/in/foo.cc: In function 'int main()':
/in/foo.cc:12:19: error: 'i' was not declared in this scope
  for(long longi=1;i<=n;i++)
                   ^
/in/foo.cc:12:11: warning: unused variable 'longi' [-Wunused-variable]
  for(long longi=1;i<=n;i++)
           ^~~~~