Language: C++

#include <bits/stdc++.h>
using namespace std;
#define ll long long int
#define pb push_back
#define mp make_pair
#define INF 0x3f3f3f3f 
#define fast_cin() ios_base::sync_with_stdio(false); cin.tie(NULL)
#define ll long long int
#define pi 3.14159265358979
#define all(x) x.begin(), x.end()
#define clr(x) memset(x, 0, sizeof(x))
#define sortall(x) sort(all(x))
#define PI 3.1415926535897932384626
#define minn INT_MAX
#define maxx INT_MIN
#define fori(i, n) for (i = 0; i < n; i++)
typedef pair<int, int>  pii;
typedef vector<int>   vi;
typedef vector<pii>   vpii;
typedef vector<vi>    vvi;
int main() {
  #ifndef ONLINE_JUDGE
    freopen("input.txt", "r", stdin);
    freopen("output.txt", "w", stdout);
  #endif
  int a,b,c,d;
  ll ans=max(a*c,max(a*d,max(b*d),max(b*c)));
  cout<<ans;
  return 0;
}

Compiler output:
a.cc: In function 'int main()':
a.cc:27:29: error: no matching function for call to 'max(int)'
   27 |   ll ans=max(a*c,max(a*d,max(b*d),max(b*c)));
      |                          ~~~^~~~~
In file included from /usr/include/c++/14/algorithm:60,
                 from /usr/include/x86_64-linux-gnu/c++/14/bits/stdc++.h:51,
                 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:   candidate expects 2 arguments, 1 provided
/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, 1 provided
In file included from /usr/include/c++/14/algorithm:61:
/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:   template argument deduction/substitution failed:
a.cc:27:29: note:   mismatched types 'std::initializer_list<_Tp>' and 'int'
   27 |   ll ans=max(a*c,max(a*d,max(b*d),max(b*c)));
      |                          ~~~^~~~~
/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:   candidate expects 2 arguments, 1 provided
a.cc:27:38: error: no matching function for call to 'max(int)'
   27 |   ll ans=max(a*c,max(a*d,max(b*d),max(b*c)));
      |                                   ~~~^~~~~
/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:   candidate expects 2 arguments, 1 provided
/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, 1 provided
/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:   template argument deduction/substitution failed:
a.cc:27:38: note:   mismatched types 'std::initializer_list<_Tp>' and 'int'
   27 |   ll ans=max(a*c,max(a*d,max(b*d),max(b*c)));
      |                                   ~~~^~~~~
/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:   candidate expects 2 arguments, 1 provided