input: Write a python function to find the maximum element in an array.
  assert find_max_element([2, 7, 1, 6, 5]) == 7
  assert find_max_element([10, 20, 30, 40, 50]) == 50
  assert find_max_element([-10, -20, -30, -40, -5]) == -5
output: def find_max_element(arr):
      if not arr:
          return None
      max_element = arr[0]
      for num in arr:
          if num > max_element:
              max_element = num
      return max_element