c++ 7.11

#include<iostream.h>class Date{public:Date(){}Date(int y,int m,int d){month=m; day=d; year=y;} void print() {cout<<year<<"."<<month<<"."<<day<<endl; }  friend Date operator +(Date &op);private:int month,day,year;};Date operator+(Date &op){++op.day;    return op;}int main(){Date d1(2014,5,17);cout<<"改变日期前:";d1.print();cout<<"天数加1后:";operator +(d1);d1.print();return 0;}