1. Nate Brunelle Today: Repetition, Repetition
CS1110
Nate Brunelle
Today: Repetition,
Repetition

2. Questions?

3. Last Time
While loops
For loops

4. “While” Loops while loop
Keep repeating until the boolean expression is False
“so long as this is True, keep doing the action”
Guard Condition
while boolean expression:
action1
action2
Body/ Inside

5. Rules for While Loops
Some aspect of the Guard Condition must change in the body
It must change in a way such that it will eventually become false
Note: The guard is checked at the end

6. “for” Loops For loop for [variable v] in [collection]: action
Do the action a certain number of times
“do the action once per each thing in here”
The variable takes the value of each thing in the collection in order
for [variable v] in [collection]:
action
for i in range(5):
print(‘hi’)
Range(5) -> [0,1,2,3,4]

7. Collections Order doesn’t matter, No Repetition
Order Matters, Repetition ok
Examples:
String
List
Tuple
Range
Counting starts at 0
collection[index] gives a specific value in the collection
Order doesn’t matter, No Repetition
Examples:
Set
Dict

8. Range range(x) range(x,y)
Gives all integers from 0 (inclusive) to x (exclusive)
range(5) -> 0,1,2,3,4
range(x,y)
Gives all integers from x (inclusive) to y (exclusive)
Range (2, 6) -> 2,3,4,5
[lower, upper)

9. hello Strings Collection of characters Order Matters Repetition ok
X = “hello”
X[0] -> h
hello 1 2 3 4
Indices

10. Which kind of loop? I know condition to stop repeating
I know the number of times I want to repeat
I want to repeat once per thing in a collection