Language: C++

#include <bits/stdc++.h>
using namespace std;
#define rep(i, n) for (int i = 0; i < (int)(n); i++)
#define rep2(i, n) for (int i = 1; i <= (int)(n); i++)
#define ll long long
#define umap unordered_map
using graph = vector<vector<int>>;
using graph2 = vector<vector<pair<int, int>>>;

ll mod(ll x, ll y){if(x>=0||x%y==0) return x%y;return y+x%y;} //mod including minus
ll dv0(ll x, ll y){if(x>=0||x%y==0)return x/y;return x/y-1;} //rnd down
ll dv1(ll x, ll y){if(x%y==0) return dv0(x,y);return dv0(x,y)+1;} //rnd up
ll M=1e9+7;

int main(){
    int N, M, K;
    cin>>N>>M>>K;
    int check[N];
    int a[N];
    rep(i, N){
        check[i]=0;
    }
    graph G1;//friend
    graph G2;//block
    int a, b;
    rep(i, M){
        cin>>a>>b;
        G1.at(a-1).push_back(b-1);
        G1.at(b-1).push_back(a-1);
    }
    rep(i, K){
        cin>>a>>b;
        G2.at(a-1).push_back(b-1);
        G2.at(b-1).push_back(a-1);
    }
    int c;
    while(true){
        int k=0;
        for(;k<N;k++){
            if(check[k]==0){
                c=k;
                break;
            }
        }
        if(k==N){
            break;
        }
        int count=0;
        queue<int> Q;
        vector<int> V;
        V.push_back(c);
        Q.push(c);
        count++;
        while(!Q.empty()){
            c=Q.front();
            Q.pop();
            rep(i, G1[c].size()){
                if(check[G1[c].at(i)]==0){
                    Q.push(G1[c].at(i));
                    V.push_back(G1[c].at(i));
                    count++;
                    check[G1[c].at(i)]=1;
                }
            }
        }
        rep(j, V.size()){
            a[V.at(j)]=count;
        }
    }
    rep(i, N){
        a[i]-=G1[i].size()+G2[i].size()+1;
    }
}

Compiler output:
a.cc: In function 'int main()':
a.cc:25:9: error: conflicting declaration 'int a'
   25 |     int a, b;
      |         ^
a.cc:19:9: note: previous declaration as 'int a [N]'
   19 |     int a[N];
      |         ^
a.cc:27:12: error: no match for 'operator>>' (operand types are 'std::istream' {aka 'std::basic_istream<char>'} and 'int [N]')
   27 |         cin>>a>>b;
      |         ~~~^~~
      |         |    |
      |         |    int [N]
      |         std::istream {aka std::basic_istream<char>}
In file included from /usr/include/c++/14/sstream:40,
                 from /usr/include/c++/14/complex:45,
                 from /usr/include/c++/14/ccomplex:39,
                 from /usr/include/x86_64-linux-gnu/c++/14/bits/stdc++.h:127,
                 from a.cc:1:
/usr/include/c++/14/istream:170:7: note: candidate: 'std::basic_istream<_CharT, _Traits>::__istream_type& std::basic_istream<_CharT, _Traits>::operator>>(bool&) [with _CharT = char; _Traits = std::char_traits<char>; __istream_type = std::basic_istream<char>]' (near match)
  170 |       operator>>(bool& __n)
      |       ^~~~~~~~
/usr/include/c++/14/istream:170:7: note:   conversion of argument 1 would be ill-formed:
a.cc:27:14: error: cannot bind non-const lvalue reference of type 'bool&' to a value of type 'int*'
   27 |         cin>>a>>b;
      |              ^
/usr/include/c++/14/istream:174:7: note: candidate: 'std::basic_istream<_CharT, _Traits>& std::basic_istream<_CharT, _Traits>::operator>>(short int&) [with _CharT = char; _Traits = std::char_traits<char>]' (near match)
  174 |       operator>>(short& __n);
      |       ^~~~~~~~
/usr/include/c++/14/istream:174:7: note:   conversion of argument 1 would be ill-formed:
a.cc:27:14: error: invalid conversion from 'int*' to 'short int' [-fpermissive]
   27 |         cin>>a>>b;
      |              ^
      |              |
      |              int*
a.cc:27:14: error: cannot bind rvalue '(short int)((int*)(& a))' to 'short int&'
/usr/include/c++/14/istream:177:7: note: candidate: 'std::basic_istream<_CharT, _Traits>::__istream_type& std::basic_istream<_CharT, _Traits>::operator>>(short unsigned int&) [with _CharT = char; _Traits = std::char_traits<char>; __istream_type = std::basic_istream<char>]' (near match)
