input: Write a python function to classify integers as 'negative', 'zero', or 'positive'.
  assert classify_int(-5) == 'negative'
  assert classify_int(0) == 'zero'
  assert classify_int(10) == 'positive'
output: def classify_int(n):
      if n < 0:
          return 'negative'
      elif n == 0:
          return 'zero'
      else:
          return 'positive'