/in/foo.cc: In function 'int main()':
/in/foo.cc:15:21: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
   for (int j = 0; j < a.size(); j++)
                   ~~^~~~~~~~~~
/in/foo.cc:26:16: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
    if ((j + 1) == a.size())
        ~~~~~~~~^~~~~~~~~~~