The Bike Rental Receipt

Nothing new, all at once

Every exercise so far handed you one new idea and somewhere small to try it. This one hands you no new idea at all — every line in the editor is something you've already met, arranged in the order a receipt actually gets built: values, then arithmetic on them, then the lines that print the result.

puts shows each line. Variables hold the parts that change: name, hours, rate. Arithmetic turns them into amounts: hours * rate for one row, subtotal / 10 for a tenth of the bill. An if decides whether the weekend fee applies at all. ljust and rjust are what keep the columns straight instead of drifting. An array and each print the closing notes without a separate puts for each one. And a running total collects the rental cost as it goes, exactly as it collected a week of rainfall a few exercises back.

A worked example

A laundromat ticket rather than a bike shop, so the receipt in the editor stays yours to finish:

total = 0

name = "Wash"
loads = 2
rate = 40
cost = loads * rate
total = total + cost
puts "#{name.ljust(8)}#{cost.to_s.rjust(5)}"

name = "Dry"
loads = 1
rate = 30
cost = loads * rate
total = total + cost
puts "#{name.ljust(8)}#{cost.to_s.rjust(5)}"

puts "-------------"
puts "TOTAL#{total.to_s.rjust(8)}"

Wash       80
Dry        30
-------------
TOTAL     110

Two blocks of the same six lines with different values in them, and a total nobody typed in. Change the 2 to a 3 and both the wash row and the total move with it, because both are worked out rather than written down.

Your turn

Press Run before changing anything. Most of the receipt already works correctly: the header, the first two rental rows, the weekend fee, the closing notes. Two lines are marked, and both of them already run — they're wrong, not missing.

1. The kids' bike row still prints its four values with plain spaces between them, so the numbers land nowhere near the columns above them. Rewrite it the way the two rows above it are written, with the same ljust and rjust calls and the same widths.
2. total is set to 0, so the bottom of the receipt disagrees with the rest of it. Work it out from the two values the program already has: the amount for the rentals, and the weekend fee.

If something goes wrong

The likeliest slip is the total showing 0, or a number that doesn't match the two lines above it — check that both names on the right of the = are spelled exactly as they're spelled further up the program.

If the kids' bike row prints #{name.ljust(12)} back at you word for word, an interpolation is missing its #. If it prints but sits out of line, count the widths against the two rows above rather than guessing — one number different is all it takes.