Language: C++

#include <iostream>
#include <string>
using namespace std;
int comp(string& a, string& b) {
  if(a.size() < b.size()) return 0;
  if(a.size() > b.size()) return 2;
  if(a < b) return 0;
  if(a > b) return 2;
  return 1;
}

int main() {
  string a, b;
  cin >> a >> b;
  cout << {"LESS", "EQUAL", "GREATER"}[comp(a, b)] << endl;
}

Compiler output:
a.cc: In function 'int main()':
a.cc:15:11: error: expected primary-expression before '{' token
   15 |   cout << {"LESS", "EQUAL", "GREATER"}[comp(a, b)] << endl;
      |           ^
a.cc:15:49: error: expression list treated as compound expression in initializer [-fpermissive]
   15 |   cout << {"LESS", "EQUAL", "GREATER"}[comp(a, b)] << endl;
      |                                                 ^
a.cc: In lambda function:
a.cc:15:52: error: expected '{' before '<<' token
   15 |   cout << {"LESS", "EQUAL", "GREATER"}[comp(a, b)] << endl;
      |                                                    ^~
a.cc: In function 'int main()':
a.cc:15:52: error: no match for 'operator<<' (operand types are 'main()::<lambda()>' and '<unresolved overloaded function type>')
   15 |   cout << {"LESS", "EQUAL", "GREATER"}[comp(a, b)] << endl;
      |                                       ~~~~~~~~~~~~~^~~~~~~
In file included from /usr/include/c++/14/bits/basic_string.h:47,
                 from /usr/include/c++/14/string:54,
                 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/string_view:763:5: note: candidate: 'template<class _CharT, class _Traits> std::basic_ostream<_CharT, _Traits>& std::operator<<(basic_ostream<_CharT, _Traits>&, basic_string_view<_CharT, _Traits>)'
  763 |     operator<<(basic_ostream<_CharT, _Traits>& __os,
      |     ^~~~~~~~
/usr/include/c++/14/string_view:763:5: note:   template argument deduction/substitution failed:
a.cc:15:55: note:   'main()::<lambda()>' is not derived from 'std::basic_ostream<_CharT, _Traits>'
   15 |   cout << {"LESS", "EQUAL", "GREATER"}[comp(a, b)] << endl;
      |                                                       ^~~~
/usr/include/c++/14/bits/basic_string.h:4077:5: note: candidate: 'template<class _CharT, class _Traits, class _Alloc> std::basic_ostream<_CharT, _Traits>& std::operator<<(basic_ostream<_CharT, _Traits>&, const __cxx11::basic_string<_CharT, _Traits, _Allocator>&)'
 4077 |     operator<<(basic_ostream<_CharT, _Traits>& __os,
      |     ^~~~~~~~
/usr/include/c++/14/bits/basic_string.h:4077:5: note:   template argument deduction/substitution failed:
a.cc:15:55: note:   'main()::<lambda()>' is not derived from 'std::basic_ostream<_CharT, _Traits>'
   15 |   cout << {"LESS", "EQUAL", "GREATER"}[comp(a, b)] << endl;
      |                                                       ^~~~
In file included from /usr/include/c++/14/bits/memory_resource.h:38,
                 from /usr/include/c++/14/string:68:
/usr/include/c++/14/cstddef:125:5: note: candidate: 'template<class _IntegerType> constexpr std::__byte_op_t<_IntegerType> std::operator<<(byte, _IntegerType)'
  125 |     operator<<(byte __b, _IntegerType __shift) noexcept
      |     ^~~~~~~~
/usr/include/c++/14/cstddef:125:5: note:   template argument deduction/substitution failed:
a.cc:15:55: note:   couldn't deduce template parameter '_IntegerType'
   15 |   cout << {"LESS", "EQUAL", "GREATER"}[comp(a, b)] << endl;
      |                                                       ^~~~
