Problem p03712 (C++)

Buggy submission (status: Runtime Error):
#include <bits/stdc++.h>
using ll = long long;
using namespace std;
#define rep(i, n) for (int i = 0, i##_len = (int)(n); i < i##_len; i++)
#define reps(i, n) for (int i = 1, i##_len = (int)(n); i <= i##_len; i++)
#define rrep(i, n) for (int i = ((int)(n)-1); i >= 0; i--)
#define rreps(i, n) for (int i = ((int)(n)); i > 0; i--)
#define repi(i, x)                                                             \
  for (auto i = (x).begin(), i##_fin = (x).end(); i != i##_fin; i++)
#define all(x) (x).begin(), (x).end()
#define input(array)                                                           \
  repi(array##_itr, array) { cin >> *(array##_itr); }
#define F first
#define S second
#define mp make_pair
#define mt make_tuple
#define pb push_back
#define eb emplace_back
string solve(bool a) { return ((a) ? "Yes" : "No"); }
typedef vector<int> Vi;
typedef vector<Vi> VVi;
typedef pair<int, int> Pi;
typedef vector<Pi> VPi;
typedef vector<long long> V;
typedef vector<V> VV;
typedef pair<long long, long long> P;
typedef vector<P> VP;
template <class T> inline bool chmax(T &a, T b) {
  if (a < b) {
    a = b;
    return 1;
  }
  return 0;
}
template <class T> inline bool chmin(T &a, T b) {
  if (a > b) {
    a = b;
    return 1;
  }
  return 0;
}
const long long INFLL = 1LL << 60;
const int INF = 1 << 30;
const double PI = acos(-1);
int main() {
  int h, w;
  int ans = 0;
  cin >> h >> w;
  vector<string> s(h);
  input(s);
  rep(i, w + 2) { cout << "#"; }
  cout << endl;
  rep(i, w) { cout << "#" << s[i] << "#" << endl; }
  rep(i, w + 2) { cout << "#"; }
  cout << endl;
}

Fixed submission:
#include <bits/stdc++.h>
using ll = long long;
using namespace std;
#define rep(i, n) for (int i = 0, i##_len = (int)(n); i < i##_len; i++)
#define reps(i, n) for (int i = 1, i##_len = (int)(n); i <= i##_len; i++)
#define rrep(i, n) for (int i = ((int)(n)-1); i >= 0; i--)
#define rreps(i, n) for (int i = ((int)(n)); i > 0; i--)
#define repi(i, x)                                                             \
  for (auto i = (x).begin(), i##_fin = (x).end(); i != i##_fin; i++)
#define all(x) (x).begin(), (x).end()
#define input(array)                                                           \
  repi(array##_itr, array) { cin >> *(array##_itr); }
#define F first
#define S second
#define mp make_pair
#define mt make_tuple
#define pb push_back
#define eb emplace_back
string solve(bool a) { return ((a) ? "Yes" : "No"); }
typedef vector<int> Vi;
typedef vector<Vi> VVi;
typedef pair<int, int> Pi;
typedef vector<Pi> VPi;
typedef vector<long long> V;
typedef vector<V> VV;
typedef pair<long long, long long> P;
typedef vector<P> VP;
template <class T> inline bool chmax(T &a, T b) {
  if (a < b) {
    a = b;
    return 1;
  }
  return 0;
}
template <class T> inline bool chmin(T &a, T b) {
  if (a > b) {
    a = b;
    return 1;
  }
  return 0;
}
const long long INFLL = 1LL << 60;
const int INF = 1 << 30;
const double PI = acos(-1);
int main() {
  int h, w;
  int ans = 0;
  cin >> h >> w;
  vector<string> s(h);
  input(s);
  rep(i, w + 2) { cout << "#"; }
  cout << endl;
  rep(i, h) { cout << "#" << s[i] << "#" << endl; }
  rep(i, w + 2) { cout << "#"; }
  cout << endl;
}