input: Write a function to determine if a given number is an Armstrong number. If the number is an Armstrong number return True else return False. If the number is negative then return False.
  assert is_armstrong_number(153)==True
  assert is_armstrong_number(371)==True
  assert is_armstrong_number(9474)==True
  assert is_armstrong_number(1234)==False
  assert is_armstrong_number(-54748)==False
  assert is_armstrong_number(0)==True
output: def is_armstrong_number(num):
      if num < 0:
          return False
      digits = str(num)
      n = len(digits)
      sum_of_powers = sum(int(digit) ** n for digit in digits)
      return sum_of_powers == num