Language: C++

#include <complex>
#include <cmath>
#include <iostream>
using namespace std;
typedef complex<double> xy_t;
xy_t P[110], a, b, c;

double cross_product(xy_t a,xy_t b) {
  return (conj(a)*b).imag()/2.0;
}

int main () {
  int N=0; //??????????????????????????°???N??¨??????
  double x, y;
  while (cin>x && cin>y) {
    P[N++] = xy_t(x,y);
  }
  //??¢????¨????
  double sum = 0.0;
  for (int i=0; i+2<N; ++i) {
    xy_t b=P[i+1], c=P[i+2];
    sum += cross_product(b, c);
  }
  cout << abs(sum) <<endl;
}

Compiler output:
a.cc: In function 'int main()':
a.cc:15:13: error: no match for 'operator>' (operand types are 'std::istream' {aka 'std::basic_istream<char>'} and 'double')
   15 |   while (cin>x && cin>y) {
      |          ~~~^~
      |          |   |
      |          |   double
      |          std::istream {aka std::basic_istream<char>}
a.cc:15:13: note: candidate: 'operator>(int, double)' (built-in)
   15 |   while (cin>x && cin>y) {
      |          ~~~^~
a.cc:15:13: note:   no known conversion for argument 1 from 'std::istream' {aka 'std::basic_istream<char>'} to 'int'
In file included from /usr/include/c++/14/bits/stl_algobase.h:64,
                 from /usr/include/c++/14/bits/specfun.h:43,
                 from /usr/include/c++/14/cmath:3906,
                 from /usr/include/c++/14/complex:44,
                 from a.cc:1:
/usr/include/c++/14/bits/stl_pair.h:1058:5: note: candidate: 'template<class _T1, class _T2> constexpr bool std::operator>(const pair<_T1, _T2>&, const pair<_T1, _T2>&)'
 1058 |     operator>(const pair<_T1, _T2>& __x, const pair<_T1, _T2>& __y)
      |     ^~~~~~~~
/usr/include/c++/14/bits/stl_pair.h:1058:5: note:   template argument deduction/substitution failed:
a.cc:15:14: note:   'std::istream' {aka 'std::basic_istream<char>'} is not derived from 'const std::pair<_T1, _T2>'
   15 |   while (cin>x && cin>y) {
      |              ^
In file included from /usr/include/c++/14/bits/stl_algobase.h:67:
/usr/include/c++/14/bits/stl_iterator.h:462:5: note: candidate: 'template<class _Iterator> constexpr bool std::operator>(const reverse_iterator<_Iterator>&, const reverse_iterator<_Iterator>&)'
  462 |     operator>(const reverse_iterator<_Iterator>& __x,
      |     ^~~~~~~~
/usr/include/c++/14/bits/stl_iterator.h:462:5: note:   template argument deduction/substitution failed:
a.cc:15:14: note:   'std::istream' {aka 'std::basic_istream<char>'} is not derived from 'const std::reverse_iterator<_Iterator>'
   15 |   while (cin>x && cin>y) {
      |              ^
/usr/include/c++/14/bits/stl_iterator.h:507:5: note: candidate: 'template<class _IteratorL, class _IteratorR> constexpr bool std::operator>(const reverse_iterator<_Iterator>&, const reverse_iterator<_IteratorR>&)'
  507 |     operator>(const reverse_iterator<_IteratorL>& __x,
      |     ^~~~~~~~
/usr/include/c++/14/bits/stl_iterator.h:507:5: note:   template argument deduction/substitution failed:
a.cc:15:14: note:   'std::istream' {aka 'std::basic_istream<char>'} is not derived from 'const std::reverse_iterator<_Iterator>'
   15 |   while (cin>x && cin>y) {
      |              ^
/usr/include/c++/14/bits/stl_iterator.h:1714:5: note: candidate: 'template<class _IteratorL, class _IteratorR> constexpr bool std::operator>(const move_iterator<_IteratorL>&, const move_iterator<_IteratorR>&)'
 1714 |     operator>(const move_iterator<_IteratorL>& __x,
      |     ^~~~~~~~
