Language: C++

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

#define int long long
#define REP(i, l, r) for (int i=(l); i<(r); ++i)
#define RREP(i, r, l) for (int i=(r); i>(l); --i)
#define CASET int _T; cin >> _T; REP(caset, 0, _T)
#define print(x) cout << to_string(x) << '\n'
#define vi vector<int>
#define vb vector<bool>
#define vs vector<string>
#define pii pair<int,int>
#define t3i tuple<int,int,int>
#define mii map<int,int>
#define sq(x) (x)*(x)
#define inv(x) powa(x, MOD-2)

int INF = 1LL<<60;
int MOD = 998244353;

string to_string(string &s) {return s;}
string to_string(const char s[]) {return (string)s;}
template <class C> string to_string(C &v) {
    string res;
    for (auto &x : v) res += to_string(x) + ' ';
    return res;
}
template <typename A> istream &operator>>(istream &is, vector<A> &v) {
    for (auto &x : v) is >> x;
    return is;
}
template <typename A, typename B> ostream &operator<<(ostream &os, pair<A, B> pr) {
    os << '(' << pr.first << ", " << pr.second << ')';
    return os;
}
ostream &operator<<(ostream &os, string &s) {for (char &c : s) os << (char)c; return os;}
ostream &operator<<(ostream &os, const char s[]) {os << (string)s; return os;}
template <class C> ostream &operator<<(ostream &os, C &v) {
    bool first = true;
    os << '[';
    for (auto &x : v) {
        if (!first) os << ", ";
        first = false;
        os << x;
    }
    os << ']';
    return os;
}
string bin_string(int x) {
    const int d = 32;
    string res(d, ' ');
    REP(i, 0, d) res[d-1-i] = '0'+(x>>i & 1LL);
    return res;
}
int powa(int base, int exp) {
    int res = 1;
    while (exp) {
        if (exp&1) res = res*base % MOD;
        base = base*base % MOD;
        exp >>= 1;
    }
    return res;
}

main() {
    ios::sync_with_stdio(0), cin.tie(0), cout.tie(0);
    
