In progress Calculator with GUI

just a little thingy to stay occupied during semester holidays
its very much work in progress :D

current TODO:

- add saving functions
- add functionality for negative numbers

completed tasks:

- make calc able to calculate with more than 2 numbers and make it respect math rules ("*" and "/" first)
- GUI looks presentable
- "(" and ")" with functionality
- error handling (division with 0)
- user input via keyboard (just the displayLabel a textfield)
- basic tracking and saving within one session