/in/foo.cc:3:1: error: 'vector' does not name a type
 vector<int>num;
 ^~~~~~
/in/foo.cc: In function 'int main()':
/in/foo.cc:7:2: error: 'cin' was not declared in this scope
  cin>>n;
  ^~~
/in/foo.cc:7:2: note: suggested alternative:
In file included from /in/foo.cc:1:0:
/usr/include/c++/6/iostream:60:18: note:   'std::cin'
   extern istream cin;  /// Linked to standard input
                  ^~~
/in/foo.cc:11:32: error: 'num' was not declared in this scope
   for(int j=a[i]+1;j<=b[i];j++)num.push(j);
                                ^~~
/in/foo.cc:13:11: error: 'num' was not declared in this scope
  int size=num.size();
           ^~~
/in/foo.cc:14:19: error: 'sort' was not declared in this scope
  sort(num,num+size);
                   ^
/in/foo.cc:19:2: error: 'cout' was not declared in this scope
  cout<<countn;
  ^~~~
/in/foo.cc:19:2: note: suggested alternative:
In file included from /in/foo.cc:1:0:
/usr/include/c++/6/iostream:61:18: note:   'std::cout'
   extern ostream cout;  /// Linked to standard output
                  ^~~~