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More Repetition While and For Loops Sentinel-Controlled Loops

More Repetition While and For Loops Sentinel-Controlled Loops. Intro to Computer Science CS1510, Section 2 Dr. Sarah Diesburg. Today’s Agenda. Exploring looping alternatives For and While loops Sentinel-Controlled vs Count-Controlled loops. Questions?. PA3?

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More Repetition While and For Loops Sentinel-Controlled Loops

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  1. More Repetition While and For Loops Sentinel-Controlled Loops Intro to Computer Science CS1510, Section 2 Dr. Sarah Diesburg

  2. Today’s Agenda • Exploring looping alternatives • For and While loops • Sentinel-Controlled vs Count-Controlled loops

  3. Questions? • PA3? • (Remember, Elise is available to help with homeworks 3-4pm M/W in WRT 339) • The lab?

  4. Loops • 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 • Controlled by sentinels • Event-controlled

  5. For Loops for varName in iterableDataStructure: (next thing in DataStructure put in varName) suite of code • Is a for loop count-controlled or sentinel-controlled?

  6. While Loops while boolean expression: statementSuite • If while loop is count-controlled, will it contain some kind of counter?

  7. Let’s go through a count-controlled example… • Annoying kid in the car (cartrip.py)

  8. For loop for counter in range(age): print("Are we there yet?")

  9. While loop counting up counter=0 while counter<age: print("Are we there yet?") #counter=counter+1 counter += 1

  10. While loop counting down while age>0: print("Are we there yet?") age -= 1 #But now age is destroyed!

  11. Moving to Sentinel Controlled • For loops are always count-controlled • 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).

  12. 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 • Adjusting for the extra loop (example 1) • Using a “loop and a half” (example 2) • Infinite loops with a break statement (example 3)

  13. Let’s look at some code

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