/in/foo.cc: In function 'int main()':
/in/foo.cc:17:16: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for (i = 0; i < ivec.size(); i += 2)
              ~~^~~~~~~~~~~~~
/in/foo.cc:23:31: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
   for (j = (i % 2 ? 0 : 1); j < ivec.size(); j += 2)
                             ~~^~~~~~~~~~~~~
/in/foo.cc:27:15: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
    else if (j == ivec.size() - 1) { left = ivec.size() - 2; right = 0; }
             ~~^~~~~~~~~~~~~~~~~~
/in/foo.cc:34:31: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
   for (j = (i % 2 ? 1 : 0); j < ivec.size(); j += 2)
                             ~~^~~~~~~~~~~~~
/in/foo.cc:40:16: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for (k = 0; k < ivec.size(); ++k)
              ~~^~~~~~~~~~~~~