How to make user input calculations?
 

I want to make a calculator for Alice. So if the user puts in 4*5 it comes out with 20 etc. I also need it to pick out the largest to smallest number, for example, I put in 1,2,3,4,5 the calculator gives me 5,4,3,2,1. Then I want it to add, so 4+5+5+5=19.

I need to be able to do this with arrays I think, but I'm not sure how to do this at all and I would love some help thank you!