Language: C++

#include <iostream>
#include <string>
#include <vector>
#include <algorithm>
#include <cmath>
#include <map>
#define rep(i, n) for(int i=0;i<n;i++)
typedef long long ll;
#define intv vector<int>
#define llv vector<long long>
#define intvv vector<vector<int>>
#define llvv vector<vector<long long>>
using namespace std;


int main(){
    int n;
    cin >> n;
    intv a[100000];
    rep(i, n) cin >> a(i);
    intv l[100000], r[100000];
    l[0] = a[0];
    r[n] = a[n];
    rep(i, n){
        l[i+1] = gcd(l[i], a[0]);
        r[n - i - 1] = gcd(r[n - i], a[n - i - 1]);
    }
    ll ans = 0;
    rep(i, n){
        ans = max(ans, max(l[i], r[i]));
    }
    cout << ans << endl;
}

Compiler output:
a.cc: In function 'int main()':
a.cc:20:23: error: 'a' cannot be used as a function
   20 |     rep(i, n) cin >> a(i);
      |                      ~^~~
a.cc:25:18: error: 'gcd' was not declared in this scope
   25 |         l[i+1] = gcd(l[i], a[0]);
      |                  ^~~
a.cc:30:18: error: no matching function for call to 'max(ll&, const std::vector<int>&)'
   30 |         ans = max(ans, max(l[i], r[i]));
      |               ~~~^~~~~~~~~~~~~~~~~~~~~~
In file included from /usr/include/c++/14/string:51,
                 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/ostream:40,
                 from /usr/include/c++/14/iostream:41,
                 from a.cc:1:
/usr/include/c++/14/bits/stl_algobase.h:257:5: note: candidate: 'template<class _Tp> constexpr const _Tp& std::max(const _Tp&, const _Tp&)'
  257 |     max(const _Tp& __a, const _Tp& __b)
      |     ^~~
/usr/include/c++/14/bits/stl_algobase.h:257:5: note:   template argument deduction/substitution failed:
a.cc:30:18: note:   deduced conflicting types for parameter 'const _Tp' ('long long int' and 'std::vector<int>')
   30 |         ans = max(ans, max(l[i], r[i]));
      |               ~~~^~~~~~~~~~~~~~~~~~~~~~
/usr/include/c++/14/bits/stl_algobase.h:303:5: note: candidate: 'template<class _Tp, class _Compare> constexpr const _Tp& std::max(const _Tp&, const _Tp&, _Compare)'
  303 |     max(const _Tp& __a, const _Tp& __b, _Compare __comp)
      |     ^~~
/usr/include/c++/14/bits/stl_algobase.h:303:5: note:   candidate expects 3 arguments, 2 provided
In file included from /usr/include/c++/14/algorithm:61,
                 from a.cc:4:
/usr/include/c++/14/bits/stl_algo.h:5706:5: note: candidate: 'template<class _Tp> constexpr _Tp std::max(initializer_list<_Tp>)'
 5706 |     max(initializer_list<_Tp> __l)
      |     ^~~
/usr/include/c++/14/bits/stl_algo.h:5706:5: note:   candidate expects 1 argument, 2 provided
/usr/include/c++/14/bits/stl_algo.h:5716:5: note: candidate: 'template<class _Tp, class _Compare> constexpr _Tp std::max(initializer_list<_Tp>, _Compare)'
 5716 |     max(initializer_list<_Tp> __l, _Compare __comp)
      |     ^~~
/usr/include/c++/14/bits/stl_algo.h:5716:5: note:   template argument deduction/substitution failed:
a.cc:30:18: note:   mismatched types 'std::initializer_list<_Tp>' and 'long long int'
   30 |         ans = max(ans, max(l[i], r[i]));
      |               ~~~^~~~~~~~~~~~~~~~~~~~~~