You work for the Foobar Company, and you are assigned the project Calculator. It is a very old, unmaintained project, which has got some quality issues.
At the moment, the Calculator only supports sums; the Customer required a new functionality: the possibility to specify additional operations (substract, multiply and divide) to be performed on the two provided arguments. You should implement the required functionality and improve the code quality.
You are kindly asked to provide your result as an independent GitHub repository (not a fork), or as a zip file.