foo.cc: In function 'int main()':
foo.cc:16:23: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
     for (int i = 0; i < s.length(); i++){
                     ~~^~~~~~~~~~~~
foo.cc:45:15: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for(int i=0;i<a.size();i++)
              ~^~~~~~~~~
foo.cc: In function 'int fun(char, int)':
foo.cc:52:15: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for(int v=0;v<obj.length();v++){
              ~^~~~~~~~~~~~~

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