input: Write a function that prints out the Pascal's triangle for a given number of rows. The function should return None.
  assert pascal_triangle(5)==None
output: def pascal_triangle(n):
      for line in range(1, n + 1):
          C = 1
          for i in range(1, line + 1):
              print(C, end=" ")
              C = C * (line - i) // i
          print()