foo.cc: In function 'int num(std::string)':
foo.cc:25:18: warning: comparison of integer expressions of different signedness: 'int' and 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   25 |         while(pos<x.size()) {
      |               ~~~^~~~~~~~~

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