Language: C++

#include<bits/stdc++.h>
using namespace std;
int main() {
	int N;
	cin >> N;
	vector<int> x(N);
	vector<int> y(N);
	for (int i = 0; i < N; i++) {
		cin >> x[i] >> y[j];
	}
	/*ある辺が何度使われるか：X
	分子＝sum{(辺の長さ)*X}*/
	auto dist = [&](int i, int j) {
		double dx = x[i] - x[j];
		double dy = x[i] - x[j];
		return sqrt(dx * dx + dy * dy);
	};
	double len = 0;
	for (int i = 0; i < N; i++) {
		for (int j = 0; j < i; j++) {
			len += dist(i, j);
		}
	}
		int x = 2; /*分子*/
		for (int i = N - 1; i >= 1; i--) {
			x *= i;
		}
		int fact = 1; /*分母*/
		for (int i = N; i >= 1; i--) {
			fact *= i;
		}
		double ans = (len * x) / fact;
		printf("%.10f\n", ans);
	
	return 0;
}

Compiler output:
a.cc: In function 'int main()':
a.cc:9:34: error: 'j' was not declared in this scope
    9 |                 cin >> x[i] >> y[j];
      |                                  ^
a.cc:24:21: error: conflicting declaration 'int x'
   24 |                 int x = 2; /*分子*/
      |                     ^
a.cc:6:21: note: previous declaration as 'std::vector<int> x'
    6 |         vector<int> x(N);
      |                     ^
a.cc:26:27: error: no match for 'operator*=' (operand types are 'std::vector<int>' and 'int')
   26 |                         x *= i;
      |                         ~~^~~~
a.cc:32:35: error: no match for 'operator*' (operand types are 'double' and 'std::vector<int>')
   32 |                 double ans = (len * x) / fact;
      |                               ~~~ ^ ~
      |                               |     |
      |                               |     std::vector<int>
      |                               double
In file included 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/complex:400:5: note: candidate: 'template<class _Tp> std::complex<_Tp> std::operator*(const complex<_Tp>&, const complex<_Tp>&)'
  400 |     operator*(const complex<_Tp>& __x, const complex<_Tp>& __y)
      |     ^~~~~~~~
/usr/include/c++/14/complex:400:5: note:   template argument deduction/substitution failed:
a.cc:32:37: note:   mismatched types 'const std::complex<_Tp>' and 'double'
   32 |                 double ans = (len * x) / fact;
      |                                     ^
/usr/include/c++/14/complex:409:5: note: candidate: 'template<class _Tp> std::complex<_Tp> std::operator*(const complex<_Tp>&, const _Tp&)'
  409 |     operator*(const complex<_Tp>& __x, const _Tp& __y)
      |     ^~~~~~~~
/usr/include/c++/14/complex:409:5: note:   template argument deduction/substitution failed:
a.cc:32:37: note:   mismatched types 'const std::complex<_Tp>' and 'double'
   32 |                 double ans = (len * x) / fact;
      |                                     ^
/usr/include/c++/14/complex:418:5: note: candidate: 'template<class _Tp> std::complex<_Tp> std::operator*(const _Tp&, const complex<_Tp>&)'
  418 |     operator*(const _Tp& __x, const complex<_Tp>& __y)
      |     ^~~~~~~~
/usr/include/c++/14/complex:418:5: note:   template argument deduction/substitution failed:
a.cc:32:37: note:   'std::vector<int>' is not derived from 'const std::complex<_Tp>'
   32 |                 double ans = (len * x) / fact;
      |                                     ^
In file included from /usr/include/c++/14/valarray:605,
                 from /usr/include/x86_64-linux-gnu/c++/14/bits/stdc++.h:166:
/usr/include/c++/14/bits/valarray_after.h:407:5: note: candidate: 'template<class _Dom1, class _Dom2> std::_Expr<std::__detail::_BinClos<std::__multiplies, std::_Expr, std::_Expr, _Dom1, _Dom2>, typename std::__fun<std::__multiplies, typename _Dom1::value_type>::result_type> std::operator*(const _Expr<_Dom1, typename _Dom1::value_type>&, const _Expr<_Dom2, typename _Dom2::value_type>&)'
  407 |     _DEFINE_EXPR_BINARY_OPERATOR(*, struct std::__multiplies)
      |     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
/usr/include/c++/14/bits/valarray_after.h:407:5: note:   template argument deduction/substitution failed:
a.cc:32:37: note:   mismatched types 'const std::_Expr<_Dom1, typename _Dom1::value_type>' and 'double'
   32 |                 double ans = (len * x) / fact;
      |                                     ^
/usr/include/c++/14/bits/valarray_after.h:407:5: note: candidate: 'template<class _Dom> std::_Expr<std::__detail::_BinClos<std::__multiplies, std::_Expr, std::_Constant, _Dom, typename _Dom::value_type>, typename std::__fun<std::__multiplies, typename _Dom1::value_type>::result_type> std::operator*(const _Expr<_Dom1, typename _Dom1::value_type>&, const typename _Dom::value_type&)'
  407 |     _DEFINE_EXPR_BINARY_OPERATOR(*, struct std::__multiplies)
      |     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
/usr/include/c++/14/bits/valarray_after.h:407:5: note:   template argument deduction/substitution failed:
