foo.cc: In function 'int main()':
foo.cc:11:2: error: 'sort' was not declared in this scope
  sort(x+1,x+n+1);
  ^~~~
foo.cc:11:2: note: suggested alternative: 'qsort'
  sort(x+1,x+n+1);
  ^~~~
  qsort
foo.cc:8:7: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
  scanf("%d%d%d",&n,&m,&k);
  ~~~~~^~~~~~~~~~~~~~~~~~~
foo.cc:10:8: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
   scanf("%d",&x[i]);
   ~~~~~^~~~~~~~~~~~

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