input: Write a function to calculate the sum of the digits in a given number. The function should take an integer as input and return the sum of its digits. If the input number is 0, the function should return 0.
  def sum_digits(num):
      total = 0
      while num > 0:
          digit = num % 10
          total += digit
          num = num // 10
      return total
  assert sum_digits(123)==6
  assert sum_digits(456)==15
  assert sum_digits(789)==24
  assert sum_digits(0)==0
  assert sum_digits(10101)==3
output: def sum_digits(num):
      total = 0
      while num > 0:
          digit = num % 10
          total += digit
          num = num // 10
      return total