combo.cpp: In function 'std::string guess_sequence(int)':
combo.cpp:17:7: warning: comparison of integer expressions of different signedness: 'int' and 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
17 | if(k==S.size()){
| ~^~~~~~~~~~
combo.cpp:20:12: warning: comparison of integer expressions of different signedness: 'int' and 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
20 | else if(k==S.size()+1){
| ~^~~~~~~~~~~~
combo.cpp:8:9: warning: control reaches end of non-void function [-Wreturn-type]
8 | string S;
| ^