Language: C++

// SeeAlso: https://atcoder.jp/contests/abc144/tasks/abc145_c

#include <bits/stdc++.h>

using namespace std;

typedef long long ll;
typedef vector<int> vi;
typedef vector<ll> vl;
typedef pair<int,int> pii;
typedef pair<ll,ll> pll;

#define MAX 100000
#define NIL -1
#define MOD 1000000007

typedef int _loop_int;
#define rep(i,n) for(int i = 0; i < n; i++)
#define FOR(i,a,b) for(_loop_int i=(_loop_int)(a);i<(_loop_int)(b);++i)
#define FORR(i,a,b) for(_loop_int i=(_loop_int)(b)-1;i>=(_loop_int)(a);--i)

#define debug(x) cout<<#x<<": "<<x<<endl
#define debig_vec(v) cout<<#v<<":";rep(i,v.size())cout<<" "<<v[i];cout<<endl
#define ALL(a) (a).begin(),(a).end()

// 最大公約数
inline constexpr ll gcd(ll a,ll b){if(!a||!b)return 0;while(b){ll c=b;b=a%b;a=c;}return a;}
// 最小公倍数
inline constexpr ll lcm(ll a,ll b){if(!a||!b)return 0;return a*b/gcd(a,b);}

#define print2D(h, w, arr) rep(i, h) { rep(j, w) cout << arr[i][j] << " "; cout << endl; }
template<class T> void print(const T& x){cout << setprecision(12) << x << endl;}
template<class T, class... A> void print(const T& first, const A&... rest) { cout << first << " "; print(rest...); }

double sum = 0;
int n;
int x[8], y[8];

void length() {
    rep(i, n) {
        for(int j=i+1, j<n;j++) {
            double hogex = pow((x[i]-x[j]), 2);
            double hogey = pow((y[i]-y[j]), 2);
            sum += pow(hogex, hogey, 1/2);
        }
    }
    return;
}

int rec(int s) {
    if(s>0) {
        return s * rec(s-1);
    }
    return s;
}

int main() {
    int n;
    cin >> n;

    rep(i, n) {
        cin >> x[i] >> y[i];
    }

    length();

    int pattern = rec(n);
    
