Language: C++

//AUTHOR:- Avinash//
#include <bits/stdc++.h>
#include <iostream>
using namespace std;
#define ll long long int
#define lll long long
#define fo(i,n) for(int i=0;i<n;i++)
#define take(a,i,n) for(int i=0;i<n;i++) cin>>a[i]
#define FAST ios_base::sync_with_stdio(false);cin.tie(NULL);
#define ld long long double
#define d1(x) cout<<(x)<<endl
#define T int t;cin>>t;while(t--)
#define hell 1000000007
#define ex endl;
#define F first
#define maxn 200001
#define pi 3.14159265
#define S second
#define P pair<int,int>
#define PP pair<int,pair<int,int>>
#define pb push_back
#define in insert
#define vec vector<ll>
#define vec2 vector<vector<int>>
#define s(a,n) sort(a,a+n);
#define sv(a) sort(a.begin(),a.end());
#define MAX 1000
//Author:-Avinash//

ll power(ll x, ll y, ll m)
{
    if (y == 0)
        return 1;
    ll p = power(x, y/2, m) % m;
    p = (p * p) % m;
    return (y%2 == 0)? p : (x * p) % m;
}
ll sum_of_natural_no(ll n )
{
    return (n *(n+1))/2;
}

ll modInverse(ll a, ll m)
{
    return power(a, m-2, m);
}
int main(){
   FAST
   ll a,b,c,d;
   cin>>a>>b>>c>>d;
   int ans = -1e18;
   ans = max({ans,a*c,a*d,b*c,b*d});
   cout<<ans<<endl;
   return 0;
}

Compiler output:
a.cc: In function 'int main()':
a.cc:51:14: warning: overflow in conversion from 'double' to 'int' changes value from '-1.0e+18' to '-2147483648' [-Woverflow]
   51 |    int ans = -1e18;
      |              ^~~~~
a.cc:52:13: error: no matching function for call to 'max(<brace-enclosed initializer list>)'
   52 |    ans = max({ans,a*c,a*d,b*c,b*d});
      |          ~~~^~~~~~~~~~~~~~~~~~~~~~~
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:2:
/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:52:13: note:   deduced conflicting types for parameter '_Tp' ('int' and 'long long int')
   52 |    ans = max({ans,a*c,a*d,b*c,b*d});
      |          ~~~^~~~~~~~~~~~~~~~~~~~~~~
/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