The Henry Used Car Dealership

March 15, 2019

This is simple:

(define (henry)
  (display "Enter the sale price: ") (let ((sale (read)))
  (display "Enter the purchase price: ") (let ((purch (read)))
  (display "Profit is ") (display (- sale purch)) (newline)
  (display "Thanks for using this program.") (newline))))

> (henry)
Enter the sale price: 1100
Enter the purchase price: 800
Profit is 300
Thanks for using this program.

You can run the program at https://ideone.com/XSZrYU.

Posted by programmingpraxis

Filed in Exercises

4 Comments »

4 Responses to “The Henry Used Car Dealership”

Vincent Manis said
March 15, 2019 at 7:08 PM
HIPO charts are so 1970s. A more modern exercise would require an 11-way multiple-inheritanced class hierarchy.
matthew said
March 16, 2019 at 9:42 AM
It does seem a little old-fashioned. This book seems to be the source: https://books.google.co.uk/books?id=s72HJL9Z-4AC&pg=PT97

Globules said

March 16, 2019 at 6:04 PM

Here’s a Haskell version. Its only trick is that it will prompt repeatedly until you enter a valid amount.

import Control.Monad (msum)
import Control.Monad.IO.Class (MonadIO, liftIO)
import Control.Monad.Trans.Maybe (MaybeT(..), runMaybeT)
import Data.Decimal (Decimal)
import Data.Maybe (fromJust)
import System.IO (hFlush, stdout)
import Text.Read (readMaybe)

getProfit :: MonadIO m => MaybeT m Decimal
getProfit = do
  purchPrice <- msum $ repeat $ readValue "Enter purchase price: "
  salePrice  <- msum $ repeat $ readValue "Enter sale price: "
  return (salePrice - purchPrice)

readValue :: (MonadIO m, Read a) => String -> MaybeT m a
readValue prompt = promptRead prompt >>= maybeRead

promptRead :: MonadIO m => String -> m String
promptRead prompt = liftIO $ putStr prompt >> hFlush stdout >> getLine

maybeRead :: Monad m => Read a => String -> MaybeT m a
maybeRead = MaybeT . return  . readMaybe

main :: IO ()
main = do
  profit <- fromJust <$> runMaybeT getProfit
  print profit

$ ./usedcar
Enter purchase price: dlkjflj
Enter purchase price: 12345.67
Enter sale price: 12567.89
222.22

Daniel said

March 21, 2019 at 7:41 PM

Here’s a solution in Python.

from decimal import Decimal


def housekeeping():
    global sale_price
    sale_price = Decimal(input('sale price> '))


def detail():
    global purchase_price
    purchase_price = Decimal(input('purchase price> '))
    profit = sale_price - purchase_price
    print('profit: {}'.format(profit))


def end_of_job():
    print('Thanks for using this program')


if __name__ == '__main__':
    housekeeping()
    detail()
    end_of_job()

Example Usage:

sale price> 20.00
purchase price> 10.00
profit: 10.00
Thanks for using this program

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