Language: C++

#include <bits/stdc++.h>
#define fi first
#define se second
#define rep(i,n) for(int i = 0; i < (n); ++i)
#define rep2(j,n) for(int j = 0; j < (n); ++j)
#define rrep(i,n) for(int i = 1; i <= (n); ++i)
#define drep(i,n) for(int i = (n)-1; i >= 0; --i)
#define srep(i,s,t) for (int i = s; i < t; ++i)
#define srep2(j,s,t) for (int j = s; j < t; ++j)
#define rng(a) a.begin(),a.end()
#define maxs(x,y) (x = max(x,y))
#define mins(x,y) (x = min(x,y))
#define limit(x,l,r) max(l,min(x,r))
#define lims(x,l,r) (x = max(l,min(x,r)))
#define isin(x,l,r) ((l) <= (x) && (x) < (r))
#define pb push_back
#define sz(x) (int)(x).size()
#define pcnt __builtin_popcountll
#define uni(x) x.erase(unique(rng(x)),x.end())
#define snuke srand((unsigned)clock()+(unsigned)time(NULL));
#define show(x) cout<<#x<<" = "<<x<<endl;
#define PQ(T) priority_queue<T,v(T),greater<T> >
#define bn(x) ((1<<x)-1)
#define dup(x,y) (((x)+(y)-1)/(y))
#define newline puts("")
#define v(T) vector<T>
#define vv(T) v(v(T))
using namespace std;
typedef long long int ll;
typedef unsigned uint;
typedef unsigned long long ull;
typedef pair<int,int> P;
typedef set<int> S;
typedef queue<int> Q;
typedef queue<P> QP;
typedef vector<int> vi;
typedef vector<vi> vvi;
typedef vector<ll> vl;
typedef vector<P> vp;
inline int in() { int x; scanf("%d",&x); return x;}
template<typename T>inline istream& operator>>(istream&i,v(T)&v)
{rep(j,sz(v))i>>v[j];return i;}
template<typename T>string join(const v(T)&v)
{stringstream s;rep(i,sz(v))s<<' '<<v[i];return s.str().substr(1);}
template<typename T>inline ostream& operator<<(ostream&o,const v(T)&v)
{if(sz(v))o<<join(v);return o;}
template<typename T1,typename T2>inline istream& operator>>(istream&i,pair<T1,T2>&v)
{return i>>v.fi>>v.se;}
template<typename T1,typename T2>inline ostream& operator<<(ostream&o,const pair<T1,T2>&v)
{return o<<v.fi<<","<<v.se;}
template<typename T>inline ll suma(const v(T)& a) { ll res(0); for (auto&& x : a) res += x; return res;}
const double eps = 1e-10;
const ll LINF = 1001002003004005006ll;
const int INF = 1001001001;
#define dame { puts("-1"); return 0;}
#define yn {puts("YES");}else{puts("NO");}
const int MX = 200005;
vi posx[10010];
vi posy[10010];
int memo[10010];
rep(i,10010){
  memo[i] = -1;
}
int dfs(int pos){
  int maxlength = 0;
  if(memo[pos] != -1){
    rep(i,sz(posy[pos])){
      maxlength = max(maxlength,1 + dfs(posy[pos][i]));
    }
    memo[pos] = maxlength;
  } else {
    maxlength = max(maxlength,memo[pos]);
  }
  return maxlength;
}

int main() {
  int N,M;
  cin >> N >> M;
  rep(i,M) {
    int x,y;
    cin >> x >> y ;
    P p = make_pair(x,y);
    posx[x].pb(y);
    posy[y].pb(x);
  }
  int ans = 0;
  
  srep(i,2,N+1){
    if(sz(posx[i]) == 0){
      rep2(j,sz(posy[i])){
        ans = max(ans,1+ dfs(posy[i][j]));
      }
    }
  }
  cout << ans << endl;
  return 0;
}


Compiler output:
a.cc:4:18: error: expected unqualified-id before 'for'
    4 | #define rep(i,n) for(int i = 0; i < (n); ++i)
      |                  ^~~
a.cc:61:1: note: in expansion of macro 'rep'
   61 | rep(i,10010){
      | ^~~
a.cc:61:5: error: 'i' does not name a type; did you mean 'vi'?
   61 | rep(i,10010){
      |     ^
a.cc:4:33: note: in definition of macro 'rep'
    4 | #define rep(i,n) for(int i = 0; i < (n); ++i)
      |                                 ^
a.cc:4:42: error: expected unqualified-id before '++' token
    4 | #define rep(i,n) for(int i = 0; i < (n); ++i)
      |                                          ^~
a.cc:61:1: note: in expansion of macro 'rep'
   61 | rep(i,10010){
      | ^~~