/in/foo.cc: In function 'void DFS(int, std::__cxx11::string)':
/in/foo.cc:56:33: error: no matching function for call to 'std::__cxx11::basic_string<char>::basic_string(char&)'
    tmp=str+(std::string)(c[i][0]);
                                 ^
In file included from /usr/include/c++/7/string:52:0,
                 from /in/foo.cc:2:
/usr/include/c++/7/bits/basic_string.h:588:9: note: candidate: template<class _InputIterator, class> std::__cxx11::basic_string<_CharT, _Traits, _Alloc>::basic_string(_InputIterator, _InputIterator, const _Alloc&)
         basic_string(_InputIterator __beg, _InputIterator __end,
         ^~~~~~~~~~~~
/usr/include/c++/7/bits/basic_string.h:588:9: note:   template argument deduction/substitution failed:
/in/foo.cc:56:33: note:   candidate expects 3 arguments, 1 provided
    tmp=str+(std::string)(c[i][0]);
                                 ^
In file included from /usr/include/c++/7/string:52:0,
                 from /in/foo.cc:2:
/usr/include/c++/7/bits/basic_string.h:550:7: note: candidate: std::__cxx11::basic_string<_CharT, _Traits, _Alloc>::basic_string(std::__cxx11::basic_string<_CharT, _Traits, _Alloc>&&, const _Alloc&) [with _CharT = char; _Traits = std::char_traits<char>; _Alloc = std::allocator<char>]
       basic_string(basic_string&& __str, const _Alloc& __a)
       ^~~~~~~~~~~~
/usr/include/c++/7/bits/basic_string.h:550:7: note:   candidate expects 2 arguments, 1 provided
/usr/include/c++/7/bits/basic_string.h:546:7: note: candidate: std::__cxx11::basic_string<_CharT, _Traits, _Alloc>::basic_string(const std::__cxx11::basic_string<_CharT, _Traits, _Alloc>&, const _Alloc&) [with _CharT = char; _Traits = std::char_traits<char>; _Alloc = std::allocator<char>]
       basic_string(const basic_string& __str, const _Alloc& __a)
       ^~~~~~~~~~~~
/usr/include/c++/7/bits/basic_string.h:546:7: note:   candidate expects 2 arguments, 1 provided
/usr/include/c++/7/bits/basic_string.h:542:7: note: candidate: std::__cxx11::basic_string<_CharT, _Traits, _Alloc>::basic_string(std::initializer_list<_Tp>, const _Alloc&) [with _CharT = char; _Traits = std::char_traits<char>; _Alloc = std::allocator<char>]
       basic_string(initializer_list<_CharT> __l, const _Alloc& __a = _Alloc())
       ^~~~~~~~~~~~
/usr/include/c++/7/bits/basic_string.h:542:7: note:   no known conversion for argument 1 from 'char' to 'std::initializer_list<char>'
/usr/include/c++/7/bits/basic_string.h:515:7: note: candidate: std::__cxx11::basic_string<_CharT, _Traits, _Alloc>::basic_string(std::__cxx11::basic_string<_CharT, _Traits, _Alloc>&&) [with _CharT = char; _Traits = std::char_traits<char>; _Alloc = std::allocator<char>]
       basic_string(basic_string&& __str) noexcept
       ^~~~~~~~~~~~
/usr/include/c++/7/bits/basic_string.h:515:7: note:   no known conversion for argument 1 from 'char' to 'std::__cxx11::basic_string<char>&&'
/usr/include/c++/7/bits/basic_string.h:503:7: note: candidate: std::__cxx11::basic_string<_CharT, _Traits, _Alloc>::basic_string(std::__cxx11::basic_string<_CharT, _Traits, _Alloc>::size_type, _CharT, const _Alloc&) [with _CharT = char; _Traits = std::char_traits<char>; _Alloc = std::allocator<char>; std::__cxx11::basic_string<_CharT, _Traits, _Alloc>::size_type = long unsigned int]
       basic_string(size_type __n, _CharT __c, const _Alloc& __a = _Alloc())
       ^~~~~~~~~~~~
/usr/include/c++/7/bits/basic_string.h:503:7: note:   candidate expects 3 arguments, 1 provided
/usr/include/c++/7/bits/basic_string.h:493:7: note: candidate: std::__cxx11::basic_string<_CharT, _Traits, _Alloc>::basic_string(const _CharT*, const _Alloc&) [with _CharT = char; _Traits = std::char_traits<char>; _Alloc = std::allocator<char>] <near match>
       basic_string(const _CharT* __s, const _Alloc& __a = _Alloc())
       ^~~~~~~~~~~~
/usr/include/c++/7/bits/basic_string.h:493:7: note:   conversion of argument 1 would be ill-formed:
/in/foo.cc:56:32: error: invalid conversion from 'char' to 'const char*' [-fpermissive]
