Compilare: user.cpp: In function ‘int main()’: user.cpp:17:31: warning: array subscript has type ‘char’ [-Wchar-subscripts] for(i=0;i<n;++i) ++freq[s[i]]; ^ user.cpp:20:15: warning: array subscript has type ‘char’ [-Wchar-subscripts] if(freq[s[i]]==1) cout<<s[i]; ^ user.cpp:21:20: warning: array subscript has type ‘char’ [-Wchar-subscripts] else if(freq[s[i]]) ^ user.cpp:24:33: warning: array subscript has type ‘char’ [-Wchar-subscripts] while(j<n && !freq[s[j]]) ++j; ^ user.cpp:25:44: warning: array subscript has type ‘char’ [-Wchar-subscripts] if(s[i]<s[j]) cout<<s[i],freq[s[i]]=0; ^