Compilare: main.cpp: In function 'int main()': main.cpp:10:19: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int i=0;i<s.size();i++) ~^~~~~~~~~ main.cpp:12:21: warning: array subscript has type 'char' [-Wchar-subscripts] if (viz[s[i]]) ^ main.cpp:17:22: warning: array subscript has type 'char' [-Wchar-subscripts] else viz[s[i]]=1; ^