    tmp=str+(std::string)(c[i][0]);
                         ~~~~~~~^~
In file included from /usr/include/c++/7/string:52:0,
                 from /in/foo.cc:2:
/usr/include/c++/7/bits/basic_string.h:483:7: note: candidate: std::__cxx11::basic_string<_CharT, _Traits, _Alloc>::basic_string(const _CharT*, std::__cxx11::basic_string<_CharT, _Traits, _Alloc>::size_type, const _Alloc&) [with _CharT = char; _Traits = std::char_traits<char>; _Alloc = std::allocator<char>; std::__cxx11::basic_string<_CharT, _Traits, _Alloc>::size_type = long unsigned int]
       basic_string(const _CharT* __s, size_type __n,
       ^~~~~~~~~~~~
/usr/include/c++/7/bits/basic_string.h:483:7: note:   candidate expects 3 arguments, 1 provided
/usr/include/c++/7/bits/basic_string.h:465:7: note: candidate: std::__cxx11::basic_string<_CharT, _Traits, _Alloc>::basic_string(const std::__cxx11::basic_string<_CharT, _Traits, _Alloc>&, std::__cxx11::basic_string<_CharT, _Traits, _Alloc>::size_type, std::__cxx11::basic_string<_CharT, _Traits, _Alloc>::size_type, const _Alloc&) [with _CharT = char; _Traits = std::char_traits<char>; _Alloc = std::allocator<char>; std::__cxx11::basic_string<_CharT, _Traits, _Alloc>::size_type = long unsigned int]
       basic_string(const basic_string& __str, size_type __pos,
       ^~~~~~~~~~~~
/usr/include/c++/7/bits/basic_string.h:465:7: note:   candidate expects 4 arguments, 1 provided
/usr/include/c++/7/bits/basic_string.h:449:7: note: candidate: std::__cxx11::basic_string<_CharT, _Traits, _Alloc>::basic_string(const std::__cxx11::basic_string<_CharT, _Traits, _Alloc>&, std::__cxx11::basic_string<_CharT, _Traits, _Alloc>::size_type, std::__cxx11::basic_string<_CharT, _Traits, _Alloc>::size_type) [with _CharT = char; _Traits = std::char_traits<char>; _Alloc = std::allocator<char>; std::__cxx11::basic_string<_CharT, _Traits, _Alloc>::size_type = long unsigned int]
       basic_string(const basic_string& __str, size_type __pos,
       ^~~~~~~~~~~~
/usr/include/c++/7/bits/basic_string.h:449:7: note:   candidate expects 3 arguments, 1 provided
/usr/include/c++/7/bits/basic_string.h:434:7: note: candidate: std::__cxx11::basic_string<_CharT, _Traits, _Alloc>::basic_string(const std::__cxx11::basic_string<_CharT, _Traits, _Alloc>&, std::__cxx11::basic_string<_CharT, _Traits, _Alloc>::size_type, const _Alloc&) [with _CharT = char; _Traits = std::char_traits<char>; _Alloc = std::allocator<char>; std::__cxx11::basic_string<_CharT, _Traits, _Alloc>::size_type = long unsigned int]
       basic_string(const basic_string& __str, size_type __pos,
       ^~~~~~~~~~~~
/usr/include/c++/7/bits/basic_string.h:434:7: note:   candidate expects 3 arguments, 1 provided
/usr/include/c++/7/bits/basic_string.h:421:7: note: candidate: std::__cxx11::basic_string<_CharT, _Traits, _Alloc>::basic_string(const std::__cxx11::basic_string<_CharT, _Traits, _Alloc>&) [with _CharT = char; _Traits = std::char_traits<char>; _Alloc = std::allocator<char>]
       basic_string(const basic_string& __str)
       ^~~~~~~~~~~~
/usr/include/c++/7/bits/basic_string.h:421:7: note:   no known conversion for argument 1 from 'char' to 'const std::__cxx11::basic_string<char>&'
/usr/include/c++/7/bits/basic_string.h:413:7: note: candidate: std::__cxx11::basic_string<_CharT, _Traits, _Alloc>::basic_string(const _Alloc&) [with _CharT = char; _Traits = std::char_traits<char>; _Alloc = std::allocator<char>]
       basic_string(const _Alloc& __a) _GLIBCXX_NOEXCEPT
       ^~~~~~~~~~~~
/usr/include/c++/7/bits/basic_string.h:413:7: note:   no known conversion for argument 1 from 'char' to 'const std::allocator<char>&'
/usr/include/c++/7/bits/basic_string.h:404:7: note: candidate: std::__cxx11::basic_string<_CharT, _Traits, _Alloc>::basic_string() [with _CharT = char; _Traits = std::char_traits<char>; _Alloc = std::allocator<char>]
       basic_string()
       ^~~~~~~~~~~~
/usr/include/c++/7/bits/basic_string.h:404:7: note:   candidate expects 0 arguments, 1 provided