Problem p00461 (C++) — buggy submission, verdict: Runtime Error

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

// define-----------------------------------------------------------------------------------------------------------------------
#define rep(i, n) for (int i = 0; i < (int)n; i++)
#define FOR(i, s, n) for (int i = s; i < (int)n; i++)
#define per(i, n) for (int i = n; i >= 0; i--)
#define ROF(i, s, n) for (int i = s; i >= (int)n; i--)
#define FORIT(i, A) for (auto i : A)
#define PRINT(x) cout << (x) << "\\n"
#define ALL(a) (a).begin(), (a).end()
#define RALL(a) (a).rbegin(), (a).rend()
#define MP make_pair
#define EACH(i, n)                                                             \\
  for (__typeof((n).begin()) i = (n).begin(); i != (n).end(); ++i)
#define SZ(a) int((a).size())
#define EXIST(s, e) ((s).find(e) != (s).end())
#define SORT(c) sort((c).begin(), (c).end())
#define CLR(a) memset((a), 0, sizeof(a))
#define dump(x) cout << #x << " = " << (x) << "\\n";
#define debug(x)                                                               \\
  cout << #x << " = " << (x) << " (L" << __LINE__ << ")"                       \\
       << " " << __FILE__ << "\\n";
#define sq(n) (n) * (n)

// typedef----------------------------------------------------------------------------------------------------------------------
typedef vector<int> VI;
typedef vector<VI> VVI;
typedef vector<string> VS;
typedef pair<int, int> PII;
typedef long long LL;
typedef vector<LL> VLL;
typedef vector<VLL> VVLL;
typedef unsigned int uint;
typedef unsigned long long ull;
typedef priority_queue<int> maxpq;
typedef priority_queue<int, vector<int>, greater<int>> minpq;
// const------------------------------------------------------------------------------------------------------------------------
static const double EPS = 1e-10;
static const double PI = acos(-1.0);
static const int mod = 1000000007;
static const int INF = 1 << 25;
static const LL LL_INF = 1152921504606846976;
// global-----------------------------------------------------------------------------------------------------------------------
string s, str;
char b[1000000];
int ans, n, d;
// #define DEBUG
// function-------------------------------------------------------------------------------------------------------------------
int main() {
  while (scanf("%d", &n) != EOF && n) {
    s = "I";
    scanf("%d", &d);
    rep(i, n) { s += "OI"; }
    ans = 0;
    scanf("%s", b);
    str = (string)b;

    rep(i, str.size() - s.size()) {
      if (str.substr(i, s.size()) == s) {
        ans++;
      }
      /*if ( str[ i ] == 'I' ) {
              i++;
      }*/
    }
    printf("%d\\n", ans);
  }
  return 0;
}

Error: 0

Fixed submission:

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

// define-----------------------------------------------------------------------------------------------------------------------
#define rep(i, n) for (int i = 0; i < (int)n; i++)
#define FOR(i, s, n) for (int i = s; i < (int)n; i++)
#define per(i, n) for (int i = n; i >= 0; i--)
#define ROF(i, s, n) for (int i = s; i >= (int)n; i--)
#define FORIT(i, A) for (auto i : A)
#define PRINT(x) cout << (x) << "\\n"
#define ALL(a) (a).begin(), (a).end()
#define RALL(a) (a).rbegin(), (a).rend()
#define MP make_pair
#define EACH(i, n)                                                             \\
  for (__typeof((n).begin()) i = (n).begin(); i != (n).end(); ++i)
#define SZ(a) int((a).size())
#define EXIST(s, e) ((s).find(e) != (s).end())
#define SORT(c) sort((c).begin(), (c).end())
#define CLR(a) memset((a), 0, sizeof(a))
#define dump(x) cout << #x << " = " << (x) << "\\n";
#define debug(x)                                                               \\
  cout << #x << " = " << (x) << " (L" << __LINE__ << ")"                       \\
       << " " << __FILE__ << "\\n";
#define sq(n) (n) * (n)

// typedef----------------------------------------------------------------------------------------------------------------------
typedef vector<int> VI;
typedef vector<VI> VVI;
typedef vector<string> VS;
typedef pair<int, int> PII;
typedef long long LL;
typedef vector<LL> VLL;
typedef vector<VLL> VVLL;
typedef unsigned int uint;
typedef unsigned long long ull;
typedef priority_queue<int> maxpq;
typedef priority_queue<int, vector<int>, greater<int>> minpq;
// const------------------------------------------------------------------------------------------------------------------------
static const double EPS = 1e-10;
static const double PI = acos(-1.0);
static const int mod = 1000000007;
static const int INF = 1 << 25;
static const LL LL_INF = 1152921504606846976;
// global-----------------------------------------------------------------------------------------------------------------------
string s, str;
char b[1000000];
int ans, n, d;
// #define DEBUG
// function-------------------------------------------------------------------------------------------------------------------
int main() {
  while (scanf("%d", &n) != EOF && n) {
    s = "I";
    scanf("%d", &d);
    rep(i, n) { s = s + "OI"; }
    ans = 0;
    scanf("%s", b);
    str = (string)b;
    rep(i, str.size() - s.size()) {
      if (str.substr(i, s.size()) == s) {
        ans++;
      }
    }
    printf("%d\\n", ans);
  }
  return 0;
}