Good job. You might want to add some more functions though. For example, the builtin sqrt(); function should be easy to implement. You could even check out greatest common factor by one of our fellow monks. With all that, you could carry this program on to be better than what it already is.Some other easy ideas would be to use powers (1 ** 2 1 to the second power) and simple modulus (4 %  3).

Future: Use these math functions: tan, sin, cos, Lowest terms (for fractions), area, perimeter, and so on...

Almost a Perl hacker.
Dave AKA damian
I encourage you to email me