input: Write a function to read an array from the user and then determine the mean and median of the array. The function should return both the mean and median values.
  assert mean_median([10, 15, 20, 25, 30, 35]) == (22.5, 22.5)
  assert mean_median([5, 3, 4, 1, 2]) == (3.0, 3)
  assert mean_median([1]) == (1.0, 1)
  assert mean_median([1, 2]) == (1.5, 1.5)
  assert mean_median([]) == (None, None)
output: def mean_median(arr):
      if not arr:
          return None, None
      arr.sort()
      n = len(arr)
      mean_val = sum(arr) / n
      if n % 2 == 0:
          median_val = (arr[n//2 - 1] + arr[n//2]) / 2
      else:
          median_val = arr[n//2]
      return mean_val, median_val