Compilare: user.cpp: In function ‘int main()’: user.cpp:17:34: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i = 0; i < s.length(); ++i) ^ user.cpp:19:20: warning: array subscript has type ‘char’ [-Wchar-subscripts] v[ s[ i ] ]++; ^ user.cpp:20:23: warning: array subscript has type ‘char’ [-Wchar-subscripts] if(v[ s[ i ] ] >= 2) ^ user.cpp:16:10: warning: unused variable ‘nr’ [-Wunused-variable] int nr = 1; ^