Compilare: user.cpp: In function ‘int main()’: user.cpp:18:12: warning: array subscript has type ‘char’ [-Wchar-subscripts] v[a][b]=1; ^ user.cpp:18:15: warning: array subscript has type ‘char’ [-Wchar-subscripts] v[a][b]=1; ^ user.cpp:19:12: warning: array subscript has type ‘char’ [-Wchar-subscripts] v[b][a]=1; ^ user.cpp:19:15: warning: array subscript has type ‘char’ [-Wchar-subscripts] v[b][a]=1; ^