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+--- Thread: How to Think Like a Computer Scientist - Iteration Problem (/thread-4770.html)
How to Think Like a Computer Scientist - Iteration Problem - rubicana - Sep-07-2017
Please see http://interactivepython.org/runestone/static/thinkcspy/MoreAboutIteration/SentinelValuesAndValidation.html#sentinel-values
This is the code given.. (This might remove the idents - see the website if this happens)
def checkout():
total = 0
count = 0
moreItems = True
while moreItems:
price = float(input('Enter price of item (0 when done): '))
if price != 0:
count = count + 1
total = total + price
print('Subtotal: $', total)
else:
moreItems = False
average = total / count
print('Total items:', count)
print('Total $', total)
print('Average price per item: $', average)
checkout()
On the site underneath the code it states
"If you enter zero the first time you are asked for a price, the loop will end, and the program will try to divide by zero. Use an if/else statement outside the loop to avoid the division by zero and tell the user that you can’t compute an average without data."
Haven't been able to work this out - a seemingly simple if/else statement outside of the loop to catch the divide by zero. Any help gratefully received. Many thanks Tom
RE: How to Think Like a Computer Scientist - Iteration Problem - Larz60+ - Sep-07-2017
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RE: How to Think Like a Computer Scientist - Iteration Problem - rubicana - Sep-07-2017
Code from here
def checkout():
total = 0
count = 0
moreItems = True
while moreItems:
price = float(input('Enter price of item (0 when done): '))
if price != 0:
count = count + 1
total = total + price
print('Subtotal: $', total)
else:
moreItems = False
average = total / count
print('Total items:', count)
print('Total $', total)
print('Average price per item: $', average)
checkout()On the site underneath the code it states"If you enter zero the first time you are asked for a price, the loop will end, and the program will try to divide by zero. Use an if/else statement outside the loop to avoid the division by zero and tell the user that you can’t compute an average without data."
Haven't been able to work this out - a seemingly simple if/else statement outside of the loop to catch the divide by zero. Any help gratefully received. Many thanks Tom
RE: How to Think Like a Computer Scientist - Iteration Problem - ichabod801 - Sep-07-2017
That's just the code from the website. What have you tried in terms of the if/else statement, and how is it not working?
RE: How to Think Like a Computer Scientist - Iteration Problem - rubicana - Sep-07-2017
This is where I have got to. It does work to the extent of returning a message and ending the code if an initial 0 is entered. Any other initial value is ignored which isn't great (although you could argue it still works). Any help with fine tuning gratefully received.
def checkout():
total = 0
count = 0
moreItems = True
while moreItems:
price = float(input('Enter price of item (0 when done): '))
if price > 0:
count = count + 1
total = total + price
print('Subtotal: £', total)
elif price < 0:
print('Negative value - price still £',total)
else:
moreItems = False
average = total / count
print('Total items:', count)
print('Total £', total)
print('Average price per item: £', average)
price = float(input('Enter price of item (0 when done): '))
if price == 0:
print('Basket empty - Please rerun')
else:
checkout()
RE: How to Think Like a Computer Scientist - Iteration Problem - ichabod801 - Sep-07-2017
The division by zero is causing the problem. You want the if statement in checkout, right before the division, to prevent the problem from ever happening.
RE: How to Think Like a Computer Scientist - Iteration Problem - probot - Feb-03-2018
This seems to be working for me:
def checkout():
total = 0
count = 0
moreItems = True
while moreItems:
price = float(input('Enter price of item (0 when done): '))
if price > 0:
count = count + 1
total = total + price
print('Subtotal: £', total)
elif price < 0:
print('Negative value - price still £', total)
else:
moreItems = False
if total == 0:
print('Basket empty - Please rerun')
else:
average = total / count
print('Total items:', count)
print('Total £', total)
print('Average price per item: £', average)
checkout()