    char x;
    cin >> x;
    cout << ++x;
}

Compiler output:
a.cc:65:1: warning: ISO C++ forbids declaration of 'main' with no type [-Wreturn-type]
   65 | main() {
      | ^~~~
a.cc: In function 'int main()':
a.cc:70:10: error: ambiguous overload for 'operator<<' (operand types are 'std::ostream' {aka 'std::basic_ostream<char>'} and 'char')
   70 |     cout << ++x;
      |     ~~~~ ^~ ~~~
      |     |       |
      |     |       char
      |     std::ostream {aka std::basic_ostream<char>}
In file included from /usr/include/c++/14/istream:41,
                 from /usr/include/c++/14/sstream:40,
                 from /usr/include/c++/14/complex:45,
                 from /usr/include/c++/14/ccomplex:39,
                 from /usr/include/x86_64-linux-gnu/c++/14/bits/stdc++.h:127,
                 from a.cc:1:
/usr/include/c++/14/ostream:174:7: note: candidate: 'std::basic_ostream<_CharT, _Traits>::__ostream_type& std::basic_ostream<_CharT, _Traits>::operator<<(long int) [with _CharT = char; _Traits = std::char_traits<char>; __ostream_type = std::basic_ostream<char>]'
  174 |       operator<<(long __n)
      |       ^~~~~~~~
/usr/include/c++/14/ostream:178:7: note: candidate: 'std::basic_ostream<_CharT, _Traits>::__ostream_type& std::basic_ostream<_CharT, _Traits>::operator<<(long unsigned int) [with _CharT = char; _Traits = std::char_traits<char>; __ostream_type = std::basic_ostream<char>]'
  178 |       operator<<(unsigned long __n)
      |       ^~~~~~~~
/usr/include/c++/14/ostream:182:7: note: candidate: 'std::basic_ostream<_CharT, _Traits>::__ostream_type& std::basic_ostream<_CharT, _Traits>::operator<<(bool) [with _CharT = char; _Traits = std::char_traits<char>; __ostream_type = std::basic_ostream<char>]'
  182 |       operator<<(bool __n)
      |       ^~~~~~~~
In file included from /usr/include/c++/14/ostream:1022:
/usr/include/c++/14/bits/ostream.tcc:96:5: note: candidate: 'std::basic_ostream<_CharT, _Traits>& std::basic_ostream<_CharT, _Traits>::operator<<(short int) [with _CharT = char; _Traits = std::char_traits<char>]'
   96 |     basic_ostream<_CharT, _Traits>::
      |     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/usr/include/c++/14/ostream:189:7: note: candidate: 'std::basic_ostream<_CharT, _Traits>::__ostream_type& std::basic_ostream<_CharT, _Traits>::operator<<(short unsigned int) [with _CharT = char; _Traits = std::char_traits<char>; __ostream_type = std::basic_ostream<char>]'
  189 |       operator<<(unsigned short __n)
      |       ^~~~~~~~
/usr/include/c++/14/bits/ostream.tcc:110:5: note: candidate: 'std::basic_ostream<_CharT, _Traits>& std::basic_ostream<_CharT, _Traits>::operator<<(int) [with _CharT = char; _Traits = std::char_traits<char>]'
  110 |     basic_ostream<_CharT, _Traits>::
      |     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/usr/include/c++/14/ostream:200:7: note: candidate: 'std::basic_ostream<_CharT, _Traits>::__ostream_type& std::basic_ostream<_CharT, _Traits>::operator<<(unsigned int) [with _CharT = char; _Traits = std::char_traits<char>; __ostream_type = std::basic_ostream<char>]'
  200 |       operator<<(unsigned int __n)
      |       ^~~~~~~~
/usr/include/c++/14/ostream:211:7: note: candidate: 'std::basic_ostream<_CharT, _Traits>::__ostream_type& std::basic_ostream<_CharT, _Traits>::operator<<(long long int) [with _CharT = char; _Traits = std::char_traits<char>; __ostream_type = std::basic_ostream<char>]'
  211 |       operator<<(long long __n)
      |       ^~~~~~~~
/usr/include/c++/14/ostream:215:7: note: candidate: 'std::basic_ostream<_CharT, _Traits>::__ostream_type& std::basic_ostream<_CharT, _Traits>::operator<<(long long unsigned int) [with _CharT = char; _Traits = std::char_traits<char>; __ostream_type = std::basic_ostream<char>]'
  215 |       operator<<(unsigned long long __n)
      |       ^~~~~~~~
/usr/include/c++/14/ostream:231:7: note: candidate: 'std::basic_ostream<_CharT, _Traits>::__ostream_type& std::basic_ostream<_CharT, _Traits>::operator<<(double) [with _CharT = char; _Traits = std::char_traits<char>; __ostream_type = std::basic_ostream<char>]'
  231 |       operator<<(double __f)
      |       ^~~~~~~~
/usr/include/c++/14/ostream:235:7: note: candidate: 'std::basic_ostream<_CharT, _Traits>::__ostream_type& std::basic_ostream<_CharT, _Traits>::operator<<(float) [with _CharT = char; _Traits = std::char_traits<char>; __ostream_type = std::basic_ostream<char>]'
  235 |       operator<<(float __f)
      |       ^~~~~~~~
/usr/include/c++/14/ostream:243:7: note: candidate: 'std::basic_ostream<_CharT, _Traits>::__ostream_type& std::basic_ostream<_CharT, _Traits>::operator<<(long double) [with _CharT = char; _Traits = std::char_traits<char>; __ostream_type = std::basic_ostream<char>]'
  243 |       operator<<(long double __f)
      |       ^~~~~~~~
a.cc:38:29: note: candidate: 'std::ostream& operator<<(std::ostream&, C&) [with C = char; std::ostream = std::basic_ostream<char>]'
   38 | template <class C> ostream &operator<<(ostream &os, C &v) {
      |                             ^~~~~~~~
/usr/include/c++/14/ostream:563:5: note: candidate: 'std::basic_ostream<_CharT, _Traits>& std::operator<<(basic_ostream<_CharT, _Traits>&, _CharT) [with _CharT = char; _Traits = char_traits<char>]'
  563 |     operator<<(basic_ostream<_CharT, _Traits>& __out, _CharT __c)
      |     ^~~~~~~~
/usr/include/c++/14/ostream:573:5: note: candidate: 'std::basic_ostream<_CharT, _Traits>& std::operator<<(basic_ostream<_CharT, _Traits>&, char) [with _CharT = char; _Traits = char_traits<char>]'
  573 |     operator<<(basic_ostream<_CharT, _Traits>& __out, char __c)
      |     ^~~~~~~~
/usr/include/c++/14/ostream:579:5: note: candidate: 'std::basic_ostream<char, _Traits>& std::operator<<(basic_ostream<char, _Traits>&, char) [with _Traits = char_traits<char>]'
  579 |     operator<<(basic_ostream<char, _Traits>& __out, char __c)
      |     ^~~~~~~~
/usr/include/c++/14/ostream:590:5: note: candidate: 'std::basic_ostream<char, _Traits>& std::operator<<(basic_ostream<char, _Traits>&, signed char) [with _Traits = char_traits<char>]'
  590 |     operator<<(basic_ostream<char, _Traits>& __out, signed char __c)
      |     ^~~~~~~~
/usr/include/c++/14/ostream:595:5: note: candidate: 'std::basic_ostream<char, _Traits>& std::operator<<(basic_ostream<char, _Traits>&, unsigned char) [with _Traits = char_traits<char>]'
  595 |     operator<<(basic_ostream<char, _Traits>& __out, unsigned char __c)
      |     ^~~~~~~~