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Section 14.9 Figuring out an Invoice

We can use variables to solve problems like those we might solve in a spreadsheet. Imagine that you had a spreadsheet with an invoice for an office supply company.
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Figure 14.9.1. A spreadsheet with order information
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Here’s a program to compute the total price for the invoice:
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Listing 14.9.2.
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Checkpoint 14.9.3.

How many variables are in Listing 14.9.2?
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  • Yes, quantity1, unitPrice1, total1, quantity2, unitPrice2, total2, invoiceTotal.
  • There are three variables per line, two lines, and one total.
  • There are three variables per line, two lines, and one total.
  • There are three variables per line, two lines, and one total.
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We don’t really have to create new variables quantity2 and unitPrice2. We only use those to compute the total for the line, and then we could reuse those variable names.
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Listing 14.9.4.
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Checkpoint 14.9.5.

How many variables are in Listing 14.9.4
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  • We have two fewer variables now.
  • We have a total for each line (two), a quantity, a unitPrice, and an invoiceTotal.
  • The variables are quantity, unitPrice, total1, total2, and invoiceTotal.
  • We have a total for each line (two), a quantity, a unitPrice, and an invoiceTotal.
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Let’s say that apples are $0.40 apiece, and pears are $0.65 apiece. Modify the program below to calculate the total cost (it should print 3.55).
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You are welcome to try out the following answers by copying and pasting them into the program above before answering this question:
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Checkpoint 14.9.6.

Which line of code will compute the correct totalCost if put into the program above?
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  • totalCost = numApples + numPears
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  • That does not consider the cost of the apples or pears.
  • totalCost = (costPerApple * numApples) + (costPerPear * numPears)
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  • We need to multiply the cost per apple times the number of apples and add it to the cost per pear times the number of pears.
  • totalCost = (costPerApple * numPears) + (costPerPear * numApples)
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  • That gets the costs backwards
  • totalCost = (0.4 * numApples) + (0.65 + numPears)
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  • That would work, but giving names to numbers makes code easier to understand.
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Checkpoint 14.9.7.

Write the code to calculate and print how many paperclips you can buy if each paperclip is $0.05 and you have $4.00 in your pocket. It should print 80.
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Create variables to hold each value. Calculate numPaperclips as budget / costPerClip. Be sure to print the result.
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There is a hint available below. It doesn’t give the full answer, you will have to replace all of the ???’s in it with different values.
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Hint.
# 1. DECLARE VARIABLES AND ASSIGN VALUES
costPerClip = ???
budget = ???
# 2. CALCULATE RESULT
numPaperclips = ??? / ???
# 3. PRINT RESULT
print(???)
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