这段程序是怎么运行的？
#include <iostream>using namespace std;class Int{ static int addtime;public: Int(int x) {} friend int operator+(const Int &r1, const Int &r2) { return ++addtime; }};int Int::addtime = 0;int main(){ Int a(1), b(1), c(1); cout << a + a << endl; cout << b + b << endl; cout << b + c << endl; cout << c + c << endl; cout << a + a << endl;}
