input: Write a Python class that takes a given number and calculates the sum of its digits. The class should have a method named `calculate_sum_of_digits` which returns the sum of the digits of the given number.
  
  class SumOfDigits:
      
      def __init__(self, num):
          self.num = num
      
      def calculate_sum_of_digits(self):
          total = 0
          for ch in str(self.num):
              total += int(ch)
          return total
  
  assert SumOfDigits(6342).calculate_sum_of_digits() == 15
  assert SumOfDigits(12345).calculate_sum_of_digits() == 15
  assert SumOfDigits(9876).calculate_sum_of_digits() == 30
  assert SumOfDigits(0).calculate_sum_of_digits() == 0
  assert SumOfDigits(1).calculate_sum_of_digits() == 1
output: 
  class SumOfDigits:
      
      def __init__(self, num):
          self.num = num
      
      def calculate_sum_of_digits(self):
          total = 0
          for ch in str(self.num):
              total += int(ch)
          return total
  