/usr/include/c++/14/bits/stl_iterator.h:1714:5: note:   template argument deduction/substitution failed:
a.cc:15:14: note:   'std::istream' {aka 'std::basic_istream<char>'} is not derived from 'const std::move_iterator<_IteratorL>'
   15 |   while (cin>x && cin>y) {
      |              ^
/usr/include/c++/14/bits/stl_iterator.h:1774:5: note: candidate: 'template<class _Iterator> constexpr bool std::operator>(const move_iterator<_IteratorL>&, const move_iterator<_IteratorL>&)'
 1774 |     operator>(const move_iterator<_Iterator>& __x,
      |     ^~~~~~~~
/usr/include/c++/14/bits/stl_iterator.h:1774:5: note:   template argument deduction/substitution failed:
a.cc:15:14: note:   'std::istream' {aka 'std::basic_istream<char>'} is not derived from 'const std::move_iterator<_IteratorL>'
   15 |   while (cin>x && cin>y) {
      |              ^
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/istream:40,
                 from /usr/include/c++/14/sstream:40,
                 from /usr/include/c++/14/complex:45:
/usr/include/c++/14/string_view:695:5: note: candidate: 'template<class _CharT, class _Traits> constexpr bool std::operator>(basic_string_view<_CharT, _Traits>, basic_string_view<_CharT, _Traits>)'
  695 |     operator> (basic_string_view<_CharT, _Traits> __x,
      |     ^~~~~~~~
/usr/include/c++/14/string_view:695:5: note:   template argument deduction/substitution failed:
a.cc:15:14: note:   'std::basic_istream<char>' is not derived from 'std::basic_string_view<_CharT, _Traits>'
   15 |   while (cin>x && cin>y) {
      |              ^
/usr/include/c++/14/string_view:702:5: note: candidate: 'template<class _CharT, class _Traits> constexpr bool std::operator>(basic_string_view<_CharT, _Traits>, __type_identity_t<basic_string_view<_CharT, _Traits> >)'
  702 |     operator> (basic_string_view<_CharT, _Traits> __x,
      |     ^~~~~~~~
/usr/include/c++/14/string_view:702:5: note:   template argument deduction/substitution failed:
a.cc:15:14: note:   'std::basic_istream<char>' is not derived from 'std::basic_string_view<_CharT, _Traits>'
   15 |   while (cin>x && cin>y) {
      |              ^
/usr/include/c++/14/string_view:710:5: note: candidate: 'template<class _CharT, class _Traits> constexpr bool std::operator>(__type_identity_t<basic_string_view<_CharT, _Traits> >, basic_string_view<_CharT, _Traits>)'
  710 |     operator> (__type_identity_t<basic_string_view<_CharT, _Traits>> __x,
      |     ^~~~~~~~
/usr/include/c++/14/string_view:710:5: note:   template argument deduction/substitution failed:
a.cc:15:14: note:   mismatched types 'std::basic_string_view<_CharT, _Traits>' and 'double'
   15 |   while (cin>x && cin>y) {
      |              ^
/usr/include/c++/14/bits/basic_string.h:3915:5: 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>&)'
 3915 |     operator>(const basic_string<_CharT, _Traits, _Alloc>& __lhs,
      |     ^~~~~~~~
/usr/include/c++/14/bits/basic_string.h:3915:5: note:   template argument deduction/substitution failed:
a.cc:15:14: note:   'std::istream' {aka 'std::basic_istream<char>'} is not derived from 'const std::__cxx11::basic_string<_CharT, _Traits, _Allocator>'
   15 |   while (cin>x && cin>y) {
      |              ^
/usr/include/c++/14/bits/basic_string.h:3929:5: note: candidate: 'template<class _CharT, class _Traits, class _Alloc> bool std::operator>(const __cxx11::basic_string<_CharT, _Traits, _Allocator>&, const _CharT*)'
