input: def diffHighestLowest(arr):
      """ Calculate the difference between the lowest and highest value for a given array of integers.
      >>> diffHighestLowest([12, 24, 3, 8, -1])
      25
      >>> diffHighestLowest([45, 10, -5, 9, 21])
      50
      """
      lowest = min(arr)
      highest = max(arr)
      return highest - lowest
output:     lowest = min(arr)
      highest = max(arr)
      return highest - lowest