1. Iteration with While
You can say that again

2. Problem
You want to add 100 numbers

3. Problem
100 variables?
int a,b,c,d…. cin >> a; cin >> b; … int answer = a + b + c…

4. Problem Use one variable 100 times?
int num, answer = 0; cin >> num; answer += num; cin >> num; answer += num; …

5. Golden Rule of Programming
If you write the same code more than once you are probably doing it wrong.

6. Problem Repeat to eliminate duplication: int num, answer = 0;
Repeat 100 times cin >> num; answer += num;

7. While While statement expression Boolean expression
statement is the body of the loop
Usually compound using { }
After executing, test expression again

8. While Sample Sample loop Counts 1 to 100 Happens once Happens 0+ times

9. While Sample Sample loop Expression : boolean expression
True – execute body, then check again
False – done; skip to end of loop

10. Infinite Loop Condition is always true : infinite loop
Ctrl-C breaks a program

11. While Sample Sample loop Expression : boolean expression
Usually tests a variable (loop control variable)

12. Loop Control Variables
i, j, k : accepted identifiers for loop control variables

13. While Sample Sample loop Update: change loop control variable
"Go to next step"
Do as first or last thing in loop body

14. Infinite Loop No update to LCV = infinite loop
int i = 0; while(i < 20) { cout << i << " "; //i never changes!!! }

15. Counting Example
Start at 10, count by 5's, count until 50

16. Making a list
Formatting numbers as a list: version 1

17. Making a list
Formatting numbers as a list: version 2

18. Few Problems are Unique
Pattern solving is pattern recognition

19. Patterns of Loop Use Typical use patterns Total some values
Average some values

20. Total Total something up: Declare variable before
Add current value in loop
Use total after

21. Average Find average Get total Get count
Use counting variable
After loop, divide total by count

22. Average
Find average - correct