Hey /prog/, can you help me with something?

I'm using C++ because it's a superior language, but it's throwing this error. Can you help me?
In file included from /usr/lib/gcc/x86_64-unknown-linux-gnu/4.7.1/../../../../include/c++/4.7.1/algorithm:63:0,
                 from Ej2.cpp:3:
/usr/lib/gcc/x86_64-unknown-linux-gnu/4.7.1/../../../../include/c++/4.7.1/bits/stl_algo.h: In instantiation of 'void std::__insertion_sort(_RandomAccessIterator, _RandomAccessIterator, _Compare) [with _RandomAccessIterator = __gnu_cxx::__normal_iterator<const valla*, std::vector<valla> >; _Compare = bool (*)(const valla&, const valla&)]':
/usr/lib/gcc/x86_64-unknown-linux-gnu/4.7.1/../../../../include/c++/4.7.1/bits/stl_algo.h:2252:4:   required from 'void std::__final_insertion_sort(_RandomAccessIterator, _RandomAccessIterator, _Compare) [with _RandomAccessIterator = __gnu_cxx::__normal_iterator<const valla*, std::vector<valla> >; _Compare = bool (*)(const valla&, const valla&)]'
/usr/lib/gcc/x86_64-unknown-linux-gnu/4.7.1/../../../../include/c++/4.7.1/bits/stl_algo.h:5516:4:   required from 'void std::sort(_RAIter, _RAIter, _Compare) [with _RAIter = __gnu_cxx::__normal_iterator<const valla*, std::vector<valla> >; _Compare = bool (*)(const valla&, const valla&)]'
Ej2.cpp:54:44:   required from here
/usr/lib/gcc/x86_64-unknown-linux-gnu/4.7.1/../../../../include/c++/4.7.1/bits/stl_algo.h:2190:8: error: passing 'const valla' as 'this' argument of 'valla& valla::operator=(const valla&)' discards qualifiers [-fpermissive]
In file included from /usr/lib/gcc/x86_64-unknown-linux-gnu/4.7.1/../../../../include/c++/4.7.1/bits/stl_algo.h:63:0,
                 from /usr/lib/gcc/x86_64-unknown-linux-gnu/4.7.1/../../../../include/c++/4.7.1/algorithm:63,
                 from Ej2.cpp:3:
/usr/lib/gcc/x86_64-unknown-linux-gnu/4.7.1/../../../../include/c++/4.7.1/bits/stl_heap.h: In instantiation of 'void std::__pop_heap(_RandomAccessIterator, _RandomAccessIterator, _RandomAccessIterator, _Compare) [with _RandomAccessIterator = __gnu_cxx::__normal_iterator<const valla*, std::vector<valla> >; _Compare = bool (*)(const valla&, const valla&)]':
/usr/lib/gcc/x86_64-unknown-linux-gnu/4.7.1/../../../../include/c++/4.7.1/bits/stl_algo.h:1975:4:   required from 'void std::__heap_select(_RandomAccessIterator, _RandomAccessIterator, _RandomAccessIterator, _Compare) [with _RandomAccessIterator = __gnu_cxx::__normal_iterator<const valla*, std::vector<valla> >; _Compare = bool (*)(const valla&, const valla&)]'
/usr/lib/gcc/x86_64-unknown-linux-gnu/4.7.1/../../../../include/c++/4.7.1/bits/stl_algo.h:5365:7:   required from 'void std::partial_sort(_RAIter, _RAIter, _RAIter, _Compare) [with _RAIter = __gnu_cxx::__normal_iterator<const valla*, std::vector<valla> >; _Compare = bool (*)(const valla&, const valla&)]'
