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.
Figure 3: A spreadsheet with order information
Here’s a program to compute the total price for the invoice. Be sure to click
to understand what’s happening here.
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csp-3-8-1: How many variables are in this program?
- 7
- Yes, quantity1, unit_price1, total1, quantity2, unit_price2, total2, invoice_total.
- 6
- There are three variables per line, two lines, and one total.
- 5
- There are three variables per line, two lines, and one total.
- 2
- There are three variables per line, two lines, and one total.
We don’t really have to create new variables quantity2 and unit_price2.
We only use those to compute the total for the line, and then we could reuse
those variable names.
(Invoice2)
- 7
- We have two fewer variables now.
- 6
- We have a total for each line (two), a quantity, a unit_price, and an invoice_total.
- 5
- The variables are quantity, unit_price, total1, total2, and invoice_total.
- 2
- We have a total for each line (two), a quantity, a unit_price, and an invoice_total.
How many variables are in this program?
Note
It is best to use variable names that make sense like invoice_total and
quantity instead of names that don’t make any sense like
this_variable_is_my_friend and fred. The name should help you
remember what the variable is representing.
Let’s say that apples are $0.40 apiece, and pears are $0.65 apiece. Modify the
program below to calculate the total cost by replacing the ?? with the
appropriate expression.
You are welcome to try out the following answers by copying and pasting them into the program above before answering this question:
-
csp-3-8-3: Which line of code will compute the correct
- total_cost = apples + pears
- That does not consider the cost of the apples or pears.
- total_cost = (0.4 * apples) + (0.65 * pears)
- 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.
- total_cost = (0.4 * pears) + (0.65 * apples)
- That gets the costs backwards
- total_cost = (0.4 + apples) * (0.65 + pears)
- That is the wrong formula for computing total cost.
total_cost if put into line
3 above?
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.
Create variables to hold each value. Calculate num_paperclips
as budget / cost_per_clip. Be sure to print the result.