How can I use function that return object data type in constructor?

class DayOfYear
{
	private:
		int day;
		string month;
	public:				
		DayOfYear(){}
		DayOfYear(int d){
			day = d;
			month = "";   // here, what I ve to put to get string i e 
 "January" or "Feb" from convert() function?
		}
	
		DayOfYear convert()           
		{
			if(day<=31 && day >=1)
				month = "January";
					
			else if(day<=59){
				day = day-31;
				month = "February";
			}
            else{
                 "Invalid Input";
            }
           return 0;
         }
};