1. Week 5 - Friday
CS 121

2. Last time
What did we talk about last time?
Repetition
while loops

3. Questions?

4. Project 2

5. Exam 1 Post Mortem

6. while Loop Examples

7. while( condition ) { statement1; statement2; … statementn; }
Anatomy of a while loop
while( condition ) {
statement1;
statement2; …
statementn; }
A whole bunch of statements

8. Guessing game
Let’s say that you wanted to write a program to guess a number that a person had come up with
The number is between 1 and 100
Every time the computer guesses a number, the person enters:
H if the number is too high
L if the number is too low
F if the number was found

9. Guessing game algorithm
Start with the minimum and maximum of the range
Find the midpoint
Ask the user if the midpoint is correct
If the answer is too high, go to Step 1 using the minimum and the midpoint - 1 as the new range
If the answer is too low, go to Step 1 using the midpoint + 1 and the maximum as the new range
If the midpoint is correct, you’re done!

10. Nested loops Just as with if-statements, it’s possible to nest loops
A repetitive task can be done inside of another repetitive task
Be careful! You can make the computer do a lot of work

11. Triangular numbers Triangular numbers are 1, 3, 6, 10, …
1 = 1
3 = 1 + 2
6 =
10 =
Let’s write a program that expresses the nth triangular number by printing 1 on the first line, 1 and 2 on the second line, 1, 2, and 3 on the third line, and so on

12. Lab 5

13. Upcoming

14. Next time…
for loops
More loop examples

15. Reminders
Keep reading Chapter 5
Keep working on Project 2