I have to do the Exact same assignment for one of my classes. I'm not sure if you know this or not, just trying to be helpful, but it is possible to only need one function for adding and subtracting, such that a-b = a+-b. All you have to do is pass the "b" as a negative number. Same for multiplying and dividing, a/b / c/d = a\b * d/c.
You probably already know this, but just trying to put in some feedback. Everyone else's comments have helped me also. Thanks