combo.cpp: In function 'std::string guess_sequence(int)':
combo.cpp:15:27: warning: comparison of integer expressions of different signedness: 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} and 'int' [-Wsign-compare]
15 | for(int x; r.length() < N - 1; ){
| ~~~~~~~~~~~^~~~~~~
combo.cpp:18:14: warning: comparison of integer expressions of different signedness: 'int' and 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
18 | if(x == r.length() + 1){
| ~~^~~~~~~~~~~~~~~~~
combo.cpp:20:18: warning: comparison of integer expressions of different signedness: 'int' and 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
20 | if(x == r.length()){ r += a[0]; r += a[2]; }
| ~~^~~~~~~~~~~~~
combo.cpp:21:18: warning: comparison of integer expressions of different signedness: 'int' and 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
21 | if(x == r.length() + 1){ r += a[1]; r += a[2]; }
| ~~^~~~~~~~~~~~~~~~~
combo.cpp:22:18: warning: comparison of integer expressions of different signedness: 'int' and 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
22 | if(x == r.length() + 2){ r += a[1]; r += a[1]; }
| ~~^~~~~~~~~~~~~~~~~
combo.cpp:26:18: warning: comparison of integer expressions of different signedness: 'int' and 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
26 | if(x == r.length()){ r += a[1]; r += a[0]; }
| ~~^~~~~~~~~~~~~
combo.cpp:27:18: warning: comparison of integer expressions of different signedness: 'int' and 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
27 | if(x == r.length() + 1){ r += a[0]; r += a[1]; }
| ~~^~~~~~~~~~~~~~~~~
combo.cpp:28:18: warning: comparison of integer expressions of different signedness: 'int' and 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
28 | if(x == r.length() + 2){ r += a[0]; r += a[0]; }
| ~~^~~~~~~~~~~~~~~~~
combo.cpp:31:19: warning: comparison of integer expressions of different signedness: 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} and 'int' [-Wsign-compare]
31 | if(r.length() < N){
| ~~~~~~~~~~~^~~