You will need to (1) Create an interface to create your calculator, and (2) implement the calculator code.
I want you to use a standard linked list (not array) to do this assignment - and put in checking for correct entry of numbers and operators. You can use code you already have. All code you write can be completely independent of my code if you write it correctly. My stack would simply be an object you can use. Also in case you had not noticed.