输出一个数的第i位

#include <iostream>
#include<vector>
#include<algorithm>
using namespace std;
void f(vector<int>&s) {

    int a, b;
    cin >> a;
    while (a != 0)
    {
        b = a % 10;
        a = a / 10;
        s.push_back(b);
    }
}
int main()
{
    vector<int>s;
    f(s);
reverse(s.begin(),s.end());
    int n;
    cin >> n;
    cout << s[n-1];
    return 0;
}