自加自减运算符重载

#include <iostream>

using namespace std;

class CDemo {
private:
    int n;
public:
    CDemo(int i = 0):n(i){}
    CDemo& operator++();
    CDemo operator++(int);
    operator int() { return n; }
    friend CDemo& operator--(CDemo&);
    friend CDemo operator--(CDemo&, int);
};

CDemo& CDemo::operator++() {
    n++;
    return *this;
}

CDemo CDemo::operator++(int k) {
    CDemo tmp(*this);
    n++;
    return tmp;
}

CDemo& operator--(CDemo& d) {
    d.n--;
    return d;
}

CDemo operator--(CDemo& d, int) {
    CDemo tmp(d);
    d.n--;
    return tmp;
}

int main(){
    CDemo d(5);
    cout << (d++) << ","; //等价于 d.operator++(0);
    cout << d << ",";
    cout << (++d) << ","; //等价于 d.operator++();
    cout << d << endl;
    cout << (d--) << ","; //等价于 operator--(d,0);
    cout << d << ",";
    cout << (--d) << ","; //等价于 operator--(d);
    cout << d << endl;
    return 0;
}