Write a pure virtual function occurs$\_$on$($int year, int month, int day$)$ that checks whether the appointment occurs on that date.$$ For a monthly appointment, only the day and year must match; for a day appointment, all three fields must match.

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Fill in a vector of Appointment pointers with a mixture of appointments. $$Have the user enter a date and print out all appointments that happen on that date.

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Write a program that tests each function and displays the results of their use.