1. More Repetition While and For loop variations
Intro to Computer Science
CS1510, Section 2
Dr. Sarah Diesburg

2. Today’s Agenda Going over yesterday’s lab
Exploring looping alternatives

3. Right and Wrong Challenge to new programmer
Isn’t there a right way to do things?
Well, there are definitely wrong ways to do things
E.g., logic errors, wrong answers, crashes
But, there are often many right ways to do something

4. Rules of Thumb
So far
Have the least amount of indents (nesting) as possible
Try to have at most two boolean expressions in a conditional statement
Use meaningful variable names

5. Loops What are the two ways we can generate repetition?
while loop and for loop
What is the purpose of a for loop?
Count-controlled loop, which means we will know in advance how many times the loop will run
Why?

6. For Loops
for varName in iterableDataStructure: (next thing in DataStructure put in varName) suite of code

7. For Loops for varName in iterableDataStructure:
(next thing in DataStructure put in varName) suite of code
varName is often called an “iterator”
Let’s take a look at quiz.py…

8. Range 3 versions range(r,s) – means range of r to s-1
range(x) – means range(0,x), which is 0 to (x-1)
range(a,b,c) – like range(a,b), but c is the “step” value
How about range(3, 10, 2)?

9. Range How many numbers are generated in range(0,8)?
How many numbers are generated in range(x,y)?

10. Range How many numbers are generated in range(0,8)?
How many numbers are generated in range(x,y)?
y-x

11. Ranges in For Loops A range is an iteratable data structure
Why was quiz.py broken?
What are all the ways quiz.py could be fixed?

12. Let’s go through an example
Annoying kid in the car (cartrip.py)

13. For loop
for counter in range(age): print("Are we there yet?")

14. While loop counting up
counter=0 while counter<age: print("Are we there yet?") #counter=counter+1 counter += 1

15. While loop counting down
while age>0: print("Are we there yet?") age -= 1 #But now age is destroyed!