Compilare: user.c: In function ‘multi’: user.c:12:11: warning: operation on ‘a’ may be undefined [-Wsequence-point] a = (a <<= 1)%MOD; ^ user.c: In function ‘main’: user.c:32:17: warning: unused variable ‘C’ [-Wunused-variable] long long A, B, C; ^ user.c:34:8: warning: ignoring return value of ‘freopen’, declared with attribute warn_unused_result [-Wunused-result] freopen("classictask.in", "r", stdin); ^ user.c:35:8: warning: ignoring return value of ‘freopen’, declared with attribute warn_unused_result [-Wunused-result] freopen("classictask.out", "w", stdout); ^ user.c:37:6: warning: ignoring return value of ‘scanf’, declared with attribute warn_unused_result [-Wunused-result] scanf("%lld %lld %lld", &A, &B, &MOD); ^