  177 |       operator>>(unsigned short& __n)
      |       ^~~~~~~~
/usr/include/c++/14/istream:177:7: note:   conversion of argument 1 would be ill-formed:
a.cc:27:14: error: invalid conversion from 'int*' to 'short unsigned int' [-fpermissive]
   27 |         cin>>a>>b;
      |              ^
      |              |
      |              int*
a.cc:27:14: error: cannot bind rvalue '(short unsigned int)((int*)(& a))' to 'short unsigned int&'
/usr/include/c++/14/istream:181:7: note: candidate: 'std::basic_istream<_CharT, _Traits>& std::basic_istream<_CharT, _Traits>::operator>>(int&) [with _CharT = char; _Traits = std::char_traits<char>]' (near match)
  181 |       operator>>(int& __n);
      |       ^~~~~~~~
/usr/include/c++/14/istream:181:7: note:   conversion of argument 1 would be ill-formed:
a.cc:27:14: error: invalid conversion from 'int*' to 'int' [-fpermissive]
   27 |         cin>>a>>b;
      |              ^
      |              |
      |              int*
a.cc:27:14: error: cannot bind rvalue '(int)((int*)(& a))' to 'int&'
/usr/include/c++/14/istream:184:7: note: candidate: 'std::basic_istream<_CharT, _Traits>::__istream_type& std::basic_istream<_CharT, _Traits>::operator>>(unsigned int&) [with _CharT = char; _Traits = std::char_traits<char>; __istream_type = std::basic_istream<char>]' (near match)
  184 |       operator>>(unsigned int& __n)
      |       ^~~~~~~~
/usr/include/c++/14/istream:184:7: note:   conversion of argument 1 would be ill-formed:
a.cc:27:14: error: invalid conversion from 'int*' to 'unsigned int' [-fpermissive]
   27 |         cin>>a>>b;
      |              ^
      |              |
      |              int*
a.cc:27:14: error: cannot bind rvalue '(unsigned int)((int*)(& a))' to 'unsigned int&'
/usr/include/c++/14/istream:188:7: note: candidate: 'std::basic_istream<_CharT, _Traits>::__istream_type& std::basic_istream<_CharT, _Traits>::operator>>(long int&) [with _CharT = char; _Traits = std::char_traits<char>; __istream_type = std::basic_istream<char>]' (near match)
  188 |       operator>>(long& __n)
      |       ^~~~~~~~
/usr/include/c++/14/istream:188:7: note:   conversion of argument 1 would be ill-formed:
a.cc:27:14: error: invalid conversion from 'int*' to 'long int' [-fpermissive]
   27 |         cin>>a>>b;
      |              ^
      |              |
      |              int*
a.cc:27:14: error: cannot bind rvalue '(long int)((int*)(& a))' to 'long int&'
/usr/include/c++/14/istream:192:7: note: candidate: 'std::basic_istream<_CharT, _Traits>::__istream_type& std::basic_istream<_CharT, _Traits>::operator>>(long unsigned int&) [with _CharT = char; _Traits = std::char_traits<char>; __istream_type = std::basic_istream<char>]' (near match)
  192 |       operator>>(unsigned long& __n)
      |       ^~~~~~~~
/usr/include/c++/14/istream:192:7: note:   conversion of argument 1 would be ill-formed:
a.cc:27:14: error: invalid conversion from 'int*' to 'long unsigned int' [-fpermissive]
   27 |         cin>>a>>b;
      |              ^
      |              |
      |              int*
a.cc:27:14: error: cannot bind rvalue '(long unsigned int)((int*)(& a))' to 'long unsigned int&'
/usr/include/c++/14/istream:199:7: note: candidate: 'std::basic_istream<_CharT, _Traits>::__istream_type& std::basic_istream<_CharT, _Traits>::operator>>(long long int&) [with _CharT = char; _Traits = std::char_traits<char>; __istream_type = std::basic_istream<char>]' (near match)
  199 |       operator>>(long long& __n)
      |       ^~~~~~~~
/usr/include/c++/14/istream:199:7: note:   conversion of argument 1 would be ill-formed:
a.cc:27:14: error: invalid conversion from 'int*' to 'long long int' [-fpermissive]
   27 |         cin>>a>>b;
      |              ^
      |              |
      |              int*
a.cc:27:14: error: cannot bind rvalue '(long long int)((int*)(& a))' to 'long long int&'
