foo.cc: In function 'int Sort(int*, int)':
foo.cc:30:1: warning: no return statement in function returning non-void [-Wreturn-type]
 }
 ^
foo.cc: In function 'int main()':
foo.cc:50:8: error: 'a' was not declared in this scope
  cout<<a[go]<<" "<<y[go]<<endl;
        ^
foo.cc:46:18: warning: unused variable 'j' [-Wunused-variable]
  int n,i,x[100], j,y[100]; cin>>n;
                  ^

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