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