Compilare: user.cpp: In function ‘int main()’: user.cpp:12:28: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i=0; i<strlen(S); i++) ^ user.cpp:14:15: warning: array subscript has type ‘char’ [-Wchar-subscripts] v[S[i]]++; ^ user.cpp:16:28: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i=0; i<strlen(S); i++) ^ user.cpp:18:18: warning: array subscript has type ‘char’ [-Wchar-subscripts] if(v[S[i]]>=2) ^