input: Write a python function to find the maximum and minimum values in a list of numbers.
  assert get_max_min([1, 2, 3, 4, 5, 6, 7, 8, 9, 10])==(10, 1)
  assert get_max_min([10, 20, 45, 67, 84, 93])==(93, 10)
  assert get_max_min([5, 7, 9, 8, 6, 4, 3])==(9, 3)
output: def get_max_min(numbers):
      if not numbers:
          return None, None
      max_val = numbers[0]
      min_val = numbers[0]
      for num in numbers[1:]:
          if num > max_val:
              max_val = num
          if num < min_val:
              min_val = num
      return max_val, min_val