input: from typing import List
  
  def diffHighestLowest(arr: List[int]) -> int:
      """ Calculate the difference between the highest and the lowest value in an array of integers.
      >>> diffHighestLowest([12, 24, 3, 8, -1])
      25
      >>> diffHighestLowest([0, -5, 10, 5, -7])
      17
      """
      lowest = min(arr)
      highest = max(arr)
      return highest - lowest
  
output:     lowest = min(arr)
      highest = max(arr)
      return highest - lowest