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

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

3. Some Things From PA02 BMI These were continuous regions.
Set up your code to handle all areas…

4. Some Things From PA02
BMI
While this is valid mathematically, it is bad form in programming languages.
And it causes real problems when not set up properly.

5. Some Things From PA02
BMI
Recognize that these are four related categories. This makes it much easier to use if/elif/else.

6. Some Things From PA02
BMI
Recognize that these are four related categories. This makes it much easier to use if/elif/else.

7. Some Things From PA02
BMI
Recognize that these are four related categories. This makes it much easier to use if/elif/else.

8. 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

9. 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?

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

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 Thursday’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