input: Write a function to calculate the average of a list of positive integers and print the result. The function should take a list of positive integers as input and return the average as a float. If the input list is empty, the function should return 0.0.
  assert calculate_average([1, 5, 6, 7, 8]) == 5.4
  assert calculate_average([10, 20, 30, 40]) == 25.0
  assert calculate_average([]) == 0.0
  assert calculate_average([1]) == 1.0
  assert calculate_average([5, 10, 15, 20, 25, 30]) == 17.5
output: def calculate_average(numbers):
      if not numbers:
          return 0.0
      return sum(numbers) / len(numbers)