C++ 실습 inheritance operator function quiz

#include <iostream>
#include <string>
using namespace std;
 
class A {
    int a;
public:
    A(int aa = 0):a(aa){}
    void setA(int a) { this->a = a; }
    int getA()const { return a; }
    
    friend ostream& operator<<(ostream &out, A &aa);
    friend istream& operator>>(istream &in, A &aa);
};
 
ostream& operator<<(ostream &out, A &aa) { //반복적으로 사용할수 있게 래퍼런스로 사용
    cout << aa.a;
    return out;
}
 
istream& operator>>(istream &in, A &aa) {
        cin >> aa.a;
        return in;
    }    
 
void main() {
    A aa(100);
    A bb;
    //cout << aa
    //cout << bb;
     
    cout << aa << bb;
    cin >> aa >> bb;
}