Compilare: user.c: In function ‘black_magic’: user.c:79:9: warning: unused variable ‘j’ [-Wunused-variable] int i, j, b[40]; int h = m + n; ^ user.c: In function ‘readfrom’: user.c:13:2: warning: ignoring return value of ‘fscanf’, declared with attribute warn_unused_result [-Wunused-result] fscanf(f, "%d %d", n, m); ^ user.c:16:4: warning: ignoring return value of ‘fscanf’, declared with attribute warn_unused_result [-Wunused-result] fscanf(f, "%d", &a[i][j]); ^