24 CHAPTER2. WRITINGSIMPLEPROGRAMS

by: John M. Zelle

def main():
print "This programcalculates the future value of a 10-yearinvestment."

principal = input("Enterthe initial principal: ")

apr = input("Enterthe annualized interest rate: ")

for i in range(10):

principal = principal* (1 + apr)

print "The amountin 10 years is:", principal

main()

NoticethatI have addeda fewblanklinestoseparatetheInput,Processing,andOutputportionsofthe
program.Strategicallyplaced“whitespace”canhelpmake yourprogramsmorereadable.
That’s aboutit forthisexample;I leave thetestinganddebuggingasanexerciseforyou.

2.8 Exercises

1. Listanddescribeinyourownwordsthesixstepsinthesoftwaredevelopmentprocess.


2. Writeoutthechaos.pyprogram(Section1.6)andidentifythepartsoftheprogramasfollows:
   Circleeachidentifier.
   Underlineeachexpression.
   Puta commentattheendofeachlineindicatingthetypeofstatementonthatline(output,as-
   signment,input,loop,etc.)


3. A user-friendlyprogramshouldprintanintroductionthattellstheuserwhattheprogramdoes.Modify
   theconvert.pyprogram(Section2.2)toprintanintroduction.


4. Modifytheavg2.pyprogram(Section2.5.3)tofindtheaverageofthreeexamscores.


5. Modifythefutval.pyprogram(Section2.7)sothatthenumberofyearsfortheinvestmentis also
   a userinput.Make suretochangethefinalmessagetoreflectthecorrectnumberofyears.


6. Modifytheconvert.pyprogram(Section2.2)witha loopsothatit executes5 timesbeforequitting
   (i.e.,it converts5 temperaturesina row).


7. Modifytheconvert.pyprogram(Section2.2)sothatit computesandprintsa tableofCelsius
   temperaturesandtheFahrenheitequivalentsevery 10 degreesfrom0Cto100C.


8. Writea programthatconvertsfromFahrenheittoCelsius.


9. Modifythefutval.pyprogram(Section2.7)sothatit computestheactualpurchasingpowerof
   theinvestment,takinginflationintoaccount.Theyearlyrateofinflationwillbea secondinput.The
   adjustmentis givenbythisformula:

principal = principal/(1+ inflation)