Compilare: user.cpp: In function ‘int main()’: user.cpp:18:31: warning: array subscript has type ‘char’ [-Wchar-subscripts] for(i=0;i<n;++i) ++freq[s[i]]; ^ user.cpp:22:43: warning: array subscript has type ‘char’ [-Wchar-subscripts] while(nr && st[nr]>s[i] && freq[st[nr]] && !viz[s[i]]) viz[st[nr--]]=0; ^ user.cpp:22:57: warning: array subscript has type ‘char’ [-Wchar-subscripts] while(nr && st[nr]>s[i] && freq[st[nr]] && !viz[s[i]]) viz[st[nr--]]=0; ^ user.cpp:22:72: warning: array subscript has type ‘char’ [-Wchar-subscripts] while(nr && st[nr]>s[i] && freq[st[nr]] && !viz[s[i]]) viz[st[nr--]]=0; ^ user.cpp:23:17: warning: array subscript has type ‘char’ [-Wchar-subscripts] if(!viz[s[i]]) viz[s[i]]=1,st[++nr]=s[i]; ^ user.cpp:23:28: warning: array subscript has type ‘char’ [-Wchar-subscripts] if(!viz[s[i]]) viz[s[i]]=1,st[++nr]=s[i]; ^ user.cpp:24:16: warning: array subscript has type ‘char’ [-Wchar-subscripts] --freq[s[i]]; ^