foo.cc: In function 'int start(int, std::__cxx11::string)':
foo.cc:6:20: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for (int i = x; i < str.size(); i++)
                  ~~^~~~~~~~~~~~
foo.cc: In function 'int main()':
foo.cc:29:20: warning: 'end' may be used uninitialized in this function [-Wmaybe-uninitialized]
  for (int i = 0; i <= end; i++)
                  ~~^~~~~~

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