While Loops

1. While Loops

2. Challenge: • Ask the user a simple math questions • Continue asking the question until the user gets it right

3. A while loop actuallyrequires: • A sentry variable • An initial value for the sentry • A condition that can be triggered to end the loop • A statement inside the loop that somehow changes the sentry

4. Math Algorithm New program math game new integer correct = 5 new integer guess = 0 while (guess != correct) guess = input(“what’s 2 + 3?”) if (guess == correct){ output (“great!”) else output (“try again...”) end if end while end program

5. A while loop officially requires: • only A condition

6. A while loop actuallyrequires: • A sentry variable • An initial value for the sentry • A condition that can be triggered to end the loop • A statement inside the loop that somehow changes the sentry

7. Bad Loop new program badLoop new variable lap = 0 while lap <= 10 laps++ end while end program

8. Another Bad Loop new program badLoop new variable lap while lap != 10 lap = lap + 3 end while end program

9. Yet another bad Loop new program badLoop new variable lap = 0 while lap <= 0 lap++ end while end program

10. Challenge • Change the math program so it gives no more than three chances • Hint: still uses a while loop • Hint: count number of turns • Hint: add a special kind of sentry

11. Three Tries Algorithm New program three tries new integer correct = 5 new integer guess = 0 new integer turns = 0 new boolean keepGoing = true while (keepGoing == true) guess = input(“what’s 2 + 3?”) if (guess == correct) output (“great!”) keepGoing = false else output (“try again...”) end if turns++ if (turns >= 3){ output “too many turns” keepGoing = false end if end while end program

12. Tricks of the Three Tries Use a boolean (true/false) sentry keepGoing indicates whether loop should continue Anything that causes loop to end changes keepGoing