input: Write a function that calculates the sum of the digits of a given number. The function should take an integer as input and return the sum of its digits. If the number is negative, it should still calculate the sum of its digits as if it were positive.
  assert calculate_sum_of_digits(6342) == 15
  assert calculate_sum_of_digits(-6342) == 15
  assert calculate_sum_of_digits(0) == 0
  assert calculate_sum_of_digits(123456789) == 45
output: def calculate_sum_of_digits(num):
      num = abs(num)
      return sum(int(digit) for digit in str(num))