/in/foo.cc: In function 'int main()':
/in/foo.cc:12:10: warning: unused variable 'arr' [-Wunused-variable]
     int *arr=(int *)malloc(sizeof(int)*1000000);
          ^~~
/in/foo.cc:16:7: warning: unused variable 'arr' [-Wunused-variable]
  int *arr = (int *)malloc(sizeof(int)*100);
       ^~~
/in/foo.cc:20:8: error: 'arr' was not declared in this scope
   cin>>arr[i];
        ^~~
/in/foo.cc:21:7: error: 'arr' was not declared in this scope
  sort(arr,arr+n);
       ^~~
/in/foo.cc:21:16: error: 'sort' was not declared in this scope
  sort(arr,arr+n);
                ^