Compilare: user.c: In function ‘is_palindrom’: user.c:63:3: warning: array subscript has type ‘char’ [-Wchar-subscripts] freq[vector[i]]++; ^ user.c:70:4: warning: array subscript has type ‘char’ [-Wchar-subscripts] if(freq[vector[i]] % 2 != 0) ^ user.c:82:4: warning: array subscript has type ‘char’ [-Wchar-subscripts] if(freq[vector[i]] % 2 != 0) ^