combo.cpp: In function 'std::string guess_sequence(int)':
combo.cpp:27:30: warning: comparison of integer expressions of different signedness: 'int' and 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   27 |             for (int i = 0; i<N-S.size(); i++){
      |                             ~^~~~~~~~~~~
combo.cpp:32:23: warning: comparison of integer expressions of different signedness: 'int' and 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   32 |             if (coins > S.size()){
      |                 ~~~~~~^~~~~~~~~~
combo.cpp:33:34: warning: comparison of integer expressions of different signedness: 'int' and 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   33 |                 for (int i = 0; i<coins-S.size(); i++){
      |                                 ~^~~~~~~~~~~~~~~
combo.cpp:24:13: warning: unused variable 'idx' [-Wunused-variable]
   24 |         int idx = 1;
      |             ^~~