Language: C++

#include <iostream>
#include <algorithm>
#include <cmath>
#include <map>
#include <vector>
#include <queue>
#include <functional>
#include <string>
#include <stack>

using namespace std;
using ll = long long;
typedef unsigned long long ull;
typedef pair<ll, ll> P;
typedef pair<ll, pair<ll, ll>> PP;

const ll MOD = 1e9 + 7;
const ll MOD2 = 998244353;
const ll INF = 1 << 30;
const ll INF2 = 9e18;
const double INF3 = 9e14;
const int dx[4] = { 1,0,-1,0 }, dy[4] = { 0,1,0,-1 };
const int tx[8] = { -1,0,1,-1,1,-1,0,1 }, ty[8] = { -1,-1,-1,0,0,1,1,1 };
#define ALL(x) (x).begin(),(x).end()
#define pb push_back
#define fr first
#define sc second


int main(){
	int a, b, c, n;
	string s, t;
	cin >> a;
	if (a < 1000)cout << "ABC" < endl;
	else cout << "ABD" << endl;
	return 0;
}


Compiler output:
a.cc: In function 'int main()':
a.cc:34:36: error: no match for 'operator<' (operand types are 'std::basic_ostream<char>' and '<unresolved overloaded function type>')
   34 |         if (a < 1000)cout << "ABC" < endl;
      |                      ~~~~~~~~~~~~~~^~~~~~
In file included from /usr/include/c++/14/string:48,
                 from /usr/include/c++/14/bits/locale_classes.h:40,
                 from /usr/include/c++/14/bits/ios_base.h:41,
                 from /usr/include/c++/14/ios:44,
                 from /usr/include/c++/14/ostream:40,
                 from /usr/include/c++/14/iostream:41,
                 from a.cc:1:
/usr/include/c++/14/bits/stl_iterator.h:448:5: note: candidate: 'template<class _Iterator> constexpr bool std::operator<(const reverse_iterator<_Iterator>&, const reverse_iterator<_Iterator>&)'
  448 |     operator<(const reverse_iterator<_Iterator>& __x,
      |     ^~~~~~~~
/usr/include/c++/14/bits/stl_iterator.h:448:5: note:   template argument deduction/substitution failed:
a.cc:34:38: note:   'std::basic_ostream<char>' is not derived from 'const std::reverse_iterator<_Iterator>'
   34 |         if (a < 1000)cout << "ABC" < endl;
      |                                      ^~~~
/usr/include/c++/14/bits/stl_iterator.h:493:5: note: candidate: 'template<class _IteratorL, class _IteratorR> constexpr bool std::operator<(const reverse_iterator<_Iterator>&, const reverse_iterator<_IteratorR>&)'
  493 |     operator<(const reverse_iterator<_IteratorL>& __x,
      |     ^~~~~~~~
/usr/include/c++/14/bits/stl_iterator.h:493:5: note:   template argument deduction/substitution failed:
a.cc:34:38: note:   'std::basic_ostream<char>' is not derived from 'const std::reverse_iterator<_Iterator>'
   34 |         if (a < 1000)cout << "ABC" < endl;
      |                                      ^~~~
/usr/include/c++/14/bits/stl_iterator.h:1694:5: note: candidate: 'template<class _IteratorL, class _IteratorR> constexpr bool std::operator<(const move_iterator<_IteratorL>&, const move_iterator<_IteratorR>&)'
 1694 |     operator<(const move_iterator<_IteratorL>& __x,
      |     ^~~~~~~~
/usr/include/c++/14/bits/stl_iterator.h:1694:5: note:   template argument deduction/substitution failed:
a.cc:34:38: note:   'std::basic_ostream<char>' is not derived from 'const std::move_iterator<_IteratorL>'
   34 |         if (a < 1000)cout << "ABC" < endl;
      |                                      ^~~~
/usr/include/c++/14/bits/stl_iterator.h:1760:5: note: candidate: 'template<class _Iterator> constexpr bool std::operator<(const move_iterator<_IteratorL>&, const move_iterator<_IteratorL>&)'
 1760 |     operator<(const move_iterator<_Iterator>& __x,
      |     ^~~~~~~~
/usr/include/c++/14/bits/stl_iterator.h:1760:5: note:   template argument deduction/substitution failed:
