Language: C++

#include<bits/stdc++.h>
using namespace std;
 
#define SPEED ios::sync_with_stdio(false); cin.tie(0); cout.tie(0)
#define MP make_pair
#define pb push_back
#define ff first
#define ss second
#define sz(x) x.size()
#define all(c) c.begin(),c.end()
#define int long long
#define fr(i,j,x) for(int i=j;i<x;i++)
#define rep(i,j,x) for(int i=j;i<=x;i++)
#define mem(x,val) memset(x,val,sizeof(x))
//#define endl '\n'
#define vi vector<int>
#define pii pair<int,int>
#define piii pair<int,pii>
 
const int mod=1e9+7;
const int N=2e5+10;
const int MAXN=2e6+10;
const int INF=1e18;

string to_string(string s) { return '"' + s + '"';}
string to_string(char s) { return string(1, s);}
string to_string(const char* s) { return to_string((string) s);}
string to_string(bool b) { return (b ? "true" : "false");}
template <typename A> string to_string(A);
template <typename A, typename B>string to_string(pair<A, B> p) {return "(" + to_string(p.first) + ", " + to_string(p.second) + ")";}
template <typename A> string to_string(A v) {bool f = 1; string r = "{"; for (const auto &x : v) {if (!f)r += ", "; f = 0; r += to_string(x);} return r + "}";}
void debug_out() { cerr << endl; }
template <typename Head, typename... Tail> void debug_out(Head H, Tail... T) {cerr << " " << to_string(H); debug_out(T...);}
#define pr(...) cerr << "[" << #__VA_ARGS__ << "]:", debug_out(__VA_ARGS__)

vi g[N];
int vis[N],n,m;
int size=0;
  
void dfs(int u){
    size++;
    vis[u]=1;
    for(auto v:g[u]){
        if(!vis[v]){
            dfs(v);
        }
    }
}

void solve(){
    cin>>n>>m;
    rep(i,1,m){
        int a,b;
        cin>>a>>b;
        g[a].pb(b);
        g[b].pb(a);
    }
    mem(vis,0);
    int ans=0;
    rep(i,1,n){
        if(!vis[i]){
            size=0;
            dfs(i);
        }
        ans=max(ans,size);
    }
    cout<<ans<<endl;
}


int32_t main()
{
    // #ifndef ONLINE_JUDGE
    //     freopen("inputf.in", "r", stdin);
    //     //freopen("outputf.in", "w", stdout);
    // #endif
    SPEED;
    int T=1;
    //cin>>T;
    int t1=1;
    while(true)
    {  
        //cout<<"Case #"<<t1<<": ";
        solve();
        t1++;
        if(t1>T)
            break;
    }
}

Compiler output:
a.cc: In function 'void dfs(long long int)':
a.cc:41:5: error: reference to 'size' is ambiguous
   41 |     size++;
      |     ^~~~
In file included from /usr/include/c++/14/string:53,
                 from /usr/include/c++/14/bitset:52,
                 from /usr/include/x86_64-linux-gnu/c++/14/bits/stdc++.h:52,
                 from a.cc:1:
/usr/include/c++/14/bits/range_access.h:272:5: note: candidates are: 'template<class _Tp, long unsigned int _Nm> constexpr std::size_t std::size(const _Tp (&)[_Nm])'
  272 |     size(const _Tp (&)[_Nm]) noexcept
      |     ^~~~
/usr/include/c++/14/bits/range_access.h:262:5: note:                 'template<class _Container> constexpr decltype (__cont.size()) std::size(const _Container&)'
  262 |     size(const _Container& __cont) noexcept(noexcept(__cont.size()))
      |     ^~~~
a.cc:38:5: note:                 'long long int size'
   38 | int size=0;
      |     ^~~~
a.cc: In function 'void solve()':
a.cc:62:13: error: reference to 'size' is ambiguous
   62 |             size=0;
      |             ^~~~
/usr/include/c++/14/bits/range_access.h:272:5: note: candidates are: 'template<class _Tp, long unsigned int _Nm> constexpr std::size_t std::size(const _Tp (&)[_Nm])'
  272 |     size(const _Tp (&)[_Nm]) noexcept
      |     ^~~~
/usr/include/c++/14/bits/range_access.h:262:5: note:                 'template<class _Container> constexpr decltype (__cont.size()) std::size(const _Container&)'
  262 |     size(const _Container& __cont) noexcept(noexcept(__cont.size()))
      |     ^~~~
a.cc:38:5: note:                 'long long int size'
   38 | int size=0;
      |     ^~~~
a.cc:65:21: error: reference to 'size' is ambiguous
   65 |         ans=max(ans,size);
      |                     ^~~~
/usr/include/c++/14/bits/range_access.h:272:5: note: candidates are: 'template<class _Tp, long unsigned int _Nm> constexpr std::size_t std::size(const _Tp (&)[_Nm])'
  272 |     size(const _Tp (&)[_Nm]) noexcept
      |     ^~~~
/usr/include/c++/14/bits/range_access.h:262:5: note:                 'template<class _Container> constexpr decltype (__cont.size()) std::size(const _Container&)'
  262 |     size(const _Container& __cont) noexcept(noexcept(__cont.size()))
      |     ^~~~
a.cc:38:5: note:                 'long long int size'
   38 | int size=0;
      |     ^~~~