Language: C++

#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
const unsigned int mod = 1000000007;
int main()
{
    ios_base::sync_with_stdio(false);
    cin.tie(NULL);
    cout.tie(NULL);
    int n,num,val;
    cin >> n;
    ll a[n];
    ll pref[n];
    cin >> num;
    a[0] = num;
    pref[0]= num;
    for(int i = 1; i < n; i++)
    {
        cin >> val;
        val = val % mod;
        a[i] = val;
    }
    for(int i = 0; i < n; i++)
    {
        if(i == 0)
        {
            pref[i] = a[i] % mod;
        }
        else
        {
            pref[i] = (pref[i-1] + a[i]) % mod;
        }
    }
    ll sum = 0;
    for(int i = 0; i < n; i++)
    {
        sum = sum + [a[i]*(pref[n-1] - pref[i])] % mod;
        sum = sum % mod;
    }
    cout << sum << "\n" ;
}


Compiler output:
a.cc: In function 'int main()':
a.cc:37:22: error: array of runtime bound cannot be captured by copy, only by reference
   37 |         sum = sum + [a[i]*(pref[n-1] - pref[i])] % mod;
      |                      ^
a.cc:37:23: error: expected ',' before '[' token
   37 |         sum = sum + [a[i]*(pref[n-1] - pref[i])] % mod;
      |                       ^
      |                       ,
a.cc:37:23: error: expected identifier before '[' token
a.cc: In lambda function:
a.cc:37:50: error: expected '{' before '%' token
   37 |         sum = sum + [a[i]*(pref[n-1] - pref[i])] % mod;
      |                                                  ^
a.cc: In function 'int main()':
a.cc:37:50: error: no match for 'operator%' (operand types are 'main()::<lambda()>' and 'const unsigned int')
   37 |         sum = sum + [a[i]*(pref[n-1] - pref[i])] % mod;
      |                     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ^ ~~~
      |                     |                              |
      |                     main()::<lambda()>             const unsigned int
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:1:
/usr/include/c++/14/bits/valarray_after.h:409:5: note: candidate: 'template<class _Dom1, class _Dom2> std::_Expr<std::__detail::_BinClos<std::__modulus, std::_Expr, std::_Expr, _Dom1, _Dom2>, typename std::__fun<std::__modulus, typename _Dom1::value_type>::result_type> std::operator%(const _Expr<_Dom1, typename _Dom1::value_type>&, const _Expr<_Dom2, typename _Dom2::value_type>&)'
  409 |     _DEFINE_EXPR_BINARY_OPERATOR(%, struct std::__modulus)
      |     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
/usr/include/c++/14/bits/valarray_after.h:409:5: note:   template argument deduction/substitution failed:
a.cc:37:52: note:   'main()::<lambda()>' is not derived from 'const std::_Expr<_Dom1, typename _Dom1::value_type>'
   37 |         sum = sum + [a[i]*(pref[n-1] - pref[i])] % mod;
      |                                                    ^~~
/usr/include/c++/14/bits/valarray_after.h:409:5: note: candidate: 'template<class _Dom> std::_Expr<std::__detail::_BinClos<std::__modulus, std::_Expr, std::_Constant, _Dom, typename _Dom::value_type>, typename std::__fun<std::__modulus, typename _Dom1::value_type>::result_type> std::operator%(const _Expr<_Dom1, typename _Dom1::value_type>&, const typename _Dom::value_type&)'
  409 |     _DEFINE_EXPR_BINARY_OPERATOR(%, struct std::__modulus)
      |     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
/usr/include/c++/14/bits/valarray_after.h:409:5: note:   template argument deduction/substitution failed:
a.cc:37:52: note:   'main()::<lambda()>' is not derived from 'const std::_Expr<_Dom1, typename _Dom1::value_type>'
   37 |         sum = sum + [a[i]*(pref[n-1] - pref[i])] % mod;
      |                                                    ^~~
/usr/include/c++/14/bits/valarray_after.h:409:5: note: candidate: 'template<class _Dom> std::_Expr<std::__detail::_BinClos<std::__modulus, std::_Constant, std::_Expr, typename _Dom::value_type, _Dom>, typename std::__fun<std::__modulus, typename _Dom1::value_type>::result_type> std::operator%(const typename _Dom::value_type&, const _Expr<_Dom1, typename _Dom1::value_type>&)'
  409 |     _DEFINE_EXPR_BINARY_OPERATOR(%, struct std::__modulus)
      |     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
