Language: C++

#include<iostream>
#include<map>
#include<cstdio>
using namespace std;
int main(){
	bool month = false;
	map<int, pair<int, int> > com;
	int n;
	char s[50];
	while(cin.getline(s,50)){
		if(s == 0){month = true;continue;}
		sscanf(s,"%d,%*d",&n);
		if(!month){com[n].first = 1;}
		else if(month && com[n].first){com[n].first = 2;}
		com[n].second ++;
	}
	for(__typeof(com.begin()) i=com.begin(); i<com.end(); i++){
		if(i->second.first == 2){
			cout << i->first << " " << i->second.second <<endl;
		}
	}
	return 0;
}

Compiler output:
a.cc: In function 'int main()':
a.cc:17:51: error: no match for 'operator<' (operand types are 'std::map<int, std::pair<int, int> >::iterator' {aka 'std::_Rb_tree<int, std::pair<const int, std::pair<int, int> >, std::_Select1st<std::pair<const int, std::pair<int, int> > >, std::less<int>, std::allocator<std::pair<const int, std::pair<int, int> > > >::iterator'} and 'std::map<int, std::pair<int, int> >::iterator' {aka 'std::_Rb_tree<int, std::pair<const int, std::pair<int, int> >, std::_Select1st<std::pair<const int, std::pair<int, int> > >, std::less<int>, std::allocator<std::pair<const int, std::pair<int, int> > > >::iterator'})
   17 |         for(__typeof(com.begin()) i=com.begin(); i<com.end(); i++){
      |                                                  ~^~~~~~~~~~
      |                                                  |        |
      |                                                  |        _Rb_tree_iterator<[...]>
      |                                                  _Rb_tree_iterator<[...]>
In file included from /usr/include/c++/14/string:48,
                 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_iterator.h:448:5: note: candidate: 'template<class _Iterator> constexpr bool std::operator<(const reverse_iterator<_Iterator>&, const reverse_iterator<_Iterator>&)'
  448 |     operator<(const reverse_iterator<_Iterator>& __x,
      |     ^~~~~~~~
/usr/include/c++/14/bits/stl_iterator.h:448:5: note:   template argument deduction/substitution failed:
a.cc:17:60: note:   'std::map<int, std::pair<int, int> >::iterator' {aka 'std::_Rb_tree<int, std::pair<const int, std::pair<int, int> >, std::_Select1st<std::pair<const int, std::pair<int, int> > >, std::less<int>, std::allocator<std::pair<const int, std::pair<int, int> > > >::iterator'} is not derived from 'const std::reverse_iterator<_Iterator>'
   17 |         for(__typeof(com.begin()) i=com.begin(); i<com.end(); i++){
      |                                                            ^
/usr/include/c++/14/bits/stl_iterator.h:493:5: note: candidate: 'template<class _IteratorL, class _IteratorR> constexpr bool std::operator<(const reverse_iterator<_Iterator>&, const reverse_iterator<_IteratorR>&)'
  493 |     operator<(const reverse_iterator<_IteratorL>& __x,
      |     ^~~~~~~~
/usr/include/c++/14/bits/stl_iterator.h:493:5: note:   template argument deduction/substitution failed:
a.cc:17:60: note:   'std::map<int, std::pair<int, int> >::iterator' {aka 'std::_Rb_tree<int, std::pair<const int, std::pair<int, int> >, std::_Select1st<std::pair<const int, std::pair<int, int> > >, std::less<int>, std::allocator<std::pair<const int, std::pair<int, int> > > >::iterator'} is not derived from 'const std::reverse_iterator<_Iterator>'
   17 |         for(__typeof(com.begin()) i=com.begin(); i<com.end(); i++){
      |                                                            ^