a.cc:34:38: note:   'std::basic_ostream<char>' is not derived from 'const std::move_iterator<_IteratorL>'
   34 |         if (a < 1000)cout << "ABC" < endl;
      |                                      ^~~~
In file included from /usr/include/c++/14/bits/stl_algobase.h:64,
                 from /usr/include/c++/14/string:51:
/usr/include/c++/14/bits/stl_pair.h:1045:5: note: candidate: 'template<class _T1, class _T2> constexpr bool std::operator<(const pair<_T1, _T2>&, const pair<_T1, _T2>&)'
 1045 |     operator<(const pair<_T1, _T2>& __x, const pair<_T1, _T2>& __y)
      |     ^~~~~~~~
/usr/include/c++/14/bits/stl_pair.h:1045:5: note:   template argument deduction/substitution failed:
a.cc:34:38: note:   'std::basic_ostream<char>' is not derived from 'const std::pair<_T1, _T2>'
   34 |         if (a < 1000)cout << "ABC" < endl;
      |                                      ^~~~
In file included from /usr/include/c++/14/bits/basic_string.h:47,
                 from /usr/include/c++/14/string:54:
/usr/include/c++/14/string_view:673:5: note: candidate: 'template<class _CharT, class _Traits> constexpr bool std::operator<(basic_string_view<_CharT, _Traits>, basic_string_view<_CharT, _Traits>)'
  673 |     operator< (basic_string_view<_CharT, _Traits> __x,
      |     ^~~~~~~~
/usr/include/c++/14/string_view:673:5: note:   template argument deduction/substitution failed:
a.cc:34:38: note:   'std::basic_ostream<char>' is not derived from 'std::basic_string_view<_CharT, _Traits>'
   34 |         if (a < 1000)cout << "ABC" < endl;
      |                                      ^~~~
/usr/include/c++/14/string_view:680:5: note: candidate: 'template<class _CharT, class _Traits> constexpr bool std::operator<(basic_string_view<_CharT, _Traits>, __type_identity_t<basic_string_view<_CharT, _Traits> >)'
  680 |     operator< (basic_string_view<_CharT, _Traits> __x,
      |     ^~~~~~~~
/usr/include/c++/14/string_view:680:5: note:   template argument deduction/substitution failed:
a.cc:34:38: note:   'std::basic_ostream<char>' is not derived from 'std::basic_string_view<_CharT, _Traits>'
   34 |         if (a < 1000)cout << "ABC" < endl;
      |                                      ^~~~
/usr/include/c++/14/string_view:688:5: note: candidate: 'template<class _CharT, class _Traits> constexpr bool std::operator<(__type_identity_t<basic_string_view<_CharT, _Traits> >, basic_string_view<_CharT, _Traits>)'
  688 |     operator< (__type_identity_t<basic_string_view<_CharT, _Traits>> __x,
      |     ^~~~~~~~
/usr/include/c++/14/string_view:688:5: note:   template argument deduction/substitution failed:
a.cc:34:38: note:   couldn't deduce template parameter '_CharT'
   34 |         if (a < 1000)cout << "ABC" < endl;
      |                                      ^~~~
/usr/include/c++/14/bits/basic_string.h:3874:5: note: candidate: 'template<class _CharT, class _Traits, class _Alloc> bool std::operator<(const __cxx11::basic_string<_CharT, _Traits, _Allocator>&, const __cxx11::basic_string<_CharT, _Traits, _Allocator>&)'
 3874 |     operator<(const basic_string<_CharT, _Traits, _Alloc>& __lhs,
      |     ^~~~~~~~
/usr/include/c++/14/bits/basic_string.h:3874:5: note:   template argument deduction/substitution failed:
a.cc:34:38: note:   'std::basic_ostream<char>' is not derived from 'const std::__cxx11::basic_string<_CharT, _Traits, _Allocator>'
   34 |         if (a < 1000)cout << "ABC" < endl;
      |                                      ^~~~
/usr/include/c++/14/bits/basic_string.h:3888:5: note: candidate: 'template<class _CharT, class _Traits, class _Alloc> bool std::operator<(const __cxx11::basic_string<_CharT, _Traits, _Allocator>&, const _CharT*)'
 3888 |     operator<(const basic_string<_CharT, _Traits, _Alloc>& __lhs,
