In C++

USE main.cpp, calculator.cpp and calculator.h

Problem 2 In this problem, you will implement undo and redo functionality for a calculator that performs only add or subtract operations. A user's actions may perform add or subtract operation on the last output of the calculator. After each action, the user may perform an undo or redo operation until such an operation is possible. Undo operation invalidates the last operation performed, and redo performs the last undone operation. E.g., the user has already performed the actions as follows (calculator starts with a value 0) i. Add 1 ii. Add 14 ii. Subtract 6 v Add 4 At this point, the result of the calculation is 13. Now, an undo operation undoes the most recent operation, i.e., "Add 4" is undone, and the calculator output becomes 9. Another undo operation undoes the operation before it, and the calculator output becomes 15. A redo operation redoes the last operation that was undone, i.e., calculator output becomes 9. Another redo operation makes the output go back to 13. At this point no more undo operations are possible