Class Increment and Decrement operators not working?

[Toasthat]

First let me start by saying that my code was too long for this post so down inbetween where it says >>START and <<END is where I put my increment and decrement operator functions. I will post them in the first comment. They were VERY long. My problem is that the increment and decrement post and prefix operators seem to not be working correctly. The increment will increase the day by 1 but not cycle to the next month if the day goes out of bounds and the decrement seems to do nothing. Maybe plug em in and see what you get so you understand what I'm saying?

#include <string>
#include <iostream>

using namespace std;

class DayOfYear
{
   private:
      
      static int day;//stores the integer input by user into class
      static string month;//stores the message for date output
      
   public:

      DayOfYear& operator++();//increment operator prefix
      DayOfYear& operator--();//decrement operator prefix      
      
      DayOfYear operator++(int);//increment operator postfix
      DayOfYear operator--(int);//decrement operator postfix
      
    
            
      DayOfYear(string classMonth, int classDay)//constructor
      {
         day = classDay;
         month = classMonth;
         
         if(day >= 1 && day <= 31)
         {
            if(day > 28)
            {
               if(month == "FEBRUARY")
               //won't allow february to have a 29th,30th, or 31st
               {
                 month = "NOTHIN";
               }
               else if(day > 30)
               {
                  if(month == "APRIL")
                  {
                     month = "NOTHIN";
                  }
                  else if(month == "JUNE")
                  {
                     month = "NOTHIN";
                  }
                  else if(month == "SEPTEMBER")
                  {
                     month = "NOTHIN";
                  }
                  else if(month == "NOVEMBER")
                  {
                     month = "NOTHIN";
                  }
               }
                  
              }

           }
           else
           {
            month = "NOTHIN";
           }
      }
  
  void print()//function that outputs the string in month-day format
  {
               
     if(month == "NOTHIN")//checks to see if the constructor received bad input
     {
      cout << "INCORRECT INPUT";
     }
     if(month == "JANUARY")//checks to see if day is within january
     {
        cout << month << " " << day << "\n";
     }
     else if(month == "FEBRUARY")
     {
        cout << month << " " << day << "\n";
     }
     else if(month == "MARCH")
     {
        cout << month << " " << day << "\n";
     }
     else if(month == "APRIL")
     {
        cout << month << " " << day << "\n";
     }
     else if(month == "MAY")
     {
        cout << month << " " << day << "\n";
     }
     else if(month == "JUNE")
     {
        cout << month << " " << day << "\n";
     }
     else if(month == "JULY")
     {
        cout << month << " " << day << "\n";
     }
     else if(month == "AUGUST")
     {
        cout << month << " " << day << "\n";

     }
     else if(month == "SEPTEMBER")
     {
        cout << month << " " << day << "\n";
     }
     else if(month == "OCTOBER")
     {
        cout << month << " " << day << "\n";

     }
     else if(month == "NOVEMBER")
     {
        cout << month << " " << day << "\n";
     }
     else if(month == "DECEMBER")
     {
        cout << month << " " << day << "\n";
     }
  }
     

};

>>START

<<END
   
   
string DayOfYear::month = "";//declares the static string
int DayOfYear::day = 0;//declares the static int    


int main()
{
   string monthInput;//used to pass the month to the class
   int dayInput;//used to pass day to the class
   cout << "Enter an integer from 1 to 31 for the month: ";
   cin >> dayInput;
   cout << "Enter a string for a month all uppercase: ";
   cin >> monthInput;
   DayOfYear doy(monthInput, dayInput);//creates a DayOfYear object in int main
   doy.print();//outputs the month and day format
   cout << "\nHere is the post incremented date: ";
   (doy++).print();
   cout << "\n";
   cout << "Here is the post decremented date: ";
   (doy--).print();
   cout << "\n";
   cout << "Here is the pre incremented date: ";
   (++doy).print();
   cout << "\n";
   cout << "Here is the pre decremented date: ";
   (--doy).print();
   cout << "\n";
   return 0;
}

[Toasthat]

