input: Write a function to check if a given number is an Armstrong number. Return True if it is, otherwise return False. If the number is 0, return True.
  assert is_armstrong_number(153)==True
  assert is_armstrong_number(370)==True
  assert is_armstrong_number(371)==True
  assert is_armstrong_number(9474)==True
  assert is_armstrong_number(9475)==False
  assert is_armstrong_number(0)==True
output: def is_armstrong_number(num):
      if num == 0:
          return True
      digits = str(num)
      power = len(digits)
      sum_of_powers = sum(int(digit) ** power for digit in digits)
      return sum_of_powers == num