二进制枚举子集问题

#include<iostream>
#include<algorithm>
using namespace std;
int n;
int a[]={1,2,3,4,5,6,7,8,9,10,11,12,13,14,15};
int main()
{
    ios::sync_with_stdio(false);
    cin.tie(0);
    cout.tie(0);
    cin >> n;
    for (int op = 0; op < 1 << n; op ++ )
    {
        for (int j = 0; j < n; j ++ )
        {
            if(op >> j & 1)
            {
                cout << a[j] <<" ";
            }
        }
        cout << endl; 
    } 
    return 0;
}