Making a calendar

[An Integer]

I am making a calendar that should just have some basic features. Like setting dates and checking spesific dates. I've made a class for setting dates, which also checks if it's a valid date. For example, a month can't exceed 12, and a day can't exceed 7. Here's the code for that:

class Calendar {
public:
	void setDate(int d, int m, int y) {

		bool day_check = false; bool month_check = false;

		if (m < Month::January || m > Month::December) {
			cerr << "Month does not exist." << endl;
		}
		else {
			month_check = true;
		}

		if (d < Day::Monday || d > Day::Sunday) {
			cerr << "Day does not exist." << endl;
		}
		else {
			day_check = true;
		}

		if (month_check == true && day_check == true) {
			year = y;
			month = m;
			day = d;
		}
		else {
			cerr << "Error with checking dates!" << endl;
		}
	}

	enum Month {
		January = 1,
		February,
		March,
		May,
		June,
		July,
		August,
		September,
		October,
		November,
		December
	};

	enum Day {
		Monday = 1,
		Tuesday,
		Wednesday,
		Thursday,
		Friday,
		Saturday,
		Sunday
	};

	friend ostream& operator <<(ostream& os, Month m) {
		return os << month_table[m]; // Checking a vector with strings Jan - Dec.
	}
	friend ostream& operator <<(ostream& os, Day d) {
		return os << day_table[d]; // Checking a vector with strings Mon - Sun.
	}

	int getYear() { return year; }
	Month getMonth() { return Month(month); }
	Day getDay() { return Day(day); }

private:
	int year;
	int month;
	int day;
};

But now I'm kinda unsure of how to take it even further. How could I extend my project to make it more like a full program rather than a thing that does one job?

The code works as it is right here. But it's kinda boring just using:

Calendar cal;

cal.setDate(1,2,2017);

Any good ideas on how I can ask the user (of the program) for inputs on dates that should be stored, or maybe another class for "booking" of dates?