7.5.STUDY INDESIGN:MAXOFTHREE 115

max = x1

x2 > max

max = x2

max = x3

x3 > max

Figure7.6:Flowchartofa sequentialapproachtothemaxofthreeproblem.

It shouldnotbesurprisingthatthelastsolutionscalestolargerproblems;weinventedthealgorithm
byexplicitlyconsideringhowtosolve a morecomplex problem.Infact,youcanseethatthecodeis very
repetitive.We caneasilywritea programthatallowstheusertofindthelargestofnnumbersbyfoldingour
algorithmintoa loop.Ratherthanhavingseparatevariablesforx1,x2,x3, etc.,wecanjustgetthevalues
oneat a timeandkeepreusinga singlevariablex. Eachtime,wecomparethenewestxagainstthecurrent
valueofmaxtoseeif it is larger.

program: maxn.py

Finds the maximumof a series of numbers

def main():
n = input("Howmany numbers are there? ")

# Set max to be thefirst value

max = input("Entera number >> ")

# Now compare the n-1 successivevalues

for i in range(n-1):

x = input("Entera number >> ")

if x > max:

max = x

print "The largestvalue is", max

main()

Thiscodeusesa decisionnestedinsideofa looptogetthejobdone.Oneachiterationoftheloop,max
containsthelargestvalueseensofar.