Eroare de compilare: user.cpp: In function ‘void Sort()’: user.cpp:30:23: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (i=1; i < V.size();++i) ^ user.cpp: In function ‘void ConvexHull()’: user.cpp:42:29: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int i = 2; i < V.size(); ++i) ^ In file included from /usr/local/include/c++/4.8.0/algorithm:62:0, from user.cpp:2: /usr/local/include/c++/4.8.0/bits/stl_algo.h: In instantiation of ‘_RandomAccessIterator std::__unguarded_partition(_RandomAccessIterator, _RandomAccessIterator, const _Tp&, _Compare) [with _RandomAccessIterator = __gnu_cxx::__normal_iterator<std::pair<double, double>*, std::vector<std::pair<double, double> > >; _Tp = std::pair<double, double>; _Compare = bool (*)(std::pair<double, double>&, std::pair<double, double>&)]’: /usr/local/include/c++/4.8.0/bits/stl_algo.h:2319:78: required from ‘_RandomAccessIterator std::__unguarded_partition_pivot(_RandomAccessIterator, _RandomAccessIterator, _Compare) [with _RandomAccessIterator = __gnu_cxx::__normal_iterator<std::pair<double, double>*, std::vector<std::pair<double, double> > >; _Compare = bool (*)(std::pair<double, double>&, std::pair<double, double>&)]’ /usr/local/include/c++/4.8.0/bits/stl_algo.h:2360:62: required from ‘void std::__introsort_loop(_RandomAccessIterator, _RandomAccessIterator, _Size, _Compare) [with _RandomAccessIterator = __gnu_cxx::__normal_iterator<std::pair<double, double>*, std::vector<std::pair<double, double> > >; _Size = int; _Compare = bool (*)(std::pair<double, double>&, std::pair<double, double>&)]’ /usr/local/include/c++/4.8.0/bits/stl_algo.h:5513:44: required from ‘void std::sort(_RAIter, _RAIter, _Compare) [with _RAIter = __gnu_cxx::__normal_iterator<std::pair<double, double>*, std::vector<std::pair<double, double> > >; _Compare = bool (*)(std::pair<double, double>&, std::pair<double, double>&)]’ user.cpp:33:34: required from here /usr/local/include/c++/4.8.0/bits/stl_algo.h:2287:35: error: invalid initialization of reference of type ‘std::pair<double, double>&’ from expression of type ‘const std::pair<double, double>’ while (__comp(*__first, __pivot)) ^ /usr/local/include/c++/4.8.0/bits/stl_algo.h:2290:34: error: invalid initialization of reference of type ‘std::pair<double, double>&’ from expression of type ‘const std::pair<double, double>’ while (__comp(__pivot, *__last)) ^