    double ans = (pattern-1) * sum / pattern;
    print(ans);
    return 0;
}


Compiler output:
a.cc: In function 'void length()':
a.cc:41:25: error: expected ';' before '<' token
   41 |         for(int j=i+1, j<n;j++) {
      |                         ^
      |                         ;
a.cc:41:25: error: expected primary-expression before '<' token
a.cc:44:23: error: no matching function for call to 'pow(double&, double&, int)'
   44 |             sum += pow(hogex, hogey, 1/2);
      |                    ~~~^~~~~~~~~~~~~~~~~~~
In file included from /usr/include/c++/14/valarray:605,
                 from /usr/include/x86_64-linux-gnu/c++/14/bits/stdc++.h:166,
                 from a.cc:3:
/usr/include/c++/14/bits/valarray_after.h:549:1: note: candidate: 'template<class _Tp> std::_Expr<std::__detail::_BinClos<std::_Pow, std::_Constant, std::_ValArray, _Tp, _Tp>, _Tp> std::pow(const typename valarray<_Tp>::value_type&, const valarray<_Tp>&)'
  549 | _DEFINE_EXPR_BINARY_FUNCTION(pow, struct std::_Pow)
      | ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
/usr/include/c++/14/bits/valarray_after.h:549:1: note:   candidate expects 2 arguments, 3 provided
/usr/include/c++/14/bits/valarray_after.h:549:1: note: candidate: 'template<class _Tp> std::_Expr<std::__detail::_BinClos<std::_Pow, std::_ValArray, std::_Constant, _Tp, _Tp>, _Tp> std::pow(const valarray<_Tp>&, const typename valarray<_Tp>::value_type&)'
  549 | _DEFINE_EXPR_BINARY_FUNCTION(pow, struct std::_Pow)
      | ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
/usr/include/c++/14/bits/valarray_after.h:549:1: note:   candidate expects 2 arguments, 3 provided
/usr/include/c++/14/bits/valarray_after.h:549:1: note: candidate: 'template<class _Tp> std::_Expr<std::__detail::_BinClos<std::_Pow, std::_ValArray, std::_ValArray, _Tp, _Tp>, _Tp> std::pow(const valarray<_Tp>&, const valarray<_Tp>&)'
  549 | _DEFINE_EXPR_BINARY_FUNCTION(pow, struct std::_Pow)
      | ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
/usr/include/c++/14/bits/valarray_after.h:549:1: note:   candidate expects 2 arguments, 3 provided
/usr/include/c++/14/bits/valarray_after.h:549:1: note: candidate: 'template<class _Dom> std::_Expr<std::__detail::_BinClos<std::_Pow, std::_Constant, std::_Expr, typename _Dom::value_type, _Dom>, typename _Dom::value_type> std::pow(const typename _Dom::value_type&, const _Expr<_Dom1, typename _Dom1::value_type>&)'
  549 | _DEFINE_EXPR_BINARY_FUNCTION(pow, struct std::_Pow)
      | ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
/usr/include/c++/14/bits/valarray_after.h:549:1: note:   candidate expects 2 arguments, 3 provided
/usr/include/c++/14/bits/valarray_after.h:549:1: note: candidate: 'template<class _Dom> std::_Expr<std::__detail::_BinClos<std::_Pow, std::_Expr, std::_Constant, _Dom, typename _Dom::value_type>, typename _Dom::value_type> std::pow(const _Expr<_Dom1, typename _Dom1::value_type>&, const typename _Dom::value_type&)'
  549 | _DEFINE_EXPR_BINARY_FUNCTION(pow, struct std::_Pow)
      | ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
/usr/include/c++/14/bits/valarray_after.h:549:1: note:   candidate expects 2 arguments, 3 provided
/usr/include/c++/14/bits/valarray_after.h:549:1: note: candidate: 'template<class _Dom> std::_Expr<std::__detail::_BinClos<std::_Pow, std::_ValArray, std::_Expr, typename _Dom::value_type, _Dom>, typename _Dom::value_type> std::pow(const valarray<typename _Dom::valarray>&, const _Expr<_Dom1, typename _Dom1::value_type>&)'
  549 | _DEFINE_EXPR_BINARY_FUNCTION(pow, struct std::_Pow)
      | ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
/usr/include/c++/14/bits/valarray_after.h:549:1: note:   candidate expects 2 arguments, 3 provided
/usr/include/c++/14/bits/valarray_after.h:549:1: note: candidate: 'template<class _Dom> std::_Expr<std::__detail::_BinClos<std::_Pow, std::_Expr, std::_ValArray, _Dom, typename _Dom::value_type>, typename _Dom::value_type> std::pow(const _Expr<_Dom1, typename _Dom1::value_type>&, const valarray<typename _Dom::value_type>&)'
  549 | _DEFINE_EXPR_BINARY_FUNCTION(pow, struct std::_Pow)
      | ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
/usr/include/c++/14/bits/valarray_after.h:549:1: note:   candidate expects 2 arguments, 3 provided
/usr/include/c++/14/bits/valarray_after.h:549:1: note: candidate: 'template<class _Dom1, class _Dom2> std::_Expr<std::__detail::_BinClos<std::_Pow, std::_Expr, std::_Expr, _Dom1, _Dom2>, typename _Dom1::value_type> std::pow(const _Expr<_Dom1, typename _Dom1::value_type>&, const _Expr<_Dom2, typename _Dom2::value_type>&)'
