Problem p01538 (C++) — buggy submission, verdict: Runtime Error

#include <bits/stdc++.h>
using namespace std;

#define iota(i, n, b, s)                                                       \\
  for (int i = int(b); i != int((b) + (s) * (n)); i += (s))
#define range(i, n, m)                                                         \\
  iota(i, (((n) > (m)) ? ((n) - (m)) : ((m) - (n))), (n), ((n) > (m) ? -1 : 1))
#define rep(i, n) iota(i, (n), 0, 1)
#define loop for (;;)

#define INF (1e9)
#define EPS (1e-9)
#define cons(a, b) (make_pair(a, b))
#define car(a) (a.first)
#define cdr(a) (a.second)
#define cadr(a) (car(cdr(a)))
#define cddr(a) (cdr(cdr(a)))
#define all(a) a.begin(), a.end()
#define trace(var) cerr << ">>> " << #var << " = " << var << endl;

typedef long long Integer;
typedef double Real;
typedef vector<int> vi;
typedef vector<string> vs;
typedef map<string, int> Dictionary;
const Real PI = acos(-1);

template <class S, class T> ostream &operator<<(ostream &os, pair<S, T> p) {
  os << '(' << car(p) << ", " << cdr(p) << ')';
  return os;
}

template <class T> ostream &operator<<(ostream &os, vector<T> v) {
  if (v.size() == 0) {
    os << "(empty)";
    return os;
  }
  os << v[0];
  for (int i = 1, len = v.size(); i < len; ++i)
    os << ' ' << v[i];
  return os;
}

int dx[] = {-1, 0, 1, 0};
int dy[] = {0, -1, 0, 1};

bool contains(vector<int> &vs, int x) {
  for (int v : vs) {
    if (v == x)
      return true;
  }
  return false;
}

int main() {

  int n;
  cin >> n;
  while (n--) {
    int x;
    cin >> x;
    int cx = 0;
    vector<int> history;

    while (x > 9) {
      int nx = 0;
      for (int d = 10;; d *= 10) {
        int z = x / d;
        int y = x % d;
        if (z == 0)
          break;
        nx = max(nx, z * y);
      }
      x = nx;
      ++cx;
    }

    cout << cx << endl;
  }

  return 0;
}

Error: 0
>>> x = 81
>>> x = 8
>>> x = 36
>>> x = 18
>>> x = 8


Fixed submission:

#include <bits/stdc++.h>
using namespace std;

#define iota(i, n, b, s)                                                       \\
  for (int i = int(b); i != int((b) + (s) * (n)); i += (s))
#define range(i, n, m)                                                         \\
  iota(i, (((n) > (m)) ? ((n) - (m)) : ((m) - (n))), (n), ((n) > (m) ? -1 : 1))
#define rep(i, n) iota(i, (n), 0, 1)
#define loop for (;;)

#define INF (1e9)
#define EPS (1e-9)
#define cons(a, b) (make_pair(a, b))
#define car(a) (a.first)
#define cdr(a) (a.second)
#define cadr(a) (car(cdr(a)))
#define cddr(a) (cdr(cdr(a)))
#define all(a) a.begin(), a.end()
#define trace(var) cerr << ">>> " << #var << " = " << var << endl;

typedef long long Integer;
typedef double Real;
typedef vector<int> vi;
typedef vector<string> vs;
typedef map<string, int> Dictionary;
const Real PI = acos(-1);

template <class S, class T> ostream &operator<<(ostream &os, pair<S, T> p) {
  os << '(' << car(p) << ", " << cdr(p) << ')';
  return os;
}

template <class T> ostream &operator<<(ostream &os, vector<T> v) {
  if (v.size() == 0) {
    os << "(empty)";
    return os;
  }
  os << v[0];
  for (int i = 1, len = v.size(); i < len; ++i)
    os << ' ' << v[i];
  return os;
}

int dx[] = {-1, 0, 1, 0};
int dy[] = {0, -1, 0, 1};

bool contains(vector<int> &vs, int x) {
  for (int v : vs) {
    if (v == x)
      return true;
  }
  return false;
}

int main() {

  int n;
  cin >> n;
  while (n--) {
    int x;
    cin >> x;
    int cx = 0;
    vector<int> history;

    while (x > 9) {
      int nx = 0;
      for (int d = 10;; d *= 10) {
        int z = x / d;
        int y = x % d;
        if (z == 0)
          break;
        nx = max(nx, z * y);
      }
      x = nx;
      trace(x);
      ++cx;
    }

    cout << cx << endl;
  }

  return 0;
}