foo.cc: In function 'bool part(std::string&, std::string&)':
foo.cc:27:18: warning: comparison of integer expressions of different signedness: 'int' and 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   27 |         while (j < b.size() && ++i < a.size())
      |                ~~^~~~~~~~~~
foo.cc:27:36: warning: comparison of integer expressions of different signedness: 'int' and 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   27 |         while (j < b.size() && ++i < a.size())
      |                                ~~~~^~~~~~~~~~
foo.cc:28:28: warning: comparison of integer expressions of different signedness: 'int' and 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   28 |                 while (++j < b.size() && b[j] != a[i]);
      |                        ~~~~^~~~~~~~~~
foo.cc:29:18: warning: comparison of integer expressions of different signedness: 'int' and 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   29 |         return j <= b.size();
      |                ~~^~~~~~~~~~~

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