foo.cc: In function 'int main()':
foo.cc:23:23: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
     for (int i = 0; i < v.size() - 2; i++) {
                     ~~^~~~~~~~~~~~~~
foo.cc:31:23: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
     for (int i = 0; i < v.size() - 1; i++) {
                     ~~^~~~~~~~~~~~~~
foo.cc:42:22: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
    for (int i = 0; i < v.size() - 1; i++) {
                    ~~^~~~~~~~~~~~~~

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