/usr/lib/gcc/x86_64-unknown-linux-gnu/4.7.1/../../../../include/c++/4.7.1/bits/stl_algo.h:2357:8:   required from 'void std::__introsort_loop(_RandomAccessIterator, _RandomAccessIterator, _Size, _Compare) [with _RandomAccessIterator = __gnu_cxx::__normal_iterator<const valla*, std::vector<valla> >; _Size = long int; _Compare = bool (*)(const valla&, const valla&)]'
/usr/lib/gcc/x86_64-unknown-linux-gnu/4.7.1/../../../../include/c++/4.7.1/bits/stl_algo.h:5514:4:   required from 'void std::sort(_RAIter, _RAIter, _Compare) [with _RAIter = __gnu_cxx::__normal_iterator<const valla*, std::vector<valla> >; _Compare = bool (*)(const valla&, const valla&)]'
Ej2.cpp:54:44:   required from here
/usr/lib/gcc/x86_64-unknown-linux-gnu/4.7.1/../../../../include/c++/4.7.1/bits/stl_heap.h:338:7: error: passing 'const valla' as 'this' argument of 'valla& valla::operator=(const valla&)' discards qualifiers [-fpermissive]
/usr/lib/gcc/x86_64-unknown-linux-gnu/4.7.1/../../../../include/c++/4.7.1/bits/stl_heap.h: In instantiation of 'void std::__adjust_heap(_RandomAccessIterator, _Distance, _Distance, _Tp, _Compare) [with _RandomAccessIterator = __gnu_cxx::__normal_iterator<const valla*, std::vector<valla> >; _Distance = long int; _Tp = valla; _Compare = bool (*)(const valla&, const valla&)]':
/usr/lib/gcc/x86_64-unknown-linux-gnu/4.7.1/../../../../include/c++/4.7.1/bits/stl_heap.h:442:4:   required from 'void std::make_heap(_RAIter, _RAIter, _Compare) [with _RAIter = __gnu_cxx::__normal_iterator<const valla*, std::vector<valla> >; _Compare = bool (*)(const valla&, const valla&)]'
/usr/lib/gcc/x86_64-unknown-linux-gnu/4.7.1/../../../../include/c++/4.7.1/bits/stl_algo.h:1972:7:   required from 'void std::__heap_select(_RandomAccessIterator, _RandomAccessIterator, _RandomAccessIterator, _Compare) [with _RandomAccessIterator = __gnu_cxx::__normal_iterator<const valla*, std::vector<valla> >; _Compare = bool (*)(const valla&, const valla&)]'
/usr/lib/gcc/x86_64-unknown-linux-gnu/4.7.1/../../../../include/c++/4.7.1/bits/stl_algo.h:5365:7:   required from 'void std::partial_sort(_RAIter, _RAIter, _RAIter, _Compare) [with _RAIter = __gnu_cxx::__normal_iterator<const valla*, std::vector<valla> >; _Compare = bool (*)(const valla&, const valla&)]'
/usr/lib/gcc/x86_64-unknown-linux-gnu/4.7.1/../../../../include/c++/4.7.1/bits/stl_algo.h:2357:8:   required from 'void std::__introsort_loop(_RandomAccessIterator, _RandomAccessIterator, _Size, _Compare) [with _RandomAccessIterator = __gnu_cxx::__normal_iterator<const valla*, std::vector<valla> >; _Size = long int; _Compare = bool (*)(const valla&, const valla&)]'
/usr/lib/gcc/x86_64-unknown-linux-gnu/4.7.1/../../../../include/c++/4.7.1/bits/stl_algo.h:5514:4:   required from 'void std::sort(_RAIter, _RAIter, _Compare) [with _RAIter = __gnu_cxx::__normal_iterator<const valla*, std::vector<valla> >; _Compare = bool (*)(const valla&, const valla&)]'
Ej2.cpp:54:44:   required from here
/usr/lib/gcc/x86_64-unknown-linux-gnu/4.7.1/../../../../include/c++/4.7.1/bits/stl_heap.h:313:4: error: passing 'const valla' as 'this' argument of 'valla& valla::operator=(const valla&)' discards qualifiers [-fpermissive]