Change Making program and the compound boolean

Dev Shed Forums Sponsor:

February 7th, 2012, 08:59 PM

bananapancakes

Registered User

Join Date: Feb 2012

Posts: 3

Time spent in forums: 45 m 4 sec
Reputation Power: 0

Change Making program and the compound boolean

I am taking an intro programming class with python and we had to write two versions of this program, one with nested branches and one simplifying it with compound boolean statements. It is supposed to make change from a dollar bill for items under a dollar, where the prices only occur in 5-cent increments. We are not allowed to use the division / operator. I wrote one with simple boolean, like this:

change= 100-price
if price <25:
print ('invalid price')
elif price >100:
print ('invalid price')
else:

if change >=75:
quarters = 3
elif change >=50:
quarters = 2
elif change >=25:
quarters = 1
else:
quarters = 0

if change-25*quarters >= 20:
dimes= 2
elif change-25*quarters >=10:
dimes = 1
else:
dimes = 0

if change-25*quarters-10*dimes >=5:
nickles = 1
else:
nickles = 0

if change != 5*nickles+10*dimes+25*quarters:
print ('invalid price')
else:
print 'your change is'
print quarters, 'quarters'
print dimes , 'dimes'
print nickles, 'nickles'

-------------------------------

I can't figure out how to make this with compound statements, can anybody see what it is that I am missing, and give me a hint about how to proceed? The only one that i can see is the starting invalid price statements at the top, I could combine those with an or statement...otherwise I feel like compound statements would just be redundant and even more cluttered...what is it that I am not seeing?

Thanks!

February 8th, 2012, 10:16 AM

b49P23TIvg

Contributing User

Join Date: Aug 2011

Posts: 1,075

Time spent in forums: 4 Weeks 1 Day 4 h 41 m 27 sec
Reputation Power: 98

Madness

Thank you for posting an effort. Good start. Some people merely post homework questions.

Using python is a good learning tool. Did you test your program or merely write it as conjecture? If I were to run your program it would fail on the first line
NameError: name 'price' is not defined

Next, indentation is an essential part of python syntax. Post python code here using code tags. Put your code into the edit window, highlight it with your mouse, and click the # icon found above the edit window. And if you have some other hardware configuration, enter
[c o d e] at the start of your program, and
[ / c o d e ] at the program end.
Remove the spaces between the square brackets.

Great, now that you've decided to actually try python, and to try harder to post python so that we don't have to guess the nesting of your if statements we'll get on with the show.

According to python documents, the compound statements are if while for try with def class

Code:

compound_stmt ::=  if_stmt
                   | while_stmt
                   | for_stmt
                   | try_stmt
                   | with_stmt
                   | funcdef
                   | classdef

The code you show contains if. Therefor, contrary to your claim, you used compound statements.

Code:

'''
    Make change using quarters, dimes, and nickels.
    No division!
    Limits: the amount of change is less than a buck and a multiple of 5 cents.

    invoke the doctests as the shell command

    $ python -m doctest -v module_name.py
'''

def change(amount,value):
    '''
        return a 2-tuple of the resulting amount and
        the number of coins used of value value.

        doctests:

        >>> change(45,25)
        (20, 1)
        >>> change(20,10)
        (0, 2)

    '''
    i = 0
    while value <= amount:
        amount -= value
        i += 1
    return (amount, i, )

A solution without compound statements:
index into a dictionary of precomputed change for keys list(range(100))[0:100:5] .

Last edited by b49P23TIvg : February 8th, 2012 at 10:33 AM.

February 9th, 2012, 11:39 PM

bananapancakes

Registered User

Join Date: Feb 2012

Posts: 3

Time spent in forums: 45 m 4 sec
Reputation Power: 0

Thank you for responding despite my failure to use the code tags, I will use them in the future, woops!

My teacher used 'simple boolean' to refer to if, else, or elif statements, and 'compound boolean' to refer to and/or statements--- I never even considered that those might not be standard terms! I don't really know how to do much beyond if/else statements right now, so your example is a bit beyond me. I have saved the code though, to see if can figure some things out from it on my own. (My class moves soooooooooo slowly.)

Thanks again for your help!

February 10th, 2012, 12:15 PM

b49P23TIvg

Contributing User

Join Date: Aug 2011

Posts: 1,075

Time spent in forums: 4 Weeks 1 Day 4 h 41 m 27 sec
Reputation Power: 98

This hideous assignment forces you to write duplicate code. Abhor duplication! You're subject to copy and paste errors. Hard to read because you have to figure out that the code does the same thing in several places. Hard to change because you have to make same changes in many places all the while remembering to rename your variables. In this version I've made the duplicate code exact to reduce the number of places to remember to change variable names. This is just awful. No loops! No user defined functions. Stupid.

Code:

import sys

print('Enter item cost [5 to 95 in multiples of 5].')
cost = int(sys.stdin.readline())
change = 100 - cost

if 95 < change:
    raise ValueError('Invalid item cost.  Too small.')
if change < 5:
    raise ValueError('Invalid item cost.  Too large.')

v = 25
coin = 0
if v <= change:
    change -= v
    coin += 1
if v <= change:
    change -= v
    coin += 1
if v <= change:
    change -= v
    coin += 1
quarters = coin

v = 10
coin = 0
if v <= change:
    change -= v
    coin += 1
if v <= change:
    change -= v
    coin += 1
dimes = coin

v = 5
coin = 0
if v <= change:
    change -= v
    coin += 1
nickels = coin

if change:
    raise ValueError('Invalid item cost.  Not a multiple of 5.')

if 100 != 25*quarters + 10*dimes + 5*nickels + cost:
    raise NotImplementedError('Incorrect program')

print('Change for $1.00:')
print('\tquarters: %d'%quarters)
print('\tdimes: %d'%dimes)
print('\tnickels: %d'%nickels)