Compilare: main.cpp: In function 'int main()': main.cpp:35:29: warning: comparison of integer expressions of different signedness: 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} and 'int' [-Wsign-compare] 35 | if (left_brackets.find(c) != -1) | ~~~~~~~~~~~~~~~~~~~~~~^~~~~ main.cpp:56:28: warning: comparison of integer expressions of different signedness: 'std::stack<char>::size_type' {aka 'long unsigned int'} and '__gnu_cxx::__alloc_traits<std::allocator<int>, int>::value_type' {aka 'int'} [-Wsign-compare] 56 | if (brackets.size() == stack_sizes.back()) | ~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~ main.cpp:83:28: warning: comparison of integer expressions of different signedness: 'std::stack<char>::size_type' {aka 'long unsigned int'} and '__gnu_cxx::__alloc_traits<std::allocator<int>, int>::value_type' {aka 'int'} [-Wsign-compare] 83 | if (brackets.size() == stack_sizes.back()) | ~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~ main.cpp:111:28: warning: comparison of integer expressions of different signedness: 'std::stack<char>::size_type' {aka 'long unsigned int'} and '__gnu_cxx::__alloc_traits<std::allocator<int>, int>::value_type' {aka 'int'} [-Wsign-compare] 111 | if (brackets.size() == stack_sizes.back()) | ~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~