foo.cc: In function 'bool judge(std::__cxx11::string)':
foo.cc:75:14: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
 for(int i=0;i<s.size();i++)
             ~^~~~~~~~~
foo.cc: In function 'std::__cxx11::string div(std::__cxx11::string, std::__cxx11::string, int)':
foo.cc:72:1: warning: control reaches end of non-void function [-Wreturn-type]
 }
 ^

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