/in/foo.cc: In function 'int main()':
/in/foo.cc:14:42: warning: comparison of integer expressions of different signedness: 'int' and 'const std::__cxx11::basic_string<char>::size_type' {aka 'const long unsigned int'} [-Wsign-compare]
   14 |     while ((pos = str.find(substr, pos)) != string::npos) {
      |            ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~