Compilare: user.c: In function ‘main’: user.c:31:9: warning: array subscript has type ‘char’ [-Wchar-subscripts] if (!invalid[a][b]) { ^ user.c:31:9: warning: array subscript has type ‘char’ [-Wchar-subscripts] user.c:32:11: warning: array subscript has type ‘char’ [-Wchar-subscripts] d[j][a] += d[j ^ 1][b]; ^ user.c:32:11: warning: array subscript has type ‘char’ [-Wchar-subscripts] user.c:33:11: warning: array subscript has type ‘char’ [-Wchar-subscripts] d[j][a] -= d[j][a] / MOD * MOD; ^ user.c:33:11: warning: array subscript has type ‘char’ [-Wchar-subscripts] user.c:42:5: warning: array subscript has type ‘char’ [-Wchar-subscripts] i += d[j][a]; ^ user.c:17:9: warning: ignoring return value of ‘fscanf’, declared with attribute warn_unused_result [-Wunused-result] fscanf(f, "%d%d", &n, &m); ^ user.c:19:11: warning: ignoring return value of ‘fscanf’, declared with attribute warn_unused_result [-Wunused-result] fscanf(f, "\n%c %c", &a, &b); ^