Borderou de evaluare (job #569491)

Eroare de compilare: user.cpp: In function ‘int main()’: user.cpp:12:20: error: no matching function for call to ‘sqrt(std::string&)’ user.cpp:12:20: note: candidates are: /usr/include/i386-linux-gnu/bits/mathcalls.h:158:1: note: double sqrt(double) /usr/include/i386-linux-gnu/bits/mathcalls.h:158:1: note: no known conversion for argument 1 from ‘std::string {aka std::basic_string<char>}’ to ‘double’ /usr/include/c++/4.6/cmath:426:5: note: template<class _Tp> typename __gnu_cxx::__enable_if<std::__is_integer<_Tp>::__value, double>::__type std::sqrt(_Tp) /usr/include/c++/4.6/cmath:420:3: note: long double std::sqrt(long double) /usr/include/c++/4.6/cmath:420:3: note: no known conversion for argument 1 from ‘std::string {aka std::basic_string<char>}’ to ‘long double’ /usr/include/c++/4.6/cmath:416:3: note: float std::sqrt(float) /usr/include/c++/4.6/cmath:416:3: note: no known conversion for argument 1 from ‘std::string {aka std::basic_string<char>}’ to ‘float’ user.cpp:15:25: error: no match for ‘operator<’ in ‘j < a’ user.cpp:15:25: note: candidates are: /usr/include/c++/4.6/bits/stl_pair.h:207:5: note: template<class _T1, class _T2> constexpr bool std::operator<(const std::pair<_T1, _T2>&, const std::pair<_T1, _T2>&) /usr/include/c++/4.6/bits/stl_iterator.h:291:5: note: template<class _Iterator> bool std::operator<(const std::reverse_iterator<_Iterator>&, const std::reverse_iterator<_Iterator>&) /usr/include/c++/4.6/bits/stl_iterator.h:341:5: note: template<class _IteratorL, class _IteratorR> bool std::operator<(const std::reverse_iterator<_IteratorL>&, const std::reverse_iterator<_IteratorR>&) /usr/include/c++/4.6/bits/stl_iterator.h:1049:5: note: template<class _IteratorL, class _IteratorR> bool std::operator<(const std::move_iterator<_IteratorL>&, const std::move_iterator<_IteratorR>&) /usr/include/c++/4.6/bits/stl_iterator.h:1055:5: note: template<class _Iterator> bool std::operator<(const std::move_iterator<_Iterator>&, const std::move_iterator<_Iterator>&) /usr/include/c++/4.6/bits/basic_string.h:2510:5: note: template<class _CharT, class _Traits, class _Alloc> bool std::operator<(const std::basic_string<_CharT, _Traits, _Alloc>&, const std::basic_string<_CharT, _Traits, _Alloc>&) /usr/include/c++/4.6/bits/basic_string.h:2522:5: note: template<class _CharT, class _Traits, class _Alloc> bool std::operator<(const std::basic_string<_CharT, _Traits, _Alloc>&, const _CharT*) /usr/include/c++/4.6/bits/basic_string.h:2534:5: note: template<class _CharT, class _Traits, class _Alloc> bool std::operator<(const _CharT*, const std::basic_string<_CharT, _Traits, _Alloc>&) /usr/include/c++/4.6/bits/stl_iterator.h:830:5: note: template<class _Iterator, class _Container> bool __gnu_cxx::operator<(const __gnu_cxx::__normal_iterator<_Iterator, _Container>&, const __gnu_cxx::__normal_iterator<_Iterator, _Container>&) /usr/include/c++/4.6/bits/stl_iterator.h:824:5: note: template<class _IteratorL, class _IteratorR, class _Container> bool __gnu_cxx::operator<(const __gnu_cxx::__normal_iterator<_IteratorL, _Container>&, const __gnu_cxx::__normal_iterator<_IteratorR, _Container>&)