这是什么原理

程序输出：

-2147483648

-2147482648

3

3

---

#include <bits/stdc++.h>
using namespace std;
#define ll long long
int main(){
	int a = -1;
	cout << (7 << a) << endl;
	const int aa = a;
	cout << (7 << aa) << endl;
	const int bb = -1;
	cout << (7 << bb) << endl;
	cout << (7 << -1);
	return 0;
}