Compilare: main.cpp: In function 'int main()': main.cpp:42:10: warning: ignoring return value of 'constexpr std::vector<bool, _Alloc>::reference std::vector<bool, _Alloc>::operator[](size_type) [with _Alloc = std::allocator<bool>; reference = std::vector<bool>::reference; size_type = long unsigned int]', declared with attribute 'nodiscard' [-Wunused-result] 42 | vis[0]; | ^ In file included from /usr/include/c++/12.2.1/vector:65, from main.cpp:3: /usr/include/c++/12.2.1/bits/stl_bvector.h:1035:7: note: declared here 1035 | operator[](size_type __n) | ^~~~~~~~