input: Write a python function to determine if a number is even or odd and print "even" or "odd" respectively. If the input is not an integer, print "x must be an integer".
  assert even_odd(4) == "even"
  assert even_odd(7) == "odd"
  assert even_odd("string") == "x must be an integer"
output: def even_odd(x):
      if not isinstance(x, int):
          return "x must be an integer"
      elif x % 2 == 0:
          return "even"
      else:
          return "odd"