foo.cc: In function ‘bool imp(std::string)’:
foo.cc:6:26: warning: comparison of integer expressions of different signedness: ‘int’ and ‘std::__cxx11::basic_string<char>::size_type’ {aka ‘long unsigned int’} [-Wsign-compare]
    6 |         for(int j = 0; j <= s.length(); j++){
      |                        ~~^~~~~~~~~~~~~
foo.cc: In function ‘bool n16(std::string)’:
foo.cc:12:26: warning: comparison of integer expressions of different signedness: ‘int’ and ‘std::__cxx11::basic_string<char>::size_type’ {aka ‘long unsigned int’} [-Wsign-compare]
   12 |         for(int j = 0; j <= s.length(); j++){
      |                        ~~^~~~~~~~~~~~~
foo.cc: In function ‘bool n10(std::string)’:
foo.cc:18:26: warning: comparison of integer expressions of different signedness: ‘int’ and ‘std::__cxx11::basic_string<char>::size_type’ {aka ‘long unsigned int’} [-Wsign-compare]
   18 |         for(int j = 0; j <= s.length(); j++){
      |                        ~~^~~~~~~~~~~~~
foo.cc: In function ‘bool n8(std::string)’:
foo.cc:24:26: warning: comparison of integer expressions of different signedness: ‘int’ and ‘std::__cxx11::basic_string<char>::size_type’ {aka ‘long unsigned int’} [-Wsign-compare]
   24 |         for(int j = 0; j <= s.length(); j++){
      |                        ~~^~~~~~~~~~~~~