【求助】 C++ 运算符重载

#include<iostream>
using namespace std;
class Date
{
    private:
    int year;
    int month;
    int day;
    public:
    Date(int y=0,int m=0,int d=0)
    {
        year=y;
        month=m;
        day=d;
    }
    void display()
    {
        cout<<year<<"年"<<month<<"月"<<day<<"日"<<endl;
    }
    friend Date operator + (Date A,int a)
    {
        return Date(A.year+a,A.month,A.day);
    }
};
int main()
{
    Date A(2000,11,11),B;
    int a=11;
    cout<<"A=",  A.display();
    B=A+a;
    cout<<"B=A+a=",  B.display();
    return 0;
}