question about overloading operators in dates istream/ostream

Question

I'm currently experiencing something I'm not sure about. Here is the code

ostream& operator<<(ostream &out, Date other)
{
  out << other.month << "/" << other.day << "/" << other.year;
  return out;
}

istream& operator>>(istream &in, Date &other)
{
  char dummy;
  in >> other.month >> dummy >> other.day >> dummy >> other.year;
  return in;
}

And here it is in main

 //create an object
  Date date1(1,1,2000);
  cout << "enter a date: ";
  cin >> date1;
  cout << "Date is: " << date1 << endl;

  date1.increment();
  cout << "Date is: " << date1 << endl;

I'm getting the date and everything right, but for some reason in the day section of the date, mm/dd/yy, it is only showing the single digits number. Specifically, I get this on my compile:

enter a date: 12
10
2021
Date is: 12/0/21
Date is: 12/1/21

Here is the date.cpp file:

Date::Date()
{
    month = 1, day = 1, year = 2000;
}

//default constructor. data validation to check for month, day, years
Date::Date(int mon, int days, int yer)
{
    bool badDate = false;

    if ((mon < 0) || (mon > 12))
    {
        badDate = true;
    }
    if ((days < 0) || (days > 30))
    {
        badDate = true;
    }
    if (yer < 0)
    {
        badDate = true;
    }

    //if all data is good, default deconstructor if no parameters
    if (badDate)
    {
        month = 1;
        day = 1;
        year = 2000;
    }
    //else data in code
    else {
        month = mon;
        day = days;
        year = yer;
    }
}
ostream& operator<<(ostream &out, Date other)
{
  out << other.month << "/" << other.day << "/" << other.year;
  return out;
}

istream& operator>>(istream &in, Date &other)
{
  char dummy;
  in >> other.month >> dummy >> other.day >> dummy >> other.year;
  return in;
}