/usr/include/c++/14/bits/valarray_after.h:409:5: note:   template argument deduction/substitution failed:
a.cc:37:52: note:   mismatched types 'const std::_Expr<_Dom1, typename _Dom1::value_type>' and 'const unsigned int'
   37 |         sum = sum + [a[i]*(pref[n-1] - pref[i])] % mod;
      |                                                    ^~~
/usr/include/c++/14/bits/valarray_after.h:409:5: note: candidate: 'template<class _Dom> std::_Expr<std::__detail::_BinClos<std::__modulus, std::_Expr, std::_ValArray, _Dom, typename _Dom::value_type>, typename std::__fun<std::__modulus, typename _Dom1::value_type>::result_type> std::operator%(const _Expr<_Dom1, typename _Dom1::value_type>&, const valarray<typename _Dom::value_type>&)'
  409 |     _DEFINE_EXPR_BINARY_OPERATOR(%, struct std::__modulus)
      |     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
/usr/include/c++/14/bits/valarray_after.h:409:5: note:   template argument deduction/substitution failed:
a.cc:37:52: note:   'main()::<lambda()>' is not derived from 'const std::_Expr<_Dom1, typename _Dom1::value_type>'
   37 |         sum = sum + [a[i]*(pref[n-1] - pref[i])] % mod;
      |                                                    ^~~
/usr/include/c++/14/bits/valarray_after.h:409:5: note: candidate: 'template<class _Dom> std::_Expr<std::__detail::_BinClos<std::__modulus, std::_ValArray, std::_Expr, typename _Dom::value_type, _Dom>, typename std::__fun<std::__modulus, typename _Dom1::value_type>::result_type> std::operator%(const valarray<typename _Dom::value_type>&, const _Expr<_Dom1, typename _Dom1::value_type>&)'
  409 |     _DEFINE_EXPR_BINARY_OPERATOR(%, struct std::__modulus)
      |     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
/usr/include/c++/14/bits/valarray_after.h:409:5: note:   template argument deduction/substitution failed:
a.cc:37:52: note:   mismatched types 'const std::_Expr<_Dom1, typename _Dom1::value_type>' and 'const unsigned int'
   37 |         sum = sum + [a[i]*(pref[n-1] - pref[i])] % mod;
      |                                                    ^~~
/usr/include/c++/14/valarray:1200:1: note: candidate: 'template<class _Tp> std::_Expr<std::__detail::_BinClos<std::__modulus, std::_ValArray, std::_ValArray, _Tp, _Tp>, typename std::__fun<std::__modulus, _Tp>::result_type> std::operator%(const valarray<_Tp>&, const valarray<_Tp>&)'
 1200 | _DEFINE_BINARY_OPERATOR(%, __modulus)
      | ^~~~~~~~~~~~~~~~~~~~~~~
/usr/include/c++/14/valarray:1200:1: note:   template argument deduction/substitution failed:
a.cc:37:52: note:   'main()::<lambda()>' is not derived from 'const std::valarray<_Tp>'
   37 |         sum = sum + [a[i]*(pref[n-1] - pref[i])] % mod;
      |                                                    ^~~
/usr/include/c++/14/valarray:1200:1: note: candidate: 'template<class _Tp> std::_Expr<std::__detail::_BinClos<std::__modulus, std::_ValArray, std::_Constant, _Tp, _Tp>, typename std::__fun<std::__modulus, _Tp>::result_type> std::operator%(const valarray<_Tp>&, const typename valarray<_Tp>::value_type&)'
 1200 | _DEFINE_BINARY_OPERATOR(%, __modulus)
      | ^~~~~~~~~~~~~~~~~~~~~~~
/usr/include/c++/14/valarray:1200:1: note:   template argument deduction/substitution failed:
a.cc:37:52: note:   'main()::<lambda()>' is not derived from 'const std::valarray<_Tp>'
   37 |         sum = sum + [a[i]*(pref[n-1] - pref[i])] % mod;
      |                                                    ^~~
/usr/include/c++/14/valarray:1200:1: note: candidate: 'template<class _Tp> std::_Expr<std::__detail::_BinClos<std::__modulus, std::_Constant, std::_ValArray, _Tp, _Tp>, typename std::__fun<std::__modulus, _Tp>::result_type> std::operator%(const typename valarray<_Tp>::value_type&, const valarray<_Tp>&)'
 1200 | _DEFINE_BINARY_OPERATOR(%, __modulus)
      | ^~~~~~~~~~~~~~~~~~~~~~~
/usr/include/c++/14/valarray:1200:1: note:   template argument deduction/substitution failed:
a.cc:37:52: note:   mismatched types 'const std::valarray<_Tp>' and 'const unsigned int'
   37 |         sum = sum + [a[i]*(pref[n-1] - pref[i])] % mod;
      |                                                    ^~~