Transcript Session Eleven

More Repetition
While and For Loops
Sentinel-Controlled Loops
Intro to Computer Science
CS1510
Dr. Sarah Diesburg
Today’s Agenda
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Exploring looping alternatives
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For and While loops
Sentinel-Controlled vs Count-Controlled
loops
Loops
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Count-controlled loop, which means we will
know in advance how many times the loop
will run
Sentinel-controlled loop, which means we
do not know in advance how many times the
loop will run

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Controlled by sentinels
Event-controlled
3
For Loops
for varName in iterableDataStructure:
(next thing in DataStructure put in varName)
suite of code

Is a for loop count-controlled or sentinelcontrolled?
4
While Loops
while boolean expression:
statementSuite

If while loop is count-controlled, will it
contain some kind of counter?
5
Moving to Sentinel Controlled

For loops are always count-controlled

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Every for loop could be written as a while loop
(although usually a little more complicated to set
up)
While loops can behave like count controlled
loops (kid in the car from this week) but also
as sentinel-controlled loops (average quiz
score from this week).
Let’s go back to Tuesday’s Lab

The “challenge” of using a while loop is that it
is a pre-test solution.


That is, you have to have some data to work with
Several solutions to the “average” problem

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Adjusting for the extra loop (example 1)
Using a “loop and a half” (example 2)
Infinite loops with a break statement (example 3)
Let’s look at some code