input: Write a function to sort an array in ascending order using nested loops.
  assert sort_arr([3, 1, 4, 1, 5, 9, 2, 6, 5, 3, 5]) == [1, 1, 2, 3, 3, 4, 5, 5, 5, 6, 9]
  assert sort_arr([10, 9, 8, 7, 6, 5, 4, 3, 2, 1]) == [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
  assert sort_arr([]) == []
  assert sort_arr([1, 2, 3]) == [1, 2, 3]
output: def sort_arr(arr):
      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]
      return arr