Problem p00087 (C++) — buggy submission, verdict: Runtime Error

#include <algorithm>
#include <bitset>
#include <cfloat>
#include <climits>
#include <cmath>
#include <complex>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <ctime>
#include <deque>
#include <functional>
#include <iostream>
#include <list>
#include <map>
#include <numeric>
#include <queue>
#include <set>
#include <sstream>
#include <stack>
#include <string>
#include <vector>

using namespace std;

typedef long long ll;
typedef unsigned long long ull;
typedef pair<int, int> i_i;
typedef pair<long long, int> ll_i;
typedef pair<double, int> d_i;
typedef pair<long long, long long> ll_ll;
typedef pair<double, double> d_d;

#define PI 3.141592653589793238462643383279
#define mod 1000000007LL
#define rep(i, n) for (i = 0; i < n; ++i)
#define rep1(i, n) for (i = 1; i < n; ++i)
#define rep2d(i, j, n)                                                         \\
  for (i = 0; i < n; ++i)                                                      \\
    for (j = i + 1; j < n; ++j)
#define per(i, n) for (i = n - 1; i > -1; --i)
#define int(x)                                                                 \\
  int x;                                                                       \\
  scanf("%d", &x)
#define int2(x, y)                                                             \\
  int x, y;                                                                    \\
  scanf("%d%d", &x, &y)
#define int3(x, y, z)                                                          \\
  int x, y, z;                                                                 \\
  scanf("%d%d%d", &x, &y, &z)
#define sc(x) cin >> x
#define sc2(x, y) cin >> x >> y
#define sc3(x, y, z) cin >> x >> y >> z
#define scn(n, a) rep(i, n) cin >> a[i]
#define sc2n(n, a, b) rep(i, n) cin >> a[i] >> b[i]
#define pri(x) cout << x << "\\n"
#define pri2(x, y) cout << x << " " << y << "\\n"
#define pri3(x, y, z) cout << x << " " << y << " " << z << "\\n"
#define pb push_back
#define mp make_pair
#define all(a) (a).begin(), (a).end()
#define endl "\\n"
#define kabe puts("---------------------------")
#define kara puts("")
#define debug(x) cout << " --- " << x << "\\n"
#define debug2(x, y) cout << " --- " << x << " " << y << "\\n"
#define debug3(x, y, z) cout << " --- " << x << " " << y << " " << z << "\\n"
#define X first
#define Y second
#define eps 0.0001
#define prid(x) printf("%.12lf\\n", x)

signed main(void) {
  int i, j, k;
  string s;
  for (int testcase = 0; getline(cin, s); testcase++) {
    int head = 0;
    double stc[80] = {0.0};
    s += " ";
    for (i = 0; i < s.size(); ++i) {
      if (s[i] == ' ')
        continue;
      else if (s[i] == '+') {
        head--;
        stc[head - 1] = stc[head - 1] + stc[head];
        i++;
      } else if (s[i] == '-') {
        if (s[i + 1] != ' ') {
          double sum = 0.0;
          for (i++; i < s.size(); i++) {
            if (s[i] == ' ')
              break;
            sum *= 10.0;
            sum += (double)(s[i] - '0');
          }
          stc[head++] = -sum;
        } else {
          head--;
          stc[head - 1] = stc[head - 1] - stc[head];
          i++;
        }
      } else if (s[i] == '*') {
        head--;
        stc[head - 1] = stc[head - 1] * stc[head];
        i++;
      } else if (s[i] == '/') {
        head--;
        stc[head - 1] = stc[head - 1] / stc[head];
        i++;
      } else {
        double sum = 0.0;
        for (; i < s.size(); i++) {
          if (s[i] == ' ')
            break;
          sum *= 10.0;
          sum += (double)(s[i] - '0');
        }
        stc[head++] = sum;
      }
    }
    prid(stc[0]);
    s.clear();
  }
  return 0;
}

Error: -11

Fixed submission:

#include <algorithm>
#include <bitset>
#include <cfloat>
#include <climits>
#include <cmath>
#include <complex>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <ctime>
#include <deque>
#include <functional>
#include <iostream>
#include <list>
#include <map>
#include <numeric>
#include <queue>
#include <set>
#include <sstream>
#include <stack>
#include <string>
#include <vector>

using namespace std;

typedef long long ll;
typedef unsigned long long ull;
typedef pair<int, int> i_i;
typedef pair<long long, int> ll_i;
typedef pair<double, int> d_i;
typedef pair<long long, long long> ll_ll;
typedef pair<double, double> d_d;

#define PI 3.141592653589793238462643383279
#define mod 1000000007LL
#define rep(i, n) for (i = 0; i < n; ++i)
#define rep1(i, n) for (i = 1; i < n; ++i)
#define rep2d(i, j, n)                                                         \\
  for (i = 0; i < n; ++i)                                                      \\
    for (j = i + 1; j < n; ++j)
#define per(i, n) for (i = n - 1; i > -1; --i)
#define int(x)                                                                 \\
  int x;                                                                       \\
  scanf("%d", &x)
#define int2(x, y)                                                             \\
  int x, y;                                                                    \\
  scanf("%d%d", &x, &y)
#define int3(x, y, z)                                                          \\
  int x, y, z;                                                                 \\
  scanf("%d%d%d", &x, &y, &z)
#define sc(x) cin >> x
#define sc2(x, y) cin >> x >> y
#define sc3(x, y, z) cin >> x >> y >> z
#define scn(n, a) rep(i, n) cin >> a[i]
#define sc2n(n, a, b) rep(i, n) cin >> a[i] >> b[i]
#define pri(x) cout << x << "\\n"
#define pri2(x, y) cout << x << " " << y << "\\n"
#define pri3(x, y, z) cout << x << " " << y << " " << z << "\\n"
#define pb push_back
#define mp make_pair
#define all(a) (a).begin(), (a).end()
#define endl "\\n"
#define kabe puts("---------------------------")
#define kara puts("")
#define debug(x) cout << " --- " << x << "\\n"
#define debug2(x, y) cout << " --- " << x << " " << y << "\\n"
#define debug3(x, y, z) cout << " --- " << x << " " << y << " " << z << "\\n"
#define X first
#define Y second
#define eps 0.0001
#define prid(x) printf("%.6lf\\n", x)

signed main(void) {
  int i, j, k;
  string s;
  for (int testcase = 0; getline(cin, s); testcase++) {
    int head = 0;
    double stc[80] = {0.0};
    for (i = 0; i < s.size(); ++i) {
      if (s[i] == ' ')
        continue;
      else if (s[i] == '+') {
        head--;
        stc[head - 1] = stc[head - 1] + stc[head];
        i++;
      } else if (s[i] == '-') {
        head--;
        stc[head - 1] = stc[head - 1] - stc[head];
        i++;
      } else if (s[i] == '*') {
        head--;
        stc[head - 1] = stc[head - 1] * stc[head];
        i++;
      } else if (s[i] == '/') {
        head--;
        stc[head - 1] = stc[head - 1] / stc[head];
        i++;
      } else {
        double sum = 0.0;
        for (; i < s.size(); i++) {
          if (s[i] == ' ')
            break;
          sum *= 10.0;
          sum += (double)(s[i] - '0');
        }
        stc[head++] = sum;
      }
    }
    prid(stc[0]);
    s.clear();
  }
  return 0;
}