C++学习30 重载++和--（自增自减运算符）

#include <iostream>
#include <iomanip>
using namespace std;
class stopwatch{  //秒表
private:
    int min;  //分钟
    int sec;  //秒钟
public:
    stopwatch(): min(0), sec(0){ }
    void setzero(){ min = 0; sec = 0; }
    stopwatch run();  // 运行
    stopwatch operator++();  //++i，前置形式
    stopwatch operator++(int);  //i++，后置形式
    friend ostream & operator<<( ostream &, const stopwatch &);
};
stopwatch stopwatch::run(){
    ++ sec;
    if( sec == 60 ){
        min ++;
        sec = 0;
    }
    return *this;
}
stopwatch stopwatch::operator++(){
    return run();
}
stopwatch stopwatch::operator++(int n){
    stopwatch s = *this;
    run();
    return s;
}
ostream & operator<<( ostream & out, const stopwatch & s){
    out<<setfill(‘0‘)<<setw(2)<<s.min<<":"<<setw(2)<<s.sec;
    return out;
}
int main(){
    stopwatch s1, s2;
    s1 = s2 ++;
    cout << "s1: "<< s1 <<endl;
    cout << "s2: "<< s2 <<endl;
    s1.setzero();
    s2.setzero();
    s1 = ++ s2;
    cout << "s1: "<< s1 <<endl;
    cout << "s2: "<< s2 <<endl;
    return 0;
}