  549 | _DEFINE_EXPR_BINARY_FUNCTION(pow, struct std::_Pow)
      | ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
/usr/include/c++/14/bits/valarray_after.h:549:1: note:   candidate expects 2 arguments, 3 provided
In file included from /usr/include/c++/14/ccomplex:39,
                 from /usr/include/x86_64-linux-gnu/c++/14/bits/stdc++.h:127:
/usr/include/c++/14/complex:2482:5: note: candidate: 'template<class _Tp, class _Up> std::complex<typename __gnu_cxx::__promote<decltype (((typename __gnu_cxx::__promote<_Tp, std::__is_integer<_Tp>::__value>::__type)(0) + (typename __gnu_cxx::__promote<_Up, std::__is_integer<_Up>::__value>::__type)(0)))>::__type> std::pow(const complex<_Tp>&, const complex<_Up>&)'
 2482 |     pow(const std::complex<_Tp>& __x, const std::complex<_Up>& __y)
      |     ^~~
/usr/include/c++/14/complex:2482:5: note:   candidate expects 2 arguments, 3 provided
/usr/include/c++/14/complex:2474:5: note: candidate: 'template<class _Tp, class _Up> std::complex<typename __gnu_cxx::__promote<decltype (((typename __gnu_cxx::__promote<_Tp, std::__is_integer<_Tp>::__value>::__type)(0) + (typename __gnu_cxx::__promote<_Up, std::__is_integer<_Up>::__value>::__type)(0)))>::__type> std::pow(const _Tp&, const complex<_Up>&)'
 2474 |     pow(const _Tp& __x, const std::complex<_Up>& __y)
      |     ^~~
/usr/include/c++/14/complex:2474:5: note:   candidate expects 2 arguments, 3 provided
/usr/include/c++/14/complex:2466:5: note: candidate: 'template<class _Tp, class _Up> std::complex<typename __gnu_cxx::__promote<decltype (((typename __gnu_cxx::__promote<_Tp, std::__is_integer<_Tp>::__value>::__type)(0) + (typename __gnu_cxx::__promote<_Up, std::__is_integer<_Up>::__value>::__type)(0)))>::__type> std::pow(const complex<_Tp>&, const _Up&)'
 2466 |     pow(const std::complex<_Tp>& __x, const _Up& __y)
      |     ^~~
/usr/include/c++/14/complex:2466:5: note:   candidate expects 2 arguments, 3 provided
/usr/include/c++/14/complex:1339:5: note: candidate: 'template<class _Tp> std::complex<_Tp> std::pow(const _Tp&, const complex<_Tp>&)'
 1339 |     pow(const _Tp& __x, const complex<_Tp>& __y)
      |     ^~~
/usr/include/c++/14/complex:1339:5: note:   candidate expects 2 arguments, 3 provided
/usr/include/c++/14/complex:1328:5: note: candidate: 'template<class _Tp> std::complex<_Tp> std::pow(const complex<_Tp>&, const complex<_Tp>&)'
 1328 |     pow(const complex<_Tp>& __x, const complex<_Tp>& __y)
      |     ^~~
/usr/include/c++/14/complex:1328:5: note:   candidate expects 2 arguments, 3 provided
/usr/include/c++/14/complex:1294:5: note: candidate: 'template<class _Tp> std::complex<_Tp> std::pow(const complex<_Tp>&, const _Tp&)'
 1294 |     pow(const complex<_Tp>& __x, const _Tp& __y)
      |     ^~~
/usr/include/c++/14/complex:1294:5: note:   candidate expects 2 arguments, 3 provided
/usr/include/c++/14/complex:1285:5: note: candidate: 'template<class _Tp> std::complex<_Tp> std::pow(const complex<_Tp>&, int)'
 1285 |     pow(const complex<_Tp>& __z, int __n)
      |     ^~~
/usr/include/c++/14/complex:1285:5: note:   candidate expects 2 arguments, 3 provided
In file included from /usr/include/x86_64-linux-gnu/c++/14/bits/stdc++.h:114:
/usr/include/c++/14/cmath:1074:5: note: candidate: 'template<class _Tp, class _Up> constexpr typename __gnu_cxx::__promote_2<_Tp, _Up>::__type std::pow(_Tp, _Up)'
 1074 |     pow(_Tp __x, _Up __y)
      |     ^~~
/usr/include/c++/14/cmath:1074:5: note:   candidate expects 2 arguments, 3 provided
In file included from /usr/include/features.h:523,
                 from /usr/include/x86_64-linux-gnu/c++/14/bits/os_defines.h:39,
                 from /usr/include/x86_64-linux-gnu/c++/14/bits/c++config.h:683,
                 from /usr/include/c++/14/cassert:43,
                 from /usr/include/x86_64-linux-gnu/c++/14/bits/stdc++.h:33:
/usr/include/x86_64-linux-gnu/bits/mathcalls.h:173:1: note: candidate: 'double pow(double, double)'
  173 | __MATHCALL_VEC (pow,, (_Mdouble_ __x, _Mdouble_ __y));
      | ^~~~~~~~~~~~~~
/usr/include/x86_64-linux-gnu/bits/mathcalls.h:173:1: note:   candidate expects 2 arguments, 3 provided
/usr/include/c++/14/cmath:380:3: note: candidate: 'constexpr long double std::pow(long double, long double)'
  380 |   pow(long double __x, long double __y)
      |   ^~~
/usr/include/c++/14/cmath:380:3: note:   candidate expects 2 arguments, 3 provided
/usr/include/c++/14/cmath:376:3: note: candidate: 'constexpr float std::pow(float, float)'
  376 |   pow(float __x, float __y)
      |   ^~~
/usr/include/c++/14/cmath:376:3: note:   candidate expects 2 arguments, 3 provided