Language: C++

#include <iostream>
#include <string>
#include <algorithm>
#include <ctime>
#include <functional>
#include <vector>
#include <stack>
#include <queue>
#include <map>
#include <set>
#include <cassert>
#include <bitset>
#include <list>
#include <cstdio>
#include <stdio.h>
#include <string.h>
#include <limits.h>
#include <math.h>
#include <cmath>
#include <tuple>
#include <cassert>
#include <array>
#include <iomanip>

using namespace std;
using ll = long long;
using pii = pair<int, int>;
using ti = tuple<int, int, int>;

#define pb push_back
#define mp make_pair
#define debug(x) cerr << #x << ": " << x << endl
// #define int long long 

const double eps=1e-14;
const int mod = 1e9 + 7;
const int inf = ((1<<30)-1);
const ll linf = (1LL<<60);
const int dx[4] = {1, 0, -1, 0};
const int dy[4] = {0, 1, 0, -1};

int n, m, q;
vector<int> a, b, c, d;

void dfs(vector<int> A)
{
    if(A.size() == n+1)
    {
        int now = 0;
        for(int i=0; i<q; i++)
        {
            if(A[b[i]] - A[a[i]] == c[i]) now += d[i];
        }
        ans = max()
        return ;
    }
    A.push_back(A.back());
    while(A.back() <= m)
    {
        dfs(A);
        A.back()++;
    }
}

int main()
{
    cin.tie(0);
    ios::sync_with_stdio(false);
    cin >> n >> m >> q;
    a = b = c = d = vector<int>(q);
    for(int i=0; i<q; i++) cin >> a[i] >> b[i] >> c[i] >> d[i];
    dfs(vector<int>(1,1));
    cout << ans << endl;
    return 0;
}

Compiler output:
a.cc: In function 'void dfs(std::vector<int>)':
a.cc:54:9: error: 'ans' was not declared in this scope; did you mean 'abs'?
   54 |         ans = max()
      |         ^~~
      |         abs
a.cc:54:18: error: no matching function for call to 'max()'
   54 |         ans = max()
      |               ~~~^~
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:   candidate expects 2 arguments, 0 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, 0 provided
In file included from /usr/include/c++/14/algorithm:61,
                 from a.cc:3:
/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, 0 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:   candidate expects 2 arguments, 0 provided
a.cc: In function 'int main()':
a.cc:73:13: error: 'ans' was not declared in this scope; did you mean 'abs'?
   73 |     cout << ans << endl;
      |             ^~~
      |             abs