#
#  Compare two implementations of a function that count how many
#  times a particular value occurs within a list.
#

#
#  Count the number of times that a particular value appears in a list.
#
#  Parameters:
#    data: The list of values to evaluate
#    what: The value that we are looking for
#
#  Return: The number of times what occurs in data
#
def count_for(data, what):
  count = 0
  for item in data:
    if item == what:
      count = count + 1
  return count

#
#  Count the number of times that a particular value appears in a list.
#
#  Parameters:
#    data: The list of values to evaluate
#    what: The value that we are looking for
#
#  Return: The number of times what occurs in data
#
def count_while(data, what):
  count = 0
  while len(data) > 0:
    item = data.pop()
    if item == what:
      count = count + 1
  return count

#
#  Demonstrate that changes made inside count_while also impact the
#  list in the main program.
#
def main():
  test_values = [1, 2, 3, 4, 5, 4, 3, 2, 3, 4, 2, 1, 1, 1, 2, 3]

  print("Using count_for, 1 occurrs in test_values", count_for(test_values, 1), "times")
  print("Now test_values is", test_values)

  print("Using count_while, 1 occurrs in test_values", count_while(test_values, 1), "times")
  print("Now test_values is", test_values)

  print("Using count_for, 1 occurrs in test_values", count_for(test_values, 1), "times")
  print("Now test_values is", test_values)

main()