Chapter 9.1: Lists

• Lists are often called by another name in other programming languages – arrays.

Suppose there is a list of Customers (people waiting in line). You want to serve each

customer one at a time, so each one should walk into the store one at a time.

A. Use a DoTogether tileB. Use a DoInOrder tileC. Use a ForAllTogether tileD. Use a ForAllInOrder tile

Which of the following types can be used in a list?

A. RocketteB. Rockette’s ThighsC. Rockette’s HipsD. All of the Above

If I declare a list thusly, and use a ForAllInOrder tile, what order do the rockettes kick?

Order

A rocketterockette2rockette3

B rocketterockette3rockette2

C You can’t be sure

D None of the above

Old SuperBowl Commercialhas three frogs talk

• But what they are advertising we isn’t “ahem” a school topic – So let’s modify it.

Three Frogs

• Three frogs, together they say – Frog 1 (on left) “Hear No Evil”– Frog 2 (in middle) “See No Evil”– Frog 3 (on right) “Speak No Evil”

• That’s hard – let’s start with– Three frogs talk in order left to right– All of them say the same thing: Hello– Like this:

What does this code do?

What does this code do?A. The frogs talk in order

left to rightB. The frogs talk in

backwards order (right to left)

C. Each frog talks, but the order depends

It ALWAYS goes in the order you make your list in

Let’s assume I remake my list like

this (L to R):

What if I want the frogs to say Hello (left to right) 5 times?

A. Make a counted loop run five times INSIDE (as the inner loop) the ForAllInOrder loop

B. Make a counted loop run five times with the ForAllInOrder loop INSIDE (as the inner loop)

Predict: What would this code do?

• ???

By the way… you can make a list out of different kinds of objects

• Do the wave with different “People” objects• Make different types of flowers grow

And out of other things…

Problem: Each frog should say something different…Hear no evil

See no evil

Speak no evil

What programming construct would you use?

A. An if statement inside the For all in orderB. A counted loop inside the For all in orderC. An if statement before the For all in orderD. A counted loop outside the For all in orderE. I don’ t know…

There are (at least) two possible solutions… What is the BEST explanation of why is one

better than the other? A. Option 1 is better because it is shorterB. Option 1 is better because it does the least

number of “checks” (or boolean condition evaluations)

C. Option 2 is better because it makes clear exactly what the “checks” (or boolean condition evaluations) are

D. Option 2 is better because it has a regular structure with empty “else” portions

A) ShorterB) Least

Boolean Checks

C) Clear BooleanChecksD) RegularStructure withEmpty “else”es

Remember this…

• “Good” programs aren’t (always) the ones that– Make it easiest on the programmer– Are easiest for humans to read– Require least amount of effort from programmer

• Instead they are (usually) the ones that– Require least computing work (by computer)– Are easiest to adapt to new situations• Methods and parameters come in here

There’s an EVEN BETTER way to write this program!

• Think about this…– What if we had…• A list of froggies

– Some number of frogs that want to talk

• A list of words– Exactly the same “number” of Strings to be “said” by each of

those frogs…

– How can we make a program that will make each frog say a specific word• In ONLY 2 LINES OF CODE?!?!?

Let’s make the beetles do a more complicated dance…

• Like this:

Which structure would you want?

A. One ForAllInOrder loopB. One ForAllInOrder loop with an if statement

insideC. One if statement with a ForAllTogether insideD. None of the above

Does this code correctly implement our intended behavior?

A. YesB. NoC. I don’t know

And WHY!

What is new about this code?

• Nested “for all” loops• A loop that “iterates” over all items in a list– Inside that is another loop that goes over all the

items in a list– In this case, happen to be the same list

• Wow, you can do complicated things now…

There are 4 beetles, how many times is this instruction executed?

A. 4B. 12C. 16D. 48E. I don’t know

Parameters to methods:We can do better now!

How would we do our “new” solo (with backup)