Here are the increment and decrement operators that go between >>START and <<END

DayOfYear& DayOfYear::operator++()
  {
    ++day;
    if(day > 29)
    {
       if(month == "FEBRUARY")
       {
          day = 1;
          month = "MARCH";
       }
       else if (day > 30)
       {
          if(month == "APRIL")
          {
             day = 1;
             month = "MAY";
          }
          else if(month == "JUNE")
          {
             day = 1;
             month = "JULY";
          }
          else if(month == "SEPTEMBER")
          {
             day = 1;
             month = "OCTOBER";
          }
          else if(month == "NOVEMBER")
          {
             day = 1;
             month = "DECEMBER";
          }
       }
       else if(day == 31)
       {
          if(month == "JANUARY")
          {
             day = 1;
             month = "FEBRUARY";
          }
          else if(month == "MARCH")
          {
             day = 1;
             month = "APRIL";
          }
          else if(month == "MAY")
          {
             day = 1;
             month = "JUNE";
          }
             else if(month == "JULY")
          {
             day = 1;
             month = "AUGUST";
          }
          else if(month == "AUGUST")
          {
             day = 1;
             month = "SEPTEMBER";
          }
          else if(month == "OCTOBER")
          {
             day = 1;
             month = "NOVEMBER";
          }
          else if(month == "DECEMBER")
          {
             day = 1;
             month = "JANUARY";
          }
        }
     }
}  
   
DayOfYear DayOfYear::operator++(int)
{
    int temp = day;
    temp++;
    if(temp > 29)
    {
       if(month == "FEBRUARY")
       {
          temp = 1;
          month = "MARCH";
       }
       else if (temp > 30)
       {
          if(month == "APRIL")
          {
             temp = 1;
             month = "MAY";
          }
          else if(month == "JUNE")
          {
             temp = 1;
             month = "JULY";
          }
          else if(month == "SEPTEMBER")
          {
             temp = 1;
             month = "OCTOBER";
          }
          else if(month == "NOVEMBER")
          {
             temp = 1;
             month = "DECEMBER";
          }
       }
       else if(temp == 31)
       {
          if(month == "JANUARY")
          {
             temp = 1;
             month = "FEBRUARY";
          }
          else if(month == "MARCH")
          {
             temp = 1;
             month = "APRIL";
          }
          else if(month == "MAY")
          {
             temp = 1;
             month = "JUNE";
          }
          else if(month == "JULY")
          {
             temp = 1;
             month = "AUGUST";
          }
          else if(month == "AUGUST")
          {
             temp = 1;
             month = "SEPTEMBER";
          }
          else if(month == "OCTOBER")
          {
             temp = 1;
             month = "NOVEMBER";
          }
          else if(month == "DECEMBER")
          {
             temp = 1;
             month = "JANUARY";
          }
        }
     }
}  
   
DayOfYear& DayOfYear::operator--()
{
    --day;
    if(day == 0)
    {
       if(month == "JANUARY")
       {
          day = 31;
          month = "DECEMBER";
       }
       else if(month == "FEBRUARY")
       {
          day = 31;
          month = "JANUARY";
       }
       else if(month == "MARCH")
       {
          day = 29;
          month = "FEBRUARY";
       }
       else if(month == "APRIL")
       {
          day = 31;
          month = "MARCH";
       }
       else if(month == "MAY")
       {
          day = 30;
          month = "APRIL";
       }
       else if(month == "JUNE")
       {
          day = 31;
          month = "MAY";
       }
       else if(month == "JULY")
       {
          day = 30;
          month = "JUNE";
       }
       else if(month == "AUGUST")
       {
          day = 31;
          month = "JULY";
       }
       else if(month == "SEPTEMBER")
       {
          day = 31;
          month = "JULY";
       }
       else if(month == "OCTOBER")
       {
          day = 30;
          month = "SEPTEMBER";
       }
       else if(month == "NOVEMBER")
       {
          day = 31;
          month = "OCTOBER";
       }
       else if(month == "DECEMBER")
       {
          day = 30;
          month = "NOVEMBER";
       }
    }
}  
   
DayOfYear DayOfYear::operator--(int)
{
    int temp = day;
    temp--;
    if(temp == 0)
    {
      if(month == "JANUARY")
       {
          temp = 31;
          month = "DECEMBER";
       }
       else if(month == "FEBRUARY")
       {
          temp = 31;
          month = "JANUARY";
       }
       else if(month == "MARCH")
       {
          temp = 29;
          month = "FEBRUARY";
       }
       else if(month == "APRIL")
       {
          temp = 31;
          month = "MARCH";
       }
       else if(month == "MAY")
       {
          temp = 30;
          month = "APRIL";
       }
       else if(month == "JUNE")
       {
          temp = 31;
          month = "MAY";
       }
       else if(month == "JULY")
       {
          temp = 30;
          month = "JUNE";
       }
       else if(month == "AUGUST")
       {
          temp = 31;
          month = "JULY";
       }
       else if(month == "SEPTEMBER")
       {
          temp = 31;
          month = "JULY";
       }
       else if(month == "OCTOBER")
       {
          temp = 30;
          month = "SEPTEMBER";
       }
       else if(month == "NOVEMBER")
       {
          temp = 31;
          month = "OCTOBER";
       }
       else if(month == "DECEMBER")
       {
          temp = 30;
          month = "NOVEMBER";
       }
    }
}