/usr/include/c++/14/bits/stl_iterator.h:1694:5: note: candidate: 'template<class _IteratorL, class _IteratorR> constexpr bool std::operator<(const move_iterator<_IteratorL>&, const move_iterator<_IteratorR>&)'
 1694 |     operator<(const move_iterator<_IteratorL>& __x,
      |     ^~~~~~~~
/usr/include/c++/14/bits/stl_iterator.h:1694:5: note:   template argument deduction/substitution failed:
a.cc:17:60: note:   'std::map<int, std::pair<int, int> >::iterator' {aka 'std::_Rb_tree<int, std::pair<const int, std::pair<int, int> >, std::_Select1st<std::pair<const int, std::pair<int, int> > >, std::less<int>, std::allocator<std::pair<const int, std::pair<int, int> > > >::iterator'} is not derived from 'const std::move_iterator<_IteratorL>'
   17 |         for(__typeof(com.begin()) i=com.begin(); i<com.end(); i++){
      |                                                            ^
/usr/include/c++/14/bits/stl_iterator.h:1760:5: note: candidate: 'template<class _Iterator> constexpr bool std::operator<(const move_iterator<_IteratorL>&, const move_iterator<_IteratorL>&)'
 1760 |     operator<(const move_iterator<_Iterator>& __x,
      |     ^~~~~~~~
/usr/include/c++/14/bits/stl_iterator.h:1760:5: note:   template argument deduction/substitution failed:
a.cc:17:60: note:   'std::map<int, std::pair<int, int> >::iterator' {aka 'std::_Rb_tree<int, std::pair<const int, std::pair<int, int> >, std::_Select1st<std::pair<const int, std::pair<int, int> > >, std::less<int>, std::allocator<std::pair<const int, std::pair<int, int> > > >::iterator'} is not derived from 'const std::move_iterator<_IteratorL>'
   17 |         for(__typeof(com.begin()) i=com.begin(); i<com.end(); i++){
      |                                                            ^
In file included from /usr/include/c++/14/bits/stl_algobase.h:64,
                 from /usr/include/c++/14/string:51:
/usr/include/c++/14/bits/stl_pair.h:1045:5: note: candidate: 'template<class _T1, class _T2> constexpr bool std::operator<(const pair<_T1, _T2>&, const pair<_T1, _T2>&)'
 1045 |     operator<(const pair<_T1, _T2>& __x, const pair<_T1, _T2>& __y)
      |     ^~~~~~~~
/usr/include/c++/14/bits/stl_pair.h:1045:5: note:   template argument deduction/substitution failed:
a.cc:17:60: note:   'std::map<int, std::pair<int, int> >::iterator' {aka 'std::_Rb_tree<int, std::pair<const int, std::pair<int, int> >, std::_Select1st<std::pair<const int, std::pair<int, int> > >, std::less<int>, std::allocator<std::pair<const int, std::pair<int, int> > > >::iterator'} is not derived from 'const std::pair<_T1, _T2>'
   17 |         for(__typeof(com.begin()) i=com.begin(); i<com.end(); i++){
      |                                                            ^
In file included from /usr/include/c++/14/bits/basic_string.h:47,
                 from /usr/include/c++/14/string:54:
/usr/include/c++/14/string_view:673:5: note: candidate: 'template<class _CharT, class _Traits> constexpr bool std::operator<(basic_string_view<_CharT, _Traits>, basic_string_view<_CharT, _Traits>)'
  673 |     operator< (basic_string_view<_CharT, _Traits> __x,
      |     ^~~~~~~~
/usr/include/c++/14/string_view:673:5: note:   template argument deduction/substitution failed:
a.cc:17:60: note:   'std::_Rb_tree_iterator<std::pair<const int, std::pair<int, int> > >' is not derived from 'std::basic_string_view<_CharT, _Traits>'
   17 |         for(__typeof(com.begin()) i=com.begin(); i<com.end(); i++){
      |                                                            ^