/usr/include/c++/14/istream:203:7: note: candidate: 'std::basic_istream<_CharT, _Traits>::__istream_type& std::basic_istream<_CharT, _Traits>::operator>>(long long unsigned int&) [with _CharT = char; _Traits = std::char_traits<char>; __istream_type = std::basic_istream<char>]' (near match)
  203 |       operator>>(unsigned long long& __n)
      |       ^~~~~~~~
/usr/include/c++/14/istream:203:7: note:   conversion of argument 1 would be ill-formed:
a.cc:27:14: error: invalid conversion from 'int*' to 'long long unsigned int' [-fpermissive]
   27 |         cin>>a>>b;
      |              ^
      |              |
      |              int*
a.cc:27:14: error: cannot bind rvalue '(long long unsigned int)((int*)(& a))' to 'long long unsigned int&'
/usr/include/c++/14/istream:328:7: note: candidate: 'std::basic_istream<_CharT, _Traits>::__istream_type& std::basic_istream<_CharT, _Traits>::operator>>(void*&) [with _CharT = char; _Traits = std::char_traits<char>; __istream_type = std::basic_istream<char>]' (near match)
  328 |       operator>>(void*& __p)
      |       ^~~~~~~~
/usr/include/c++/14/istream:328:7: note:   conversion of argument 1 would be ill-formed:
a.cc:27:14: error: cannot bind non-const lvalue reference of type 'void*&' to an rvalue of type 'void*'
   27 |         cin>>a>>b;
      |              ^
/usr/include/c++/14/istream:219:7: note: candidate: 'std::basic_istream<_CharT, _Traits>::__istream_type& std::basic_istream<_CharT, _Traits>::operator>>(float&) [with _CharT = char; _Traits = std::char_traits<char>; __istream_type = std::basic_istream<char>]'
  219 |       operator>>(float& __f)
      |       ^~~~~~~~
/usr/include/c++/14/istream:219:25: note:   no known conversion for argument 1 from 'int [N]' to 'float&'
  219 |       operator>>(float& __f)
      |                  ~~~~~~~^~~
/usr/include/c++/14/istream:223:7: note: candidate: 'std::basic_istream<_CharT, _Traits>::__istream_type& std::basic_istream<_CharT, _Traits>::operator>>(double&) [with _CharT = char; _Traits = std::char_traits<char>; __istream_type = std::basic_istream<char>]'
  223 |       operator>>(double& __f)
      |       ^~~~~~~~
/usr/include/c++/14/istream:223:26: note:   no known conversion for argument 1 from 'int [N]' to 'double&'
  223 |       operator>>(double& __f)
      |                  ~~~~~~~~^~~
/usr/include/c++/14/istream:227:7: note: candidate: 'std::basic_istream<_CharT, _Traits>::__istream_type& std::basic_istream<_CharT, _Traits>::operator>>(long double&) [with _CharT = char; _Traits = std::char_traits<char>; __istream_type = std::basic_istream<char>]'
  227 |       operator>>(long double& __f)
      |       ^~~~~~~~
/usr/include/c++/14/istream:227:31: note:   no known conversion for argument 1 from 'int [N]' to 'long double&'
  227 |       operator>>(long double& __f)
      |                  ~~~~~~~~~~~~~^~~
/usr/include/c++/14/istream:122:7: note: candidate: 'std::basic_istream<_CharT, _Traits>::__istream_type& std::basic_istream<_CharT, _Traits>::operator>>(__istream_type& (*)(__istream_type&)) [with _CharT = char; _Traits = std::char_traits<char>; __istream_type = std::basic_istream<char>]'
  122 |       operator>>(__istream_type& (*__pf)(__istream_type&))
      |       ^~~~~~~~
/usr/include/c++/14/istream:122:36: note:   no known conversion for argument 1 from 'int [N]' to 'std::basic_istream<char>::__istream_type& (*)(std::basic_istream<char>::__istream_type&)' {aka 'std::basic_istream<char>& (*)(std::basic_istream<char>&)'}
  122 |       operator>>(__istream_type& (*__pf)(__istream_type&))
      |                  ~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~
/usr/include/c++/14/istream:126:7: note: candidate: 'std::basic_istream<_CharT, _Traits>::__istream_type& std::basic_istream<_CharT, _Traits>::operator>>(__ios_type& (*)(__ios_type&)) [with _CharT = char; _Traits = std::char_traits<char>; __istream_type = std::basic_istream<char>; __ios_type = std::basic_ios<char>]'
  126 |       operator>>(__ios_type& (*__pf)(__ios_type&))
      |       ^~~~~~~~
/usr/include/c++/14/istream:126:32: note:   no known conversion for argument 1