/in/foo.cc: In function 'std::string Multi(std::string, std::string)':
/in/foo.cc:8:2: error: 'turn' was not declared in this scope
    8 |  turn(a); turn(b);
      |  ^~~~
/in/foo.cc:17:20: warning: comparison of integer expressions of different signedness: 'int' and 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   17 |  for (int i = 0; i < b.size(); i++)
      |                  ~~^~~~~~~~~~
/in/foo.cc:19:21: warning: comparison of integer expressions of different signedness: 'int' and 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   19 |   for (int j = 0; j < a.size(); j++)
      |                   ~~^~~~~~~~~~