Lecture Notes on 05 Mar 2014

There are two different ways of using while - with a counter
and with a sentinel value.

Paradigm 1: Counter
* Initialize counter outside the loop
* Create a boolean conditional expression with the counter
  to terminate the loop
* Reset (increment or decrement) the counter in the body of
  the loop

Paradigm 2: Sentinel Value
* Read input or initialize variable that may have the sentinel value
* Create boolean conditional expression with sentinel value
* Read input within the body of the loop or reset the variable
  that may have the sentinel value

Outline of Assignment 6
def main():
  # Prompt the user to enter lower limit
  lo = int (input ('Enter starting number of the range: '))

  # Prompt the user to enter upper limit
  hi = int (input ('Enter ending number of the range: '))

  # Check validity of the input
  while ((lo < 1) or (hi < 1) or (lo > hi)):
    lo = int (input ('Enter starting number of the range: '))
    hi = int (input ('Enter ending number of the range: '))

  # Initialize variables to hold max cycle length and the corresponding number
  max_n = 0
  max_length = 0

  # Iterate over all numbers in the range
  for n in range (lo, hi + 1):
    # Initialize cycle length
    cycle_length = 0

    # Use while loop to determine cycle length for n
    ...

    # Compare cycle length with max_length outside while loop
    if (cycle_length > max_length):
      max_length = cycle_length
      max_n = n

  # Write out the result
  ...

main()

**********************************************************************

# Solution of Samuel Pepys problem

import random

def main():

  # number of trials
  num_trials = 1000

  # trial 1: 6 throws of a fair die
  trial_1 = 0
  for i in range (num_trials):
    is_one = 0
    for j in range (6):
      if (random.randint(1, 6) == 1):
        is_one += 1
    if (is_one >= 1):
      trial_1 += 1
  print ('Trial 1: ', trial_1, '/', num_trials)

  # trial 2: 12 throws of a fair die
  trial_2 = 0
  for i in range (num_trials):
    is_one = 0
    for j in range (12):
      if (random.randint(1, 6) == 1):
        is_one += 1
    if (is_one >= 2):
      trial_2 += 1
  print ('Trial 2: ', trial_2, '/', num_trials)

main()