Initial task from: Microsoft and extra challanges added from: The C# School
My improvements:
- Changed that menu is at the begining of the program and only then numbers are asked for.
- Seperated code for where 1 and whre 2numbers needed for operation.
- Handled big/small letters for input, updated Regex
- Added quit option
- Changed Json structure how it is written and read.
- Handled better getting previous results
- Handled possible null reference exceptions
- ...extra coments for more difficult parts for the future for myself :)