a.cc:32:37: note:   mismatched types 'const std::_Expr<_Dom1, typename _Dom1::value_type>' and 'double'
   32 |                 double ans = (len * x) / fact;
      |                                     ^
/usr/include/c++/14/bits/valarray_after.h:407:5: note: candidate: 'template<class _Dom> std::_Expr<std::__detail::_BinClos<std::__multiplies, std::_Constant, std::_Expr, typename _Dom::value_type, _Dom>, typename std::__fun<std::__multiplies, typename _Dom1::value_type>::result_type> std::operator*(const typename _Dom::value_type&, const _Expr<_Dom1, typename _Dom1::value_type>&)'
  407 |     _DEFINE_EXPR_BINARY_OPERATOR(*, struct std::__multiplies)
      |     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
/usr/include/c++/14/bits/valarray_after.h:407:5: note:   template argument deduction/substitution failed:
a.cc:32:37: note:   'std::vector<int>' is not derived from 'const std::_Expr<_Dom1, typename _Dom1::value_type>'
   32 |                 double ans = (len * x) / fact;
      |                                     ^
/usr/include/c++/14/bits/valarray_after.h:407:5: note: candidate: 'template<class _Dom> std::_Expr<std::__detail::_BinClos<std::__multiplies, std::_Expr, std::_ValArray, _Dom, typename _Dom::value_type>, typename std::__fun<std::__multiplies, typename _Dom1::value_type>::result_type> std::operator*(const _Expr<_Dom1, typename _Dom1::value_type>&, const valarray<typename _Dom::value_type>&)'
  407 |     _DEFINE_EXPR_BINARY_OPERATOR(*, struct std::__multiplies)
      |     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
/usr/include/c++/14/bits/valarray_after.h:407:5: note:   template argument deduction/substitution failed:
a.cc:32:37: note:   mismatched types 'const std::_Expr<_Dom1, typename _Dom1::value_type>' and 'double'
   32 |                 double ans = (len * x) / fact;
      |                                     ^
/usr/include/c++/14/bits/valarray_after.h:407:5: note: candidate: 'template<class _Dom> std::_Expr<std::__detail::_BinClos<std::__multiplies, std::_ValArray, std::_Expr, typename _Dom::value_type, _Dom>, typename std::__fun<std::__multiplies, typename _Dom1::value_type>::result_type> std::operator*(const valarray<typename _Dom::value_type>&, const _Expr<_Dom1, typename _Dom1::value_type>&)'
  407 |     _DEFINE_EXPR_BINARY_OPERATOR(*, struct std::__multiplies)
      |     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
/usr/include/c++/14/bits/valarray_after.h:407:5: note:   template argument deduction/substitution failed:
a.cc:32:37: note:   'std::vector<int>' is not derived from 'const std::_Expr<_Dom1, typename _Dom1::value_type>'
   32 |                 double ans = (len * x) / fact;
      |                                     ^
/usr/include/c++/14/valarray:1198:1: note: candidate: 'template<class _Tp> std::_Expr<std::__detail::_BinClos<std::__multiplies, std::_ValArray, std::_ValArray, _Tp, _Tp>, typename std::__fun<std::__multiplies, _Tp>::result_type> std::operator*(const valarray<_Tp>&, const valarray<_Tp>&)'
 1198 | _DEFINE_BINARY_OPERATOR(*, __multiplies)
      | ^~~~~~~~~~~~~~~~~~~~~~~
/usr/include/c++/14/valarray:1198:1: note:   template argument deduction/substitution failed:
a.cc:32:37: note:   mismatched types 'const std::valarray<_Tp>' and 'double'
   32 |                 double ans = (len * x) / fact;
      |                                     ^
/usr/include/c++/14/valarray:1198:1: note: candidate: 'template<class _Tp> std::_Expr<std::__detail::_BinClos<std::__multiplies, std::_ValArray, std::_Constant, _Tp, _Tp>, typename std::__fun<std::__multiplies, _Tp>::result_type> std::operator*(const valarray<_Tp>&, const typename valarray<_Tp>::value_type&)'
 1198 | _DEFINE_BINARY_OPERATOR(*, __multiplies)
      | ^~~~~~~~~~~~~~~~~~~~~~~
/usr/include/c++/14/valarray:1198:1: note:   template argument deduction/substitution failed:
a.cc:32:37: note:   mismatched types 'const std::valarray<_Tp>' and 'double'
   32 |                 double ans = (len * x) / fact;
      |                                     ^
/usr/include/c++/14/valarray:1198:1: note: candidate: 'template<class _Tp> std::_Expr<std::__detail::_BinClos<std::__multiplies, std::_Constant, std::_ValArray, _Tp, _Tp>, typename std::__fun<std::__multiplies, _Tp>::result_type> std::operator*(const typename valarray<_Tp>::value_type&, const valarray<_Tp>&)'
 1198 | _DEFINE_BINARY_OPERATOR(*, __multiplies)
      | ^~~~~~~~~~~~~~~~~~~~~~~
/usr/include/c++/14/valarray:1198:1: note:   template argument deduction/substitution failed:
a.cc:32:37: note:   'std::vector<int>' is not derived from 'const std::valarray<_Tp>'
   32 |                 double ans = (len * x) / fact;
      |                                     ^