foo.cc: In function 'int main()':
foo.cc:26:2: error: 'prinf' was not declared in this scope
  prinf("%d",&ans);
  ^~~~~
foo.cc:26:2: note: suggested alternative: 'printf'
  prinf("%d",&ans);
  ^~~~~
  printf
foo.cc:21:7: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
  scanf("%d",&n);
  ~~~~~^~~~~~~~~
foo.cc:23:8: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
   scanf("%d",&b[i]);
   ~~~~~^~~~~~~~~~~~

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