Understanding Private and Public Members in C++ Classes: A Practical Example

a) If we remove the // from the line '// m = today.month;', the line becomes part of the program again. Building the program will then result in an error because the line tries to access the private member variable 'month' of the class 'Date'.

b) To fix the error, we can change the line 'private:' to 'public:' in the class definition. This change will make the member variable 'month' accessible from outside the class, and building the program should no longer result in an error. Changing the access specifier from 'private' to 'public' allows external code to access and modify the member variable 'month'.