Compilare: user.cpp: In function ‘int main()’: user.cpp:38:31: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i = 0; i < s.size(); ++i) ^ user.cpp:59:52: warning: array subscript has type ‘char’ [-Wchar-subscripts] while( op.empty() == 0 && prop[ s[ i ] ] <= prop[ op.top() ] ) ^ user.cpp:59:72: warning: array subscript has type ‘char’ [-Wchar-subscripts] while( op.empty() == 0 && prop[ s[ i ] ] <= prop[ op.top() ] ) ^