Compilare: user.cpp: In function ‘int main()’: user.cpp:14:26: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(i=2; i<=s.length(); ++i) ^ user.cpp:16:21: warning: array subscript has type ‘char’ [-Wchar-subscripts] if (a[s[i-1]][s[i]]) ^ user.cpp:16:27: warning: array subscript has type ‘char’ [-Wchar-subscripts] if (a[s[i-1]][s[i]]) ^ user.cpp:22:22: warning: array subscript has type ‘char’ [-Wchar-subscripts] else a[s[i-1]][s[i]]=1; ^ user.cpp:22:28: warning: array subscript has type ‘char’ [-Wchar-subscripts] else a[s[i-1]][s[i]]=1; ^