102 CHAPTER7. CONTROLSTRUCTURES,PART 1

Thisnewdesignhastwo simpledecisionsattheend. Theindentationindicatesthata stepshouldbe
performedonlyif theconditionlistedin thepreviouslineis met.Theideahereis thatthedecisionintroduces
analternative flow ofcontrolthroughtheprogram.Theexactsetofstepstakenbythealgorithmwilldepend
onthevalueoffahrenheit.
Figure7.1is a flowchartshowingthepossiblepathsthatcanbetakenthroughthealgorithm.Thediamond
boxesshow conditionaldecisions.If theconditionis false,controlpassesto thenext statementin thesequence
(theonebelow).If theconditionholds,however, controltransferstotheinstructionsintheboxtotheright.
Oncetheseinstructionsaredone,controlthenpassestothenextstatement.

yes

no

yes

no

fahrenheit < 30?

fahrenheit > 90?

Print a Heat Warning

Print a Cold Warning

Print Fahrenheit

Farenheit = 9/5 * celsius + 32

Input Celsius Temperature

Figure7.1:Flowchartoftemperatureconversionprogramwithwarnings.

Hereis how thenew designtranslatesintoPythoncode:

convert2.py

A program to convertCelsius temps to Fahrenheit.

This versionissues heat and cold warnings.

def main():
celsius = input("Whatis the Celsius temperature? ")
fahrenheit = 9.0 / 5.0 * celsius+ 32
print "The temperatureis", fahrenheit, "degrees fahrenheit."

# Print warningsfor extreme temps

if fahrenheit > 90:

print "It’sreally hot out there, be careful!"

if fahrenheit < 30:

print "Brrrrr.Be sure to dress warmly!"

main()

YoucanseethatthePythonifstatementis usedtoimplementthedecision.
Theformoftheifis verysimilartothepseudo-codeinthealgorithm.

if :