Some quirks of my design. There is no unary negative operator. Instead, the minus button acts as both depending on if the follows another operator or not. Also if you try to input two operators excluding the unary one it will replace the previous one with the newest one stopping you from say adding multiply 3.
Here is a link for those that just want a quick look.
For those interested in how it works, allow me:
Under the hood every key press you make is tested to see if it is valid then put on a stack and the display is updated. When you hit equals the stack is sorted so all the individual digits are combined into full numbers. Then the maths is handled, with order of operations dealt with through a recursive method of breaking down the sum. Then the total is spit back out.
Here and here you can see partially complete versions which show my approach of getting the thing to work first!
Anyways please fell free to break it or give any feedback