/in/foo.cc: In function 'bool cmp(VI&, VI&)':
/in/foo.cc:14:23: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
     for (int i = 0; i < a.size(); ++i)
                     ~~^~~~~~~~~~
/in/foo.cc: In function 'VI sub(VI&, VI&)':
/in/foo.cc:21:30: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
     for (int i = 0, t = 0; i < a.size(); ++i) {
                            ~~^~~~~~~~~~
/in/foo.cc:23:15: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
         if (i < b.size()) t -= b[i];
             ~~^~~~~~~~~~