Main.cc: In function ‘int _max(int, int)’: Main.cc:11:18: error: no matching function for call to ‘stoi(__gnu_cxx::__alloc_traits >::value_type&)’ if (stoi(_a[i]) > stoi(_b[j])) return a; ^ In file included from /usr/include/c++/7/string:52:0, from /usr/include/c++/7/bits/locale_classes.h:40, from /usr/include/c++/7/bits/ios_base.h:41, from /usr/include/c++/7/ios:42, from /usr/include/c++/7/ostream:38, from /usr/include/c++/7/iostream:39, from Main.cc:1: /usr/include/c++/7/bits/basic_string.h:6371:3: note: candidate: int std::__cxx11::stoi(const string&, std::size_t*, int) stoi(const string& __str, size_t* __idx = 0, int __base = 10) ^~~~ /usr/include/c++/7/bits/basic_string.h:6371:3: note: no known conversion for argument 1 from ‘__gnu_cxx::__alloc_traits >::value_type {aka char}’ to ‘const string& {aka const std::__cxx11::basic_string&}’ /usr/include/c++/7/bits/basic_string.h:6477:3: note: candidate: int std::__cxx11::stoi(const wstring&, std::size_t*, int) stoi(const wstring& __str, size_t* __idx = 0, int __base = 10) ^~~~ /usr/include/c++/7/bits/basic_string.h:6477:3: note: no known conversion for argument 1 from ‘__gnu_cxx::__alloc_traits >::value_type {aka char}’ to ‘const wstring& {aka const std::__cxx11::basic_string&}’ Main.cc:11:32: error: no matching function for call to ‘stoi(__gnu_cxx::__alloc_traits >::value_type&)’ if (stoi(_a[i]) > stoi(_b[j])) return a; ^ In file included from /usr/include/c++/7/string:52:0, from /usr/include/c++/7/bits/locale_classes.h:40, from /usr/include/c++/7/bits/ios_base.h:41, from /usr/include/c++/7/ios:42, from /usr/include/c++/7/ostream:38, from /usr/include/c++/7/iostream:39, from Main.cc:1: /usr/include/c++/7/bits/basic_string.h:6371:3: note: candidate: int std::__cxx11::stoi(const string&, std::size_t*, int) stoi(const string& __str, size_t* __idx = 0, int __base = 10) ^~~~ /usr/include/c++/7/bits/basic_string.h:6371:3: note: no known conversion for argument 1 from ‘__gnu_cxx::__alloc_traits >::value_type {aka char}’ to ‘const string& {aka const std::__cxx11::basic_string&}’ /usr/include/c++/7/bits/basic_string.h:6477:3: note: candidate: int std::__cxx11::stoi(const wstring&, std::size_t*, int) stoi(const wstring& __str, size_t* __idx = 0, int __base = 10) ^~~~ /usr/include/c++/7/bits/basic_string.h:6477:3: note: no known conversion for argument 1 from ‘__gnu_cxx::__alloc_traits >::value_type {aka char}’ to ‘const wstring& {aka const std::__cxx11::basic_string&}’ Main.cc:12:18: error: no matching function for call to ‘stoi(__gnu_cxx::__alloc_traits >::value_type&)’ if (stoi(_a[i]) < stoi(_b[j])) return b; ^ In file included from /usr/include/c++/7/string:52:0, from /usr/include/c++/7/bits/locale_classes.h:40, from /usr/include/c++/7/bits/ios_base.h:41, from /usr/include/c++/7/ios:42, from /usr/include/c++/7/ostream:38, from /usr/include/c++/7/iostream:39, from Main.cc:1: /usr/include/c++/7/bits/basic_string.h:6371:3: note: candidate: int std::__cxx11::stoi(const string&, std::size_t*, int) stoi(const string& __str, size_t* __idx = 0, int __base = 10) ^~~~ /usr/include/c++/7/bits/basic_string.h:6371:3: note: no known conversion for argument 1 from ‘__gnu_cxx::__alloc_traits >::value_type {aka char}’ to ‘const string& {aka const std::__cxx11::basic_string&}’ /usr/include/c++/7/bits/basic_string.h:6477:3: note: candidate: int std::__cxx11::stoi(const wstring&, std::size_t*, int) stoi(const wstring& __str, size_t* __idx = 0, int __base = 10) ^~~~ /usr/include/c++/7/bits/basic_string.h:6477:3: note: no known conversion for argument 1 from ‘__gnu_cxx::__alloc_traits >::value_type {aka char}’ to ‘const wstring& {aka const std::__cxx11::basic_string&}’ Main.cc:12:32: error: no matching function for call to ‘stoi(__gnu_cxx::__alloc_traits >::value_type&)’ if (stoi(_a[i]) < stoi(_b[j])) return b; ^ In file included from /usr/include/c++/7/string:52:0, from /usr/include/c++/7/bits/locale_classes.h:40, from /usr/include/c++/7/bits/ios_base.h:41, from /usr/include/c++/7/ios:42, from /usr/include/c++/7/ostream:38, from /usr/include/c++/7/iostream:39, from Main.cc:1: /usr/include/c++/7/bits/basic_string.h:6371:3: note: candidate: int std::__cxx11::stoi(const string&, std::size_t*, int) stoi(const string& __str, size_t* __idx = 0, int __base = 10) ^~~~ /usr/include/c++/7/bits/basic_string.h:6371:3: note: no known conversion for argument 1 from ‘__gnu_cxx::__alloc_traits >::value_type {aka char}’ to ‘const string& {aka const std::__cxx11::basic_string&}’ /usr/include/c++/7/bits/basic_string.h:6477:3: note: candidate: int std::__cxx11::stoi(const wstring&, std::size_t*, int) stoi(const wstring& __str, size_t* __idx = 0, int __base = 10) ^~~~ /usr/include/c++/7/bits/basic_string.h:6477:3: note: no known conversion for argument 1 from ‘__gnu_cxx::__alloc_traits >::value_type {aka char}’ to ‘const wstring& {aka const std::__cxx11::basic_string&}’