/usr/include/c++/14/string_view:680:5: note: candidate: 'template<class _CharT, class _Traits> constexpr bool std::operator<(basic_string_view<_CharT, _Traits>, __type_identity_t<basic_string_view<_CharT, _Traits> >)'
  680 |     operator< (basic_string_view<_CharT, _Traits> __x,
      |     ^~~~~~~~
/usr/include/c++/14/string_view:680:5: note:   template argument deduction/substitution failed:
a.cc:17:60: note:   'std::_Rb_tree_iterator<std::pair<const int, std::pair<int, int> > >' is not derived from 'std::basic_string_view<_CharT, _Traits>'
   17 |         for(__typeof(com.begin()) i=com.begin(); i<com.end(); i++){
      |                                                            ^
/usr/include/c++/14/string_view:688:5: note: candidate: 'template<class _CharT, class _Traits> constexpr bool std::operator<(__type_identity_t<basic_string_view<_CharT, _Traits> >, basic_string_view<_CharT, _Traits>)'
  688 |     operator< (__type_identity_t<basic_string_view<_CharT, _Traits>> __x,
      |     ^~~~~~~~
/usr/include/c++/14/string_view:688:5: note:   template argument deduction/substitution failed:
a.cc:17:60: note:   'std::_Rb_tree_iterator<std::pair<const int, std::pair<int, int> > >' is not derived from 'std::basic_string_view<_CharT, _Traits>'
   17 |         for(__typeof(com.begin()) i=com.begin(); i<com.end(); i++){
      |                                                            ^
/usr/include/c++/14/bits/basic_string.h:3874:5: note: candidate: 'template<class _CharT, class _Traits, class _Alloc> bool std::operator<(const __cxx11::basic_string<_CharT, _Traits, _Allocator>&, const __cxx11::basic_string<_CharT, _Traits, _Allocator>&)'
 3874 |     operator<(const basic_string<_CharT, _Traits, _Alloc>& __lhs,
      |     ^~~~~~~~
/usr/include/c++/14/bits/basic_string.h:3874:5: note:   template argument deduction/substitution failed:
a.cc:17:60: note:   'std::map<int, std::pair<int, int> >::iterator' {aka 'std::_Rb_tree<int, std::pair<const int, std::pair<int, int> >, std::_Select1st<std::pair<const int, std::pair<int, int> > >, std::less<int>, std::allocator<std::pair<const int, std::pair<int, int> > > >::iterator'} is not derived from 'const std::__cxx11::basic_string<_CharT, _Traits, _Allocator>'
   17 |         for(__typeof(com.begin()) i=com.begin(); i<com.end(); i++){
      |                                                            ^
/usr/include/c++/14/bits/basic_string.h:3888:5: note: candidate: 'template<class _CharT, class _Traits, class _Alloc> bool std::operator<(const __cxx11::basic_string<_CharT, _Traits, _Allocator>&, const _CharT*)'
 3888 |     operator<(const basic_string<_CharT, _Traits, _Alloc>& __lhs,
      |     ^~~~~~~~
/usr/include/c++/14/bits/basic_string.h:3888:5: note:   template argument deduction/substitution failed:
a.cc:17:60: note:   'std::map<int, std::pair<int, int> >::iterator' {aka 'std::_Rb_tree<int, std::pair<const int, std::pair<int, int> >, std::_Select1st<std::pair<const int, std::pair<int, int> > >, std::less<int>, std::allocator<std::pair<const int, std::pair<int, int> > > >::iterator'} is not derived from 'const std::__cxx11::basic_string<_CharT, _Traits, _Allocator>'
   17 |         for(__typeof(com.begin()) i=com.begin(); i<com.end(); i++){
      |                                                            ^
/usr/include/c++/14/bits/basic_string.h:3901:5: note: candidate: 'template<class _CharT, class _Traits, class _Alloc> bool std::operator<(const _CharT*, const __cxx11::basic_string<_CharT, _Traits, _Allocator>&)'
 3901 |     operator<(c