foo.cc: In function 'int main()':
foo.cc:9:10: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
     scanf("%d",&n);
     ~~~~~^~~~~~~~~
foo.cc:10:27: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
     for(i=0;i<n;i++) scanf("%d",&a[i]);
                      ~~~~~^~~~~~~~~~~~

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