Main.cc: In function ‘int main()’: Main.cc:19:25: error: no match for ‘operator<<’ (operand types are ‘std::basic_ostream’ and ‘’) cout<::__ostream_type& std::basic_ostream<_CharT, _Traits>::operator<<(std::basic_ostream<_CharT, _Traits>::__ostream_type& (*)(std::basic_ostream<_CharT, _Traits>::__ostream_type&)) [with _CharT = char; _Traits = std::char_traits; std::basic_ostream<_CharT, _Traits>::__ostream_type = std::basic_ostream] operator<<(__ostream_type& (*__pf)(__ostream_type&)) ^~~~~~~~ /usr/include/c++/7/ostream:108:7: note: no known conversion for argument 1 from ‘’ to ‘std::basic_ostream::__ostream_type& (*)(std::basic_ostream::__ostream_type&) {aka std::basic_ostream& (*)(std::basic_ostream&)}’ /usr/include/c++/7/ostream:117:7: note: candidate: std::basic_ostream<_CharT, _Traits>::__ostream_type& std::basic_ostream<_CharT, _Traits>::operator<<(std::basic_ostream<_CharT, _Traits>::__ios_type& (*)(std::basic_ostream<_CharT, _Traits>::__ios_type&)) [with _CharT = char; _Traits = std::char_traits; std::basic_ostream<_CharT, _Traits>::__ostream_type = std::basic_ostream; std::basic_ostream<_CharT, _Traits>::__ios_type = std::basic_ios] operator<<(__ios_type& (*__pf)(__ios_type&)) ^~~~~~~~ /usr/include/c++/7/ostream:117:7: note: no known conversion for argument 1 from ‘’ to ‘std::basic_ostream::__ios_type& (*)(std::basic_ostream::__ios_type&) {aka std::basic_ios& (*)(std::basic_ios&)}’ /usr/include/c++/7/ostream:127:7: note: candidate: std::basic_ostream<_CharT, _Traits>::__ostream_type& std::basic_ostream<_CharT, _Traits>::operator<<(std::ios_base& (*)(std::ios_base&)) [with _CharT = char; _Traits = std::char_traits; std::basic_ostream<_CharT, _Traits>::__ostream_type = std::basic_ostream] operator<<(ios_base& (*__pf) (ios_base&)) ^~~~~~~~ /usr/include/c++/7/ostream:127:7: note: no known conversion for argument 1 from ‘’ to ‘std::ios_base& (*)(std::ios_base&)’ /usr/include/c++/7/ostream:166:7: note: candidate: std::basic_ostream<_CharT, _Traits>::__ostream_type& std::basic_ostream<_CharT, _Traits>::operator<<(long int) [with _CharT = char; _Traits = std::char_traits; std::basic_ostream<_CharT, _Traits>::__ostream_type = std::basic_ostream] operator<<(long __n) ^~~~~~~~ /usr/include/c++/7/ostream:166:7: note: no known conversion for argument 1 from ‘’ to ‘long int’ /usr/include/c++/7/ostream:170:7: note: candidate: std::basic_ostream<_CharT, _Traits>::__ostream_type& std::basic_ostream<_CharT, _Traits>::operator<<(long unsigned int) [with _CharT = char; _Traits = std::char_traits; std::basic_ostream<_CharT, _Traits>::__ostream_type = std::basic_ostream] operator<<(unsigned long __n) ^~~~~~~~ /usr/include/c++/7/ostream:170:7: note: no known conversion for argument 1 from ‘’ to ‘long unsigned int’ /usr/include/c++/7/ostream:174:7: note: candidate: std::basic_ostream<_CharT, _Traits>::__ostream_type& std::basic_ostream<_CharT, _Traits>::operator<<(bool) [with _CharT = char; _Traits = std::char_traits; std::basic_ostream<_CharT, _Traits>::__ostream_type = std::basic_ostream] operator<<(bool __n) ^~~~~~~~ /usr/include/c++/7/ostream:174:7: note: no known conversion for argument 1 from ‘’ to ‘bool’ In file included from /usr/include/c++/7/ostream:693:0, from /usr/include/c++/7/istream:39, from /usr/include/c++/7/sstream:38, from /usr/include/c++/7/complex:45, from /usr/include/c++/7/ccomplex:39, from /usr/include/x86_64-linux-gnu/c++/7/bits/stdc++.h:52, from Main.cc:1: /usr/include/c++/7/bits/ostream.tcc:91:5: note: candidate: std::basic_ostream<_CharT, _Traits>& std::basic_ostream<_CharT, _Traits>::operator<<(short int) [with _CharT = char; _Traits = std::char_traits] basic_ostream<_CharT, _Traits>:: ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ /usr/include/c++/7/bits/ostream.tcc:91:5: note: no known conversion for argument 1 from ‘’ to ‘short int’ In file included from /usr/include/c++/7/istream:39:0, from /usr/include/c++/7/sstream:38, from /usr/include/c++/7/complex:45, from /usr/include/c++/7/ccomplex:39, from /usr/include/x86_64-linux-gnu/c++/7/bits/stdc++.h:52, from Main.cc:1: /usr/include/c++/7/ostream:181:7: note: candidate: std::basic_ostream<_CharT, _Traits>::__ostream_type& std::basic_ostream<_CharT, _Traits>::operator<<(short unsigned int) [with _CharT = char; _Traits = std::char_traits; std::basic_ostream<_CharT, _Traits>::__ostream_type = std::basic_ostream] operator<<(unsigned short __n) ^~~~~~~~ /usr/include/c++/7/ostream:181:7: note: no known conversion for argument 1 from ‘’ to ‘short unsigned int’ In file included from /usr/include/c++/7/ostream:693:0, from /usr/include/c++/7/istream:39, from /usr/include/c++/7/sstream:38, from /usr/include/c++/7/complex:45, from /usr/include/c++/7/ccomplex:39, from /usr/include/x86_64-linux-gnu/c++/7/bits/stdc++.h:52, from Main.cc:1: /usr/include/c++/7/bits/ostream.tcc:105:5: note: candidate: std::basic_ostream<_CharT, _Traits>& std::basic_ostream<_CharT, _Traits>::operator<<(int) [with _CharT = char; _Traits = std::char_traits] basic_ostream<_CharT, _Traits>:: ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ /usr/include/c++/7/bits/ostream.tcc:105:5: note: no known conversion for argument 1 from ‘’ to ‘int’ In file included from /usr/include/c++/7/istream:39:0, from /usr/include/c++/7/sstream:38, from /usr/include/c++/7/complex:45, from /usr/include/c++/7/ccomplex:39, from /usr/include/x86_64-linux-gnu/c++/7/bits/stdc++.h:52, from Main.cc:1: /usr/include/c++/7/ostream:192:7: note: candidate: std::basic_ostream<_CharT, _Traits>::__ostream_type& std::basic_ostream<_CharT, _Traits>::operator<<(unsigned int) [with _CharT = char; _Traits = std::char_traits; std::basic_ostream<_CharT, _Traits>::__ostream_type = std::basic_ostream] operator<<(unsigned int __n) ^~~~~~~~ /usr/include/c++/7/ostream:192:7: note: no known conversion for argument 1 from ‘’ to ‘unsigned int’ /usr/include/c++/7/ostream:201:7: note: candidate: std::basic_ostream<_CharT, _Traits>::__ostream_type& std::basic_ostream<_CharT, _Traits>::operator<<(long long int) [with _CharT = char; _Traits = std::char_traits; std::basic_ostream<_CharT, _Traits>::__ostream_type = std::basic_ostream] operator<<(long long __n) ^~~~~~~~ /usr/include/c++/7/ostream:201:7: note: no known conversion for argument 1 from ‘’ to ‘long long int’ /usr/include/c++/7/ostream:205:7: note: candidate: std::basic_ostream<_CharT, _Traits>::__ostream_type& std::basic_ostream<_CharT, _Traits>::operator<<(long long unsigned int) [with _CharT = char; _Traits = std::char_traits; std::basic_ostream<_CharT, _Traits>::__ostream_type = std::basic_ostream] operator<<(unsigned long long __n) ^~~~~~~~ /usr/include/c++/7/ostream:205:7: note: no known conversion for argument 1 from ‘’ to ‘long long unsigned int’ /usr/include/c++/7/ostream:220:7: note: candidate: std::basic_ostream<_CharT, _Traits>::__ostream_type& std::basic_ostream<_CharT, _Traits>::operator<<(double) [with _CharT = char; _Traits = std::char_traits; std::basic_ostream<_CharT, _Traits>::__ostream_type = std::basic_ostream] operator<<(double __f) ^~~~~~~~ /usr/include/c++/7/ostream:220:7: note: no known conversion for argument 1 from ‘’ to ‘double’ /usr/include/c++/7/ostream:224:7: note: candidate: std::basic_ostream<_CharT, _Traits>::__ostream_type& std::basic_ostream<_CharT, _Traits>::operator<<(float) [with _CharT = char; _Traits = std::char_traits; std::basic_ostream<_CharT, _Traits>::__ostream_type = std::basic_ostream] operator<<(float __f) ^~~~~~~~ /usr/include/c++/7/ostream:224:7: note: no known conversion for argument 1 from ‘’ to ‘float’ /usr/include/c++/7/ostream:232:7: note: candidate: std::basic_ostream<_CharT, _Traits>::__ostream_type& std::basic_ostream<_CharT, _Traits>::operator<<(long double) [with _CharT = char; _Traits = std::char_traits; std::basic_ostream<_CharT, _Traits>::__ostream_type = std::basic_ostream] operator<<(long double __f) ^~~~~~~~ /usr/include/c++/7/ostream:232:7: note: no known conversion for argument 1 from ‘’ to ‘long double’ /usr/include/c++/7/ostream:245:7: note: candidate: std::basic_ostream<_CharT, _Traits>::__ostream_type& std::basic_ostream<_CharT, _Traits>::operator<<(const void*) [with _CharT = char; _Traits = std::char_traits; std::basic_ostream<_CharT, _Traits>::__ostream_type = std::basic_ostream] operator<<(const void* __p) ^~~~~~~~ /usr/include/c++/7/ostream:245:7: note: no known conversion for argument 1 from ‘’ to ‘const void*’ In file included from /usr/include/c++/7/ostream:693:0, from /usr/include/c++/7/istream:39, from /usr/include/c++/7/sstream:38, from /usr/include/c++/7/complex:45, from /usr/include/c++/7/ccomplex:39, from /usr/include/x86_64-linux-gnu/c++/7/bits/stdc++.h:52, from Main.cc:1: /usr/include/c++/7/bits/ostream.tcc:119:5: note: candidate: std::basic_ostream<_CharT, _Traits>& std::basic_ostream<_CharT, _Traits>::operator<<(std::basic_ostream<_CharT, _Traits>::__streambuf_type*) [with _CharT = char; _Traits = std::char_traits; std::basic_ostream<_CharT, _Traits>::__streambuf_type = std::basic_streambuf] basic_ostream<_CharT, _Traits>:: ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ /usr/include/c++/7/bits/ostream.tcc:119:5: note: no known conversion for argument 1 from ‘’ to ‘std::basic_ostream::__streambuf_type* {aka std::basic_streambuf*}’ In file included from /usr/include/c++/7/regex:62:0, from /usr/include/x86_64-linux-gnu/c++/7/bits/stdc++.h:110, from Main.cc:1: /usr/include/c++/7/bits/regex.h:1525:5: note: candidate: template std::basic_ostream<_CharT, _Traits>& std::__cxx11::operator<<(std::basic_ostream<_CharT, _Traits>&, const std::__cxx11::sub_match<_Bi_iter>&) operator<<(basic_ostream<_Ch_type, _Ch_traits>& __os, ^~~~~~~~ /usr/include/c++/7/bits/regex.h:1525:5: note: template argument deduction/substitution failed: Main.cc:19:27: note: couldn't deduce template parameter ‘_Bi_iter’ cout<