Day of Year Program help!

[fbhkhan]

Modify the DayOfYear class, written in the earlier program, to add a constructor
that takes two parameters: a string representing a
month and an integer in the range 0
through 31 representing the day of the month. The constructor should then initialize the integer member of the class to represent the day spcified by the month and day of month parameters. The constructor should terminate the program with an appropriate error message if the number entered for a day is outside the range of days for the month given.

Add the following overloaded operators:

++ prefix and postfix increment operators. These op
erators should modify the
DayOfYear object so that it represents the next day
. If the day is already the end of the
year, the new value of the object will represent th
e first day of the year.
-- prefix and postfix decrement operators. These op
erators should modify the DayOfYear
object so that it represents the previous day. If t
he day is already the first day of the year,
the new value of the object will represent the last
day of the year

Situation:
I have done the previous program which takes a number of the day of a year and returns a month and day but i dont understand this part! Dont know where to put the prefix, postfix and overloaded operator. Im kinda lost please help!

#include <iostream>
#include <string>
#include<cstdlib>

using namespace std;

class dayOfYear {

private:
    int userDay;    // private class member to hold user input
    string month;
public:
    dayOfYear();    //Constructor
    void setMonth(string);  //set the month
    string setUserMonth();  // set user month
    void setDay(int);   // Function to set day
    int getDay()const;  // Function to recieve day for later functions
    void print() const; // Print() function

    dayOfYear(string, int);    //Constructor thats takes in 2 parameter...
};

dayOfYear::dayOfYear() : userDay(0) { }     //Constructor initializing userDay to 0, no other initializations.

void dayOfYear::setMonth(string month) { this -> month = month; }
void dayOfYear::setDay(int userDay) { this -> userDay = userDay; }       // Setting user input to userDay
int dayOfYear::getDay() const { return this -> userDay; }        // Return this->userDay to calling function

dayOfYear::dayOfYear(string m_name, int m_day)
{
    if (m_day > 0 && m_day < 31)
        userDay = m_day;
    month = m_name;
}

void dayOfYear::print() const {         // Print out all relevant information
    string months[] = {"", "January", "February", "March", "April",  "May",  "June", "July", "August", "September", "October", "November", "December"};
    int days_in_month[] = {0, 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31};

    for (int i=1; i<= 12; i++)
    {
        if((month.compare(months[i]) == 0) && userDay <= days_in_month[i] && userDay > 0)
        {//January
            cout << month << "  " << userDay << ": " << endl;// Print it out =)
            return;
        }
    }
    cout << "Invalid month or days in month.";
}

//Exactly as it sounds, get the user input of the day
int getUserDay() {
    int number;
    while(true) {
        cout << "Please enter the day of the month: ";
        cin >> number;
        cin.ignore();
        if(number > 0 && number < 366) {break; }
        cout << "You entered an invalid number!!\n\n" << endl;
    }
    return number;
}

string getUserMonth() {
    string month;
        cout << "Please enter the month: ";
        cin >> month;
        while(true) {
            if(month.compare("january") == 0 || month.compare("January") == 0) {
                month = "January" ;
                 break;
            }
            if(month.compare("february") == 0 || month.compare("February") == 0)  {
                month = "February" ;
                break;
            }
            if(month.compare("march") == 0 || month.compare("March") == 0)  {
                month = "March";
                break;
            }
            if(month.compare("april") == 0 || month.compare("April") == 0)  {
                month = "April";
                break;
            }
            if(month.compare("may") == 0 || month.compare("May") == 0)  {
                month = "May";
                break;
            }
            if(month.compare("june") == 0 || month.compare("June") == 0)  {
                month = "June";
                break;
            }
            if(month.compare("july") == 0 || month.compare("July") == 0)  {
                month = "July";
                break;
            }
            if(month.compare("august") == 0 || month.compare("August") == 0)  {
                month = "August";
                break;
            }
            if(month.compare("september") == 0 || month.compare("September") == 0)  {
                month = "September";
                break;
            }
            if(month.compare("october") == 0 || month.compare("October") == 0)  {
                month = "October";
                break;
            }
            if(month.compare("november") == 0 || month.compare("November") == 0) {
                month = "November";
                break;
            }
            if(month.compare("december") == 0 || month.compare("December") == 0) {
                month = "December";
                break;
            }
        cout << "You have misspelled the month " << month << " please re-enter! ";
        cin >> month;
        }
       return month;
}

	// Pass the class dayOfYear as printC() argument so it can access the members
void printC(dayOfYear &D) {
    cout << endl;
//  cout << D.getDay() << ": " ;    // Get the day the user defined in the beginning
    D.print();      // Print all the lovely information for the user =)
    cout << "\n\n\n\n";
}

int main() {
    dayOfYear D;        // D represents dayOfYear class
    D.setMonth(getUserMonth()); // Set the month by calling getUserMonth, than transferring info to setMonth
    D.setDay(getUserDay()); // Set the day by calling getUserDay, than transferring to setDay to do so.

    printC(D);  // printC is passing the class dayOfYear which is D as it's argument so it can access the elements in the class

    return 0;
}