Problem p02801 (C++)

Buggy submission (status: Runtime Error):
#pragma GCC optimize(                                                          \
    "Ofast") // Comment optimisations for an interative problem/use endl
#pragma GCC target("avx,avx2,fma")
#pragma GCC optimization("unroll-loops")

#include <bits/stdc++.h>

using namespace std;

typedef long long ll;
typedef pair<ll, ll> pll;
typedef pair<string, string> pss;
typedef vector<pll> vpll;
typedef vector<ll> vll;
typedef vector<vll> vvll;
typedef unordered_map<ll, ll> um;

#define fastio                                                                 \
  ios::sync_with_stdio(0);                                                     \
  cin.tie(0);                                                                  \
  cout.tie(0);                                                                 \
  cout << fixed;                                                               \
  cout << setprecision(10);
#define sqr(x) ((ll)(x) * (x))
#define reset(a, b) memset(a, b, sizeof(a))
#define f first
#define s second
#define mp make_pair
#define pb push_back
#define all(v) v.begin(), v.end()
#define alla(arr, sz) arr, arr + sz
#define showv(v)                                                               \
  for (auto it : (v))                                                          \
    cout << it << " ";                                                         \
  newl;
#define newl cout << "\n"

const ll MAXN = 1e+2 + 7;
const ll MOD = 1e+9 + 7, INF = 0x7f7f7f7f7f7f7f7f;
const int INFi = 0x7f7f7f7f;
double EPS = 1e-9;
double PI = acos(-1);

vll adj[MAXN];
ll visit[MAXN] = {};
int dx8[] = {0, 1, 1, 1, 0, -1, -1, -1}, dy8[] = {1, 1, 0, -1, -1, -1, 0, 1},
    dx4[] = {0, 1, 0, -1}, dy4[] = {1, 0, -1, 0};

//<<-----Declare Variable Here------->>//
ll t, n;
ll i, j;

//<<-----Implement Functions Here---->>//

//<<-----Start of Main--------------->>//

int main() {
#ifndef ONLINE_JUDGE
  freopen("input.txt", "r", stdin);
  freopen("output.txt", "w", stdout);
#endif // ONLINE_JUDGE

  fastio;
  char c;
  cin >> c;
  cout << char(c + 1);
}

Fixed submission:
#pragma GCC optimize(                                                          \
    "Ofast") // Comment optimisations for an interative problem/use endl
#pragma GCC target("avx,avx2,fma")
#pragma GCC optimization("unroll-loops")

#include <bits/stdc++.h>

using namespace std;

typedef long long ll;
typedef pair<ll, ll> pll;
typedef pair<string, string> pss;
typedef vector<pll> vpll;
typedef vector<ll> vll;
typedef vector<vll> vvll;
typedef unordered_map<ll, ll> um;

#define fastio                                                                 \
  ios::sync_with_stdio(0);                                                     \
  cin.tie(0);                                                                  \
  cout.tie(0);                                                                 \
  cout << fixed;                                                               \
  cout << setprecision(10);
#define sqr(x) ((ll)(x) * (x))
#define reset(a, b) memset(a, b, sizeof(a))
#define f first
#define s second
#define mp make_pair
#define pb push_back
#define all(v) v.begin(), v.end()
#define alla(arr, sz) arr, arr + sz
#define showv(v)                                                               \
  for (auto it : (v))                                                          \
    cout << it << " ";                                                         \
  newl;
#define newl cout << "\n"

const ll MAXN = 1e+2 + 7;
const ll MOD = 1e+9 + 7, INF = 0x7f7f7f7f7f7f7f7f;
const int INFi = 0x7f7f7f7f;
double EPS = 1e-9;
double PI = acos(-1);

vll adj[MAXN];
ll visit[MAXN] = {};
int dx8[] = {0, 1, 1, 1, 0, -1, -1, -1}, dy8[] = {1, 1, 0, -1, -1, -1, 0, 1},
    dx4[] = {0, 1, 0, -1}, dy4[] = {1, 0, -1, 0};

//<<-----Declare Variable Here------->>//
ll t, n;
ll i, j;

//<<-----Implement Functions Here---->>//

//<<-----Start of Main--------------->>//

int main() {

  fastio;
  char c;
  cin >> c;
  cout << char(c + 1);
}