The first conditional sentence inside the chooseOperation method didn't allow to the calculator to introduce negative numbers as a first input given that everytime the '-' button was pressed it checked for the string and being the string empty it returned nothing, with the new if statement now it can recive negative numbers as input.
The first conditional sentence inside the chooseOperation method didn't allow to the calculator to introduce negative numbers as a first input given that everytime the '-' button was pressed it checked for the string and being the string empty it returned nothing, with the new if statement now it can recive negative numbers as input.