input: def bubble_sort(arr):
      """Sorts a given array in ascending order using the bubble sort algorithm.
      
      >>> bubble_sort([3, 7, 4, 1])
      Sorted array:
      1
      3
      4
      7
      """
output:     n = len(arr)
      for i in range(n):
          for j in range(0, n-i-1):
              if arr[j] > arr[j+1]:
                  arr[j], arr[j+1] = arr[j+1], arr[j]
      print("Sorted array:")
      for num in arr:
          print(num)