/in/foo.cc: In function 'int main()':
/in/foo.cc:9:15: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for(int i=0;i<s.size();i++)
               ^
/in/foo.cc:10:9: error: no match for 'operator==' (operand types are '__gnu_cxx::__alloc_traits<std::allocator<char> >::value_type {aka char}' and 'std::__cxx11::string {aka std::__cxx11::basic_string<char>}')
  if(s[i]==m) cnt++;
         ^
In file included from /usr/include/c++/5/iosfwd:40:0,
                 from /usr/include/c++/5/ios:38,
                 from /usr/include/c++/5/ostream:38,
                 from /usr/include/c++/5/iostream:39,
                 from /in/foo.cc:1:
/usr/include/c++/5/bits/postypes.h:216:5: note: candidate: template<class _StateT> bool std::operator==(const std::fpos<_StateT>&, const std::fpos<_StateT>&)
     operator==(const fpos<_StateT>& __lhs, const fpos<_StateT>& __rhs)
     ^
/usr/include/c++/5/bits/postypes.h:216:5: note:   template argument deduction/substitution failed:
/in/foo.cc:10:11: note:   mismatched types 'const std::fpos<_StateT>' and '__gnu_cxx::__alloc_traits<std::allocator<char> >::value_type {aka char}'
  if(s[i]==m) cnt++;
           ^
In file included from /usr/include/c++/5/bits/stl_algobase.h:64:0,
                 from /usr/include/c++/5/bits/char_traits.h:39,
                 from /usr/include/c++/5/ios:40,
                 from /usr/include/c++/5/ostream:38,
                 from /usr/include/c++/5/iostream:39,
                 from /in/foo.cc:1:
/usr/include/c++/5/bits/stl_pair.h:214:5: note: candidate: template<class _T1, class _T2> constexpr bool std::operator==(const std::pair<_T1, _T2>&, const std::pair<_T1, _T2>&)
     operator==(const pair<_T1, _T2>& __x, const pair<_T1, _T2>& __y)
     ^
/usr/include/c++/5/bits/stl_pair.h:214:5: note:   template argument deduction/substitution failed:
/in/foo.cc:10:11: note:   mismatched types 'const std::pair<_T1, _T2>' and '__gnu_cxx::__alloc_traits<std::allocator<char> >::value_type {aka char}'
  if(s[i]==m) cnt++;
           ^
In file included from /usr/include/c++/5/bits/stl_algobase.h:67:0,
                 from /usr/include/c++/5/bits/char_traits.h:39,
                 from /usr/include/c++/5/ios:40,
                 from /usr/include/c++/5/ostream:38,
                 from /usr/include/c++/5/iostream:39,
                 from /in/foo.cc:1:
/usr/include/c++/5/bits/stl_iterator.h:292:5: note: candidate: template<class _Iterator> bool std::operator==(const std::reverse_iterator<_Iterator>&, const std::reverse_iterator<_Iterator>&)
     operator==(const reverse_iterator<_Iterator>& __x,
     ^
/usr/include/c++/5/bits/stl_iterator.h:292:5: note:   template argument deduction/substitution failed:
/in/foo.cc:10:11: note:   mismatched types 'const std::reverse_iterator<_Iterator>' and '__gnu_cxx::__alloc_traits<std::allocator<char> >::value_type {aka char}'
  if(s[i]==m) cnt++;
           ^
In file included from /usr/include/c++/5/bits/stl_algobase.h:67:0,
                 from /usr/include/c++/5/bits/char_traits.h:39,
                 from /usr/include/c++/5/ios:40,
                 from /usr/include/c++/5/ostream:38,
                 from /usr/include/c++/5/iostream:39,
                 from /in/foo.cc:1:
/usr/include/c++/5/bits/stl_iterator.h:342:5: note: candidate: template<class _IteratorL, class _IteratorR> bool std::operator==(const std::reverse_iterator<_Iterator>&, const std::reverse_iterator<_IteratorR>&)
     operator==(const reverse_iterator<_IteratorL>& __x,
     ^
/usr/include/c++/5/bits/stl_iterator.h:342:5: note:   template argument deduction/substitution failed:
/in/foo.cc:10:11: note:   mismatched types 'const std::reverse_iterator<_Iterator>' and '__gnu_cxx::__alloc_traits<std::allocator<char> >::value_type {aka char}'
  if(s[i]==m) cnt++;
           ^
In file included from /usr/include/c++/5/bits/stl_algobase.h:67:0,
                 from /usr/include/c++/5/bits/char_traits.h:39,
                 from /usr/include/c++/5/ios:40,
                 from /usr/include/c++/5/ostream:38,
                 from /usr/include/c++/5/iostream:39,
