foo.cc: In function 'int main()':
foo.cc:15:20: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for (int i = 0; i < str.length(); i++)
                  ~~^~~~~~~~~~~~~~
foo.cc:17:25: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
   for (int j = 1 + i; j < str.length() + 1; j++)
                       ~~^~~~~~~~~~~~~~~~~~
foo.cc:22:20: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for (int i = 0; i < ae.size(); i++)
                  ~~^~~~~~~~~~~

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