/in/foo.cc: In function 'int main()':
/in/foo.cc:19:23: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
     for (int j = 0; j < _ins.size(); ++j) {
                     ~~^~~~~~~~~~~~~
/in/foo.cc:20:31: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
         for (int i = j + 1; i < _ins.size(); ++i) {
                             ~~^~~~~~~~~~~~~
/in/foo.cc:26:30: warning: format '%d' expects argument of type 'int', but argument 2 has type 'std::set<int>::size_type {aka long unsigned int}' [-Wformat=]
     printf("%d", _ins2.size());
                              ^