steps are printed out without counter
[Feature] add a New Operator Feature
[Add] Apply OCP in Operator Class (Addition, Subtraction, Multiplication, Division)
[Modify] modify existing code calling Operators
Merge commit '5c2261ff6d11fcad3509bf3c821209bc7101dc06' into feature/New-Operator
Merge remote-tracking branch 'origin/feature/New-Operator' into feature/Refactoring
Warning!!! This code does not finish.
Able to run, but still have bug in creating a Expression Tree
solve some building tree bug, more test case pass
Merge commit '39c2688a9fcd8669d562c93b8ae2812c2b2abd36' into feature/Refactoring
fix some error after merge