abs(-1) of an integer it should return a unsigned and that makes no sense.

How does that not make sense? abs is always a nonnegative integer value, why couldn't it be an unsigned int?