input: 
  def diffHighestLowest(arr):
      """
      Calculates the difference between the highest and lowest values in a given array of integers.
      >>> diffHighestLowest([12, 24, 3, 8, -1])
      25
      >>> diffHighestLowest([1, 1, 1, 1])
      0
      """
      lowest = min(arr)
      highest = max(arr)
      return highest - lowest
  
output:     lowest = min(arr)
      highest = max(arr)
      return highest - lowest