 3929 |     operator>(const basic_string<_CharT, _Traits, _Alloc>& __lhs,
      |     ^~~~~~~~
/usr/include/c++/14/bits/basic_string.h:3929:5: note:   template argument deduction/substitution failed:
a.cc:15:14: note:   'std::istream' {aka 'std::basic_istream<char>'} is not derived from 'const std::__cxx11::basic_string<_CharT, _Traits, _Allocator>'
   15 |   while (cin>x && cin>y) {
      |              ^
/usr/include/c++/14/bits/basic_string.h:3942:5: note: candidate: 'template<class _CharT, class _Traits, class _Alloc> bool std::operator>(const _CharT*, const __cxx11::basic_string<_CharT, _Traits, _Allocator>&)'
 3942 |     operator>(const _CharT* __lhs,
      |     ^~~~~~~~
/usr/include/c++/14/bits/basic_string.h:3942:5: note:   template argument deduction/substitution failed:
a.cc:15:14: note:   mismatched types 'const _CharT*' and 'std::basic_istream<char>'
   15 |   while (cin>x && cin>y) {
      |              ^
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:2619:5: note: candidate: 'template<class ... _TElements, class ... _UElements> constexpr bool std::operator>(const tuple<_UTypes ...>&, const tuple<_Elements ...>&)'
 2619 |     operator>(const tuple<_TElements...>& __t,
      |     ^~~~~~~~
/usr/include/c++/14/tuple:2619:5: note:   template argument deduction/substitution failed:
a.cc:15:14: note:   'std::istream' {aka 'std::basic_istream<char>'} is not derived from 'const std::tuple<_UTypes ...>'
   15 |   while (cin>x && cin>y) {
      |              ^
a.cc:15:22: error: no match for 'operator>' (operand types are 'std::istream' {aka 'std::basic_istream<char>'} and 'double')
   15 |   while (cin>x && cin>y) {
      |                   ~~~^~
      |                   |   |
      |                   |   double
      |                   std::istream {aka std::basic_istream<char>}
a.cc:15:22: note: candidate: 'operator>(int, double)' (built-in)
   15 |   while (cin>x && cin>y) {
      |                   ~~~^~
a.cc:15:22: note:   no known conversion for argument 1 from 'std::istream' {aka 'std::basic_istream<char>'} to 'int'
/usr/include/c++/14/bits/stl_pair.h:1058:5: note: candidate: 'template<class _T1, class _T2> constexpr bool std::operator>(const pair<_T1, _T2>&, const pair<_T1, _T2>&)'
 1058 |     operator>(const pair<_T1, _T2>& __x, const pair<_T1, _T2>& __y)
      |     ^~~~~~~~
/usr/include/c++/14/bits/stl_pair.h:1058:5: note:   template argument deduction/substitution failed:
a.cc:15:23: note:   'std::istream' {aka 'std::basic_istream<char>'} is not derived from 'const std::pair<_T1, _T2>'
   15 |   while (cin>x && cin>y) {
      |                       ^
/usr/include/c++/14/bits/stl_iterator.h:462:5: note: candidate: 'template<class _Iterator> constexpr bool std::operator>(const reverse_iterator<_Iterator>&, const reverse_iterator<_Iterator>&)'
  462 |     operator>(const reverse_iterator<_Iterator>& __x,
      |     ^~~~~~~~
/usr/include/c++/14/bits/stl_iterator.h:462:5: note:   template argument deduction/substitution failed:
a.cc:15:23: note:   'std::istream' {aka 'std::basic_istream<char>'} is not derived from 'const std::reverse_iterator<_Iterator>'
   15 |   while (cin>x && cin>y) {
      |                       ^
/usr/include/c++/14/bits/stl_iterator.h:507:5: note: candidate: 'template<class _IteratorL, class _IteratorR> constexpr bool std::operator>(const reverse_iterator<_Iterator>&, const r