                 from /in/foo.cc:1:
/usr/include/c++/5/bits/stl_iterator.h:1065:5: note: candidate: template<class _IteratorL, class _IteratorR> bool std::operator==(const std::move_iterator<_Iterator>&, const std::move_iterator<_IteratorR>&)
     operator==(const move_iterator<_IteratorL>& __x,
     ^
/usr/include/c++/5/bits/stl_iterator.h:1065:5: note:   template argument deduction/substitution failed:
/in/foo.cc:10:11: note:   mismatched types 'const std::move_iterator<_Iterator>' and '__gnu_cxx::__alloc_traits<std::allocator<char> >::value_type {aka char}'
  if(s[i]==m) cnt++;
           ^
In file included from /usr/include/c++/5/bits/stl_algobase.h:67:0,
                 from /usr/include/c++/5/bits/char_traits.h:39,
                 from /usr/include/c++/5/ios:40,
                 from /usr/include/c++/5/ostream:38,
                 from /usr/include/c++/5/iostream:39,
                 from /in/foo.cc:1:
/usr/include/c++/5/bits/stl_iterator.h:1071:5: note: candidate: template<class _Iterator> bool std::operator==(const std::move_iterator<_Iterator>&, const std::move_iterator<_Iterator>&)
     operator==(const move_iterator<_Iterator>& __x,
     ^
/usr/include/c++/5/bits/stl_iterator.h:1071:5: note:   template argument deduction/substitution failed:
/in/foo.cc:10:11: note:   mismatched types 'const std::move_iterator<_Iterator>' and '__gnu_cxx::__alloc_traits<std::allocator<char> >::value_type {aka char}'
  if(s[i]==m) cnt++;
           ^
In file included from /usr/include/c++/5/string:41:0,
                 from /usr/include/c++/5/bits/locale_classes.h:40,
                 from /usr/include/c++/5/bits/ios_base.h:41,
                 from /usr/include/c++/5/ios:42,
                 from /usr/include/c++/5/ostream:38,
                 from /usr/include/c++/5/iostream:39,
                 from /in/foo.cc:1:
/usr/include/c++/5/bits/allocator.h:128:5: note: candidate: template<class _T1, class _T2> bool std::operator==(const std::allocator<_CharT>&, const std::allocator<_T2>&)
     operator==(const allocator<_T1>&, const allocator<_T2>&)
     ^
/usr/include/c++/5/bits/allocator.h:128:5: note:   template argument deduction/substitution failed:
/in/foo.cc:10:11: note:   mismatched types 'const std::allocator<_CharT>' and '__gnu_cxx::__alloc_traits<std::allocator<char> >::value_type {aka char}'
  if(s[i]==m) cnt++;
           ^
In file included from /usr/include/c++/5/string:41:0,
                 from /usr/include/c++/5/bits/locale_classes.h:40,
                 from /usr/include/c++/5/bits/ios_base.h:41,
                 from /usr/include/c++/5/ios:42,
                 from /usr/include/c++/5/ostream:38,
                 from /usr/include/c++/5/iostream:39,
                 from /in/foo.cc:1:
/usr/include/c++/5/bits/allocator.h:134:5: note: candidate: template<class _Tp> bool std::operator==(const std::allocator<_CharT>&, const std::allocator<_CharT>&)
     operator==(const allocator<_Tp>&, const allocator<_Tp>&)
     ^
/usr/include/c++/5/bits/allocator.h:134:5: note:   template argument deduction/substitution failed:
/in/foo.cc:10:11: note:   mismatched types 'const std::allocator<_CharT>' and '__gnu_cxx::__alloc_traits<std::allocator<char> >::value_type {aka char}'
  if(s[i]==m) cnt++;
           ^
In file included from /usr/include/c++/5/string:52:0,
                 from /usr/include/c++/5/bits/locale_classes.h:40,
                 from /usr/include/c++/5/bits/ios_base.h:41,
                 from /usr/include/c++/5/ios:42,
                 from /usr/include/c++/5/ostream:38,
                 from /usr/include/c++/5/iostream:39,
                 from /in/foo.cc:1:
/usr/include/c++/5/bits/basic_string.h:4904:5: note: candidate: template<class _CharT, class _Traits, class _Alloc> bool std::operator==(const std::__cxx11::basic_string<_CharT, _Traits, _Alloc>&, const std::__cxx11::basic_string<_CharT, _Traits, _Alloc>&)
     operator==(const basic_string<_CharT, _Traits, _Alloc>& __lhs,
     ^
/usr/include/c++/5/bits/basic_string.h:4904:5: note:   template argument deduction/substitution failed:
/in/foo.