foo.cc: In function 'int main()':
foo.cc:18:8: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
  scanf ("%d",&a[n]);
  ~~~~~~^~~~~~~~~~~~
foo.cc:19:8: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
  scanf ("%c",&c);
  ~~~~~~^~~~~~~~~
foo.cc:22:9: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
   scanf ("%d",&a[++n]);
   ~~~~~~^~~~~~~~~~~~~~
foo.cc:23:9: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
   scanf ("%c",&c);
   ~~~~~~^~~~~~~~~

自豪的采用HydroJudge(https://github.com/hydro-dev/Hydro)进行评测。