In file included from /usr/include/c++/14/bits/ios_base.h:46:
/usr/include/c++/14/system_error:339:5: note: candidate: 'template<class _CharT, class _Traits> std::basic_ostream<_CharT, _Traits>& std::operator<<(basic_ostream<_CharT, _Traits>&, const error_code&)'
  339 |     operator<<(basic_ostream<_CharT, _Traits>& __os, const error_code& __e)
      |     ^~~~~~~~
/usr/include/c++/14/system_error:339:5: note:   template argument deduction/substitution failed:
a.cc:15:55: note:   'main()::<lambda()>' is not derived from 'std::basic_ostream<_CharT, _Traits>'
   15 |   cout << {"LESS", "EQUAL", "GREATER"}[comp(a, b)] << endl;
      |                                                       ^~~~
/usr/include/c++/14/ostream:563:5: note: candidate: 'template<class _CharT, class _Traits> std::basic_ostream<_CharT, _Traits>& std::operator<<(basic_ostream<_CharT, _Traits>&, _CharT)'
  563 |     operator<<(basic_ostream<_CharT, _Traits>& __out, _CharT __c)
      |     ^~~~~~~~
/usr/include/c++/14/ostream:563:5: note:   template argument deduction/substitution failed:
a.cc:15:55: note:   'main()::<lambda()>' is not derived from 'std::basic_ostream<_CharT, _Traits>'
   15 |   cout << {"LESS", "EQUAL", "GREATER"}[comp(a, b)] << endl;
      |                                                       ^~~~
/usr/include/c++/14/ostream:573:5: note: candidate: 'template<class _CharT, class _Traits> std::basic_ostream<_CharT, _Traits>& std::operator<<(basic_ostream<_CharT, _Traits>&, char)'
  573 |     operator<<(basic_ostream<_CharT, _Traits>& __out, char __c)
      |     ^~~~~~~~
/usr/include/c++/14/ostream:573:5: note:   template argument deduction/substitution failed:
a.cc:15:55: note:   'main()::<lambda()>' is not derived from 'std::basic_ostream<_CharT, _Traits>'
   15 |   cout << {"LESS", "EQUAL", "GREATER"}[comp(a, b)] << endl;
      |                                                       ^~~~
/usr/include/c++/14/ostream:579:5: note: candidate: 'template<class _Traits> std::basic_ostream<char, _Traits>& std::operator<<(basic_ostream<char, _Traits>&, char)'
  579 |     operator<<(basic_ostream<char, _Traits>& __out, char __c)
      |     ^~~~~~~~
/usr/include/c++/14/ostream:579:5: note:   template argument deduction/substitution failed:
a.cc:15:55: note:   'main()::<lambda()>' is not derived from 'std::basic_ostream<char, _Traits>'
   15 |   cout << {"LESS", "EQUAL", "GREATER"}[comp(a, b)] << endl;
      |                                                       ^~~~
/usr/include/c++/14/ostream:590:5: note: candidate: 'template<class _Traits> std::basic_ostream<char, _Traits>& std::operator<<(basic_ostream<char, _Traits>&, signed char)'
  590 |     operator<<(basic_ostream<char, _Traits>& __out, signed char __c)
      |     ^~~~~~~~
/usr/include/c++/14/ostream:590:5: note:   template argument deduction/substitution failed:
a.cc:15:55: note:   'main()::<lambda()>' is not derived from 'std::basic_ostream<char, _Traits>'
   15 |   cout << {"LESS", "EQUAL", "GREATER"}[comp(a, b)] << endl;
      |                                                       ^~~~
/usr/include/c++/14/ostream:595:5: note: candidate: 'template<class _Traits> std::basic_ostream<char, _Traits>& std::operator<<(basic_ostream<char, _Traits>&, unsigned char)'
  595 |     operator<<(basic_ostream<char, _Traits>& __out, unsigned char __c)
      |     ^~~~~~~~
/usr/include/c++/14/ostream:595:5: note:   template argument deduction/substitution failed:
a.cc:15:55: note:   'main()::<lambda()>' is not derived from 'std::basic_ostream<char, _Traits>'
   15 |   cout << {"LESS", "EQUAL", "GREATER"}[comp(a, b)] << endl;
      |                                                       ^~~~
/usr/include/c++/14/ostream:654:5: note: candidate: 'template<class _CharT, class _Traits> std::basic_ostream<_CharT, _Traits>& std::operator<<(basic_ostream<_CharT, _Traits>&, const _CharT*)'
  654 |     operator<<(basic_ostream<_CharT, _Traits>& __out, const _CharT* __s)
      |     ^~~~~~~~
/usr/include/c++/14/ostream:654:5: note:   template argument deduction/substitution failed:
a.cc:15:55: note:   'main()::<lambda()>' is not derived from 'std::basic_ostream<_CharT, _Traits>'
   15 |   cout << {"LESS", "EQUAL", "GREATER"}[comp(a, b)] << endl;
      |                                                       ^~~~
In file included from /usr/include/c++/14/ostream:1022:
/usr/include/c++/14/bits/ostream.tcc:307:5: note: candidate: 'template<class _CharT, class _Traits> std::basic_ostream<_CharT, _Traits>& std::operator<<(basic_ostream<_CharT, _Traits>&, const char*)'
  307 |     operator<<(basic_ostream<_CharT, _Traits>& __out, const char* __s)
      |     ^~~~~~~~
/usr/include/c++/14/bits/ostream.tcc:307:5: note:   template argument deduction/substitution failed:
a.cc:15:55: note:   'main()::<lambda()>' is not derived from 'std::basic_ostream<_CharT, _Traits>'
   15 |   cout << {"LESS", "EQUAL", "GREATER"}[comp(a, b)] << endl;
      |                                                       ^~~~
/usr/include/c++/14/ostream:671:5: note: candidate: 'template<class _Traits> std::basic_ostream<char, _Traits>& std::operator<<(basic_ostream<char, _Traits>&, const char*)'
  671 |     operator<<(basic_ostream<char, _Traits>& __out, const char* __s)
      |     ^~~~~~~~
/usr/include/c++/14/ostream:671:5: note:   template argument deduction/substitution failed:
a.cc:15:55: note:   'main()::<lambda()>' is not derived from 'std::basic_ostream<char, _Traits>'
   15 |   cout << {"LESS", "EQUAL", "GREATER"}[comp(a, b)] << endl;
      |                                                       ^~~~
/usr/include/c++/14/ostream:684:5: note: candidate: 'template<class _Traits> std::basic_ostream<char, _Traits>& std::operator<<(basic_ostream<char, _Traits>&, const signed char*)'
  684 |     operator<<(basic_ostream<char, _Traits>& __out, const signed char* __s)
      |     ^~~~~~~~
/usr/include/c++/14/ostream:684:5: note:   template argument deduction/substitution failed:
a.cc:15:55: note:   'main()::<lambda()>' is not derived from 'std::basic_ostream<char, _Traits>'
   15 |   cout << {"LESS", "EQUAL", "GREATER"}[comp(a, b)] << endl;
      |                                                       ^~~~
/usr/include/c++/14/ostream:689:5: note: candidate: 'template<class _Traits> std::basic_ostream<char, _Traits>& std::operator<<(basic_ostream<char, _Traits>&, const unsigned char*)'
  689 |     operator<<(basic_ostream<char, _Traits>& __out, const unsigned char* __s)
      |     ^~~~~~~~
/usr/include/c++/14/ostream:689:5: note:   template argument deduction/substitution failed:
a.cc:15:55: note:   'main()::<lambda()>' is not derived from 'std::basic_ostream<char, _Traits>'
   15 |   cout << {"LESS", "EQUAL", "GREATER"}[comp(a, b)] << endl;
      |                                                       ^~~~
/usr/include/c++/14/ostream:810:5: note: candidate: 'template<class _Ostream, class _Tp> _Ostream&& s