      |     ^~~~~~~~
/usr/include/c++/14/bits/basic_string.h:3888:5: note:   template argument deduction/substitution failed:
a.cc:34:38: note:   'std::basic_ostream<char>' is not derived from 'const std::__cxx11::basic_string<_CharT, _Traits, _Allocator>'
   34 |         if (a < 1000)cout << "ABC" < endl;
      |                                      ^~~~
/usr/include/c++/14/bits/basic_string.h:3901:5: note: candidate: 'template<class _CharT, class _Traits, class _Alloc> bool std::operator<(const _CharT*, const __cxx11::basic_string<_CharT, _Traits, _Allocator>&)'
 3901 |     operator<(const _CharT* __lhs,
      |     ^~~~~~~~
/usr/include/c++/14/bits/basic_string.h:3901:5: note:   template argument deduction/substitution failed:
a.cc:34:38: note:   mismatched types 'const _CharT*' and 'std::basic_ostream<char>'
   34 |         if (a < 1000)cout << "ABC" < endl;
      |                                      ^~~~
In file included from /usr/include/c++/14/bits/memory_resource.h:47,
                 from /usr/include/c++/14/string:68:
/usr/include/c++/14/tuple:2600:5: note: candidate: 'template<class ... _TElements, class ... _UElements> constexpr bool std::operator<(const tuple<_UTypes ...>&, const tuple<_Elements ...>&)'
 2600 |     operator<(const tuple<_TElements...>& __t,
      |     ^~~~~~~~
/usr/include/c++/14/tuple:2600:5: note:   template argument deduction/substitution failed:
a.cc:34:38: note:   'std::basic_ostream<char>' is not derived from 'const std::tuple<_UTypes ...>'
   34 |         if (a < 1000)cout << "ABC" < endl;
      |                                      ^~~~
In file included from /usr/include/c++/14/map:63,
                 from a.cc:4:
/usr/include/c++/14/bits/stl_map.h:1550:5: note: candidate: 'template<class _Key, class _Tp, class _Compare, class _Alloc> bool std::operator<(const map<_Key, _Tp, _Compare, _Allocator>&, const map<_Key, _Tp, _Compare, _Allocator>&)'
 1550 |     operator<(const map<_Key, _Tp, _Compare, _Alloc>& __x,
      |     ^~~~~~~~
/usr/include/c++/14/bits/stl_map.h:1550:5: note:   template argument deduction/substitution failed:
a.cc:34:38: note:   'std::basic_ostream<char>' is not derived from 'const std::map<_Key, _Tp, _Compare, _Allocator>'
   34 |         if (a < 1000)cout << "ABC" < endl;
      |                                      ^~~~
In file included from /usr/include/c++/14/map:64:
/usr/include/c++/14/bits/stl_multimap.h:1172:5: note: candidate: 'template<class _Key, class _Tp, class _Compare, class _Alloc> bool std::operator<(const multimap<_Key, _Tp, _Compare, _Allocator>&, const multimap<_Key, _Tp, _Compare, _Allocator>&)'
 1172 |     operator<(const multimap<_Key, _Tp, _Compare, _Alloc>& __x,
      |     ^~~~~~~~
/usr/include/c++/14/bits/stl_multimap.h:1172:5: note:   template argument deduction/substitution failed:
a.cc:34:38: note:   'std::basic_ostream<char>' is not derived from 'const std::multimap<_Key, _Tp, _Compare, _Allocator>'
   34 |         if (a < 1000)cout << "ABC" < endl;
      |                                      ^~~~
In file included from /usr/include/c++/14/vector:66,
                 from a.cc:5:
/usr/include/c++/14/bits/stl_vector.h:2089:5: note: candidate: 'template<class _Tp, class _Alloc> bool std::operator<(const vector<_Tp, _Alloc>&, const vector<_Tp, _Alloc>&)'
 2089 |     operator<(const vector<_Tp, _Alloc>& __x, const vector<_Tp, _Alloc>& __y)
      |     ^~~~~~~~
/usr/include/c++/14/bits/stl_vector.h:2089:5: note:   template argument deduction/substitution failed:
a.cc:34:38: note:   'std::basic_ostream<char>' is not derived from 'const std::vector<_Tp, _Alloc>'
   34 |         if (a < 1000)cout << "ABC" <