input: Write a function to create a Python class that takes a given number and calculates the sum of its digits. The class should include an initializer to store the number and a method to calculate the sum of the digits. Use the following input and output examples to verify the correctness of the function.
  
  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(1234).calculate_sum_of_digits() == 10
  assert SumOfDigits(987).calculate_sum_of_digits() == 24
  assert SumOfDigits(5).calculate_sum_of_digits() == 5
  assert SumOfDigits(0).calculate_sum_of_digits() == 0
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
  