scanf와 printf 로 하면 맞는데 왜 cout으로 하면 틀리다고 나올까요?

#include <iostream>
using namespace std;
int main() {
int a=0, b=0;
cin >> a >> b;
cout << a+b << endl;
cout << a - b << endl;
cout << a + b << endl;
cout << (a / b) << endl;
cout << a%b << endl;

return 0;
}