foo.cc: In function 'int main()':
foo.cc:10:18: warning: comparison of integer expressions of different signedness: 'int' and 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   10 |  for(int i = 0;i < s.size();i++)
      |                ~~^~~~~~~~~~
foo.cc:62:8: warning: comparison of integer expressions of different signedness: 'int' and 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   62 |   if(i != s.size() - 1) //最后一个数字不用空列
      |      ~~^~~~~~~~~~~~~~~

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