Problem p00104 (C++) — buggy submission, verdict: Runtime Error

#include <algorithm>
#include <cfloat>
#include <climits>
#include <cmath>
#include <complex>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <fstream>
#include <functional>
#include <iostream>
#include <map>
#include <memory>
#include <queue>
#include <set>
#include <sstream>
#include <stack>
#include <string>
#include <utility>
#include <vector>

using namespace std;
typedef long long LL;
typedef pair<int, int> P;
static const double EPS = 1e-5;

#define FOR(i, k, n) for (int i = (k); i < (int)(n); ++i)
#define REP(i, n) FOR(i, 0, n)
bool ariv[101][101];
P end(vector<string> grid, int x, int y) {
  if (ariv[y][x])
    return P(-1, -1);
  else
    ariv[y][x] = true;
  if (grid[y][x] == '.')
    return P(x, y);
  if (grid[y][x] == '>')
    return end(grid, x + 1, y);
  if (grid[y][x] == '<')
    return end(grid, x - 1, y);
  if (grid[y][x] == '^')
    return end(grid, x, y - 1);
  if (grid[y][x] == 'v')
    return end(grid, x, y + 1);
}
void outp(vector<string> grid, int x, int y) {
  P point = end(grid, x, y);
  if (point.first == -1)
    cout << "LOOP" << endl;
  else
    printf("%d %d\\n", point.first, point.second);
}
int main(void) {
  int H, W;
  while (cin >> H >> W) {
    if (H == 0)
      break;
    vector<string> grid;
    memset(ariv, 0, sizeof(ariv));
    REP(y, H) {
      string tmp;
      cin >> tmp;
      grid.push_back(tmp);
    }
    if (grid[0][0] == '.')
      printf("0 0\\n");
    else if (grid[0][0] == '>')
      outp(grid, 1, 0);
    else if (grid[0][0] == '<')
      outp(grid, 0, 0);
    else if (grid[0][0] == '^')
      outp(grid, 0, 0);
    else if (grid[0][0] == 'v')
      outp(grid, 0, 1);
  }
  return 0;
}

Error: WA

Fixed submission:

#include <algorithm>
#include <cfloat>
#include <climits>
#include <cmath>
#include <complex>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <fstream>
#include <functional>
#include <iostream>
#include <map>
#include <memory>
#include <queue>
#include <set>
#include <sstream>
#include <stack>
#include <string>
#include <utility>
#include <vector>

using namespace std;
typedef long long LL;
typedef pair<int, int> P;
static const double EPS = 1e-5;

#define FOR(i, k, n) for (int i = (k); i < (int)(n); ++i)
#define REP(i, n) FOR(i, 0, n)
bool ariv[101][101];
P end(vector<string> grid, int x, int y) {
  if (ariv[y][x])
    return P(-1, -1);
  else
    ariv[y][x] = true;
  if (grid[y][x] == '.')
    return P(x, y);
  if (grid[y][x] == '>')
    return end(grid, x + 1, y);
  if (grid[y][x] == '<')
    return end(grid, x - 1, y);
  if (grid[y][x] == '^')
    return end(grid, x, y - 1);
  if (grid[y][x] == 'v')
    return end(grid, x, y + 1);
}
void outp(vector<string> grid, int x, int y) {
  P point = end(grid, x, y);
  if (point.first == -1)
    cout << "LOOP" << endl;
  else
    printf("%d %d\\n", point.first, point.second);
}
int main(void) {
  int H, W;
  while (cin >> H >> W) {
    vector<string> grid;
    memset(ariv, 0, sizeof(ariv));
    REP(y, H) {
      string tmp;
      cin >> tmp;
      grid.push_back(tmp);
    }
    if (grid[0][0] == '.')
      printf("0 0\\n");
    else if (grid[0][0] == '>')
      outp(grid, 1, 0);
    else if (grid[0][0] == '<')
      outp(grid, 0, 0);
    else if (grid[0][0] == '^')
      outp(grid, 0, 0);
    else if (grid[0][0] == 'v')
      outp(grid, 0, 1);
  }
  return 0;
}