Language: C++

clude <bits/stdc++.h>
using namespace std;
/*#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
using namespace __gnu_pbds;
template<typename T> using gpp_set = tree<T, null_type, less<T>, rb_tree_tag, tree_order_statistics_node_update>;
template<typename T, typename L> using gpp_map = tree<T, L, less<T>, rb_tree_tag, tree_order_statistics_node_update>;
template<typename T> using gpp_multiset = tree<T, null_type, less_equal<T>, rb_tree_tag, tree_order_statistics_node_update>;*/
struct fast_ios { fast_ios(){ cin.tie(0); ios::sync_with_stdio(false); cout << fixed << setprecision(20); }; } fast_ios_;
#define FOR(i, begin, end) for(int i=(begin);i<(end);i++)
#define REP(i, n) FOR(i,0,n)
#define IFOR(i, begin, end) for(int i=(end)-1;i>=(begin);i--)
#define IREP(i, n) IFOR(i,0,n)
#define Sort(v) sort(v.begin(), v.end())
#define Reverse(v) reverse(v.begin(), v.end())
#define all(v) v.begin(),v.end()
#define SZ(v) ((int)v.size())
#define Lower_bound(v, x) distance(v.begin(), lower_bound(v.begin(), v.end(), x))
#define Upper_bound(v, x) distance(v.begin(), upper_bound(v.begin(), v.end(), x))
#define Max(a, b) a = max(a, b)
#define Min(a, b) a = min(a, b)
#define bit(n) (1LL<<(n))
#define bit_exist(x, n) ((x >> n) & 1)
#define debug(x) cout << #x << "=" << x << endl;
#define vdebug(v) cout << #v << "=" << endl; REP(i_debug, v.size()){ cout << v[i_debug] << ","; } cout << endl;
#define mdebug(m) cout << #m << "=" << endl; REP(i_debug, m.size()){ REP(j_debug, m[i_debug].size()){ cout << m[i_debug][j_debug] << ","; } cout << endl;}
#define pb push_back
#define f first
#define s second
#define int long long
#define INF 1000000000000000000
template<typename T> istream &operator>>(istream &is, vector<T> &v){ for (auto &x : v) is >> x; return is; }
template<typename T> ostream &operator<<(ostream &os, vector<T> &v){ for(int i = 0; i < v.size(); i++) { cout << v[i]; if(i != v.size() - 1) cout << endl; }; return os; }
template<typename T> void Out(T x) { cout << x << endl; }
template<typename T1, typename T2> void Ans(bool f, T1 y, T2 n) { if(f) Out(y); else Out(n); }
 
using vec = vector<int>;
using mat = vector<vec>;
using Pii = pair<int, int>;
using PiP = pair<int, Pii>;
using PPi = pair<Pii, int>;
using bools = vector<bool>;
using pairs = vector<Pii>;
 
//int dx[4] = {1,0,-1,0};
//int dy[4] = {0,1,0,-1};
//char d[4] = {'D','R','U','L'};
 
const int mod = 1000000007;
//const int mod = 998244353;
//#define Add(x, y) x = (x + (y)) % mod
//#define Mult(x, y) x = (x * (y)) % mod
 
 
 
signed main(){
 
    int N; cin >> N;
    vec d(N); cin >> d;
    int ans = 0;
    REP(i, N) REP(j, i) ans += d[i] * d[j];
    Out(ans);
 
    return 0;
}

Compiler output:
a.cc:1:1: error: 'clude' does not name a type
    1 | clude <bits/stdc++.h>
      | ^~~~~
a.cc: In constructor 'fast_ios::fast_ios()':
a.cc:9:31: error: 'cin' was not declared in this scope; did you mean 'Min'?
    9 | struct fast_ios { fast_ios(){ cin.tie(0); ios::sync_with_stdio(false); cout << fixed << setprecision(20); }; } fast_ios_;
      |                               ^~~
      |                               Min
a.cc:9:43: error: 'ios' has not been declared
    9 | struct fast_ios { fast_ios(){ cin.tie(0); ios::sync_with_stdio(false); cout << fixed << setprecision(20); }; } fast_ios_;
      |                                           ^~~
a.cc:9:72: error: 'cout' was not declared in this scope
    9 | struct fast_ios { fast_ios(){ cin.tie(0); ios::sync_with_stdio(false); cout << fixed << setprecision(20); }; } fast_ios_;
      |                                                                        ^~~~
a.cc:9:80: error: 'fixed' was not declared in this scope
    9 | struct fast_ios { fast_ios(){ cin.tie(0); ios::sync_with_stdio(false); cout << fixed << setprecision(20); }; } fast_ios_;
      |                                                                                ^~~~~
a.cc:9:89: error: 'setprecision' was not declared in this scope
    9 | struct fast_ios { fast_ios(){ cin.tie(0); ios::sync_with_stdio(false); cout << fixed << setprecision(20); }; } fast_ios_;
      |                                                                                         ^~~~~~~~~~~~
a.cc: At global scope:
a.cc:32:22: error: 'istream' does not name a type
   32 | template<typename T> istream &operator>>(istream &is, vector<T> &v){ for (auto &x : v) is >> x; return is; }
      |                      ^~~~~~~
a.cc:33:22: error: 'ostream' does not name a type
   33 | template<typename T> ostream &operator<<(ostream &os, vector<T> &v){ for(int i = 0; i < v.size(); i++) { cout << v[i]; if(i != v.size() - 1) cout << endl; }; return os; }
      |                      ^~~~~~~
a.cc: In function 'void Out(T)':
a.cc:34:38: error: 'cout' was not declared in this scope
   34 | template<typename T> void Out(T x) { cout << x << endl; }
      |                                      ^~~~
a.cc:34:51: error: 'endl' was not declared in this scope
   34 | template<typename T> void Out(T x) { cout << x << endl; }
      |                                                   ^~~~
a.cc: At global scope:
a.cc:37:13: error: 'vector' does not name a type
   37 | using vec = vector<int>;
      |             ^~~~~~
a.cc:38:13: error: 'vector' does not name a type
   38 | using mat = vector<vec>;
      |             ^~~~~~
a.cc:39:13: error: 'pair' does not name a type
   39 | using Pii = pair<int, int>;
      |             ^~~~
a.cc:40:13: error: 'pair' does not name a type
   40 | using PiP = pair<int, Pii>;
      |             ^~~~
a.cc:41:13: error: 'pair' does not name a type
   41 | using PPi = pair<Pii, int>;
      |             ^~~~
a.cc:42:15: error: 'vector' does not name a type
   42 | using bools = vector<bool>;
      |               ^~~~~~
a.cc:43:15: error: 'vector' does not name a type
   43 | using pairs = vector<Pii>;
      |               ^~~~~~
a.cc: In function 'int main()':
a.cc:58:12: error: 'cin' was not declared in this scope; did you mean 'Min'?
   58 |     int N; cin >> N;
      |            ^~~
      |            Min
a.cc:59:5: error: 'vec' was not declared in this scope
   59 |     vec d(N); cin >> d;
      |     ^~~
a.cc:59:22: error: 'd' was not declared in this scope
   59 |     vec d(N); cin >> d;
      |                      ^