foo.cc: In function 'int main()':
foo.cc:7:16: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
    7 |         freopen("b.in","r",stdin);
      |         ~~~~~~~^~~~~~~~~~~~~~~~~~
foo.cc:8:16: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
    8 |         freopen("b.out","w",stdout);
      |         ~~~~~~~^~~~~~~~~~~~~~~~~~~~
foo.cc:16:22: warning: ignoring return value of 'int scanf(const char*, ...)' declared with attribute 'warn_unused_result' [-Wunused-result]
   16 |                 scanf("%lld",&a);
      |                 ~~~~~^~~~~~~~~~~

Found 10 testcases.