Fall 2007 ACS-1805 Ron McFadyen 1

Ch 9 Lists

• In some animations, several objects must perform the same actions

• Example:

• A marching band, where the band members are performing the same marching steps.

• In such situations, it is convenient to collect all the objects into a list – a group or collection of objects

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Lists

• With Alice, we can organize objects into a list.

• In our daily lives, we use lists to help us organize things. For example,

• to-do list

• assignments

• shopping

• In programming, a list is a special kind of data structure.

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Types of Lists• In Alice, a list can be a list of numbers or a list of objects, colors, or other

type ….

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Example

• The famous Rockettes® are preparing for their winter holiday show. You have been hired to create an animation for the holiday show that will be used on a web site where people can purchase tickets for the show.

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Creating the list

Create the initial world and add five rockette objects to the world.

Then, create a new world-level variable in the properties panel.

(Why should it be world-level?)

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Creating the listIn the popup dialog box,

type in a name

select Object type

check “make a List” box

click new item button 5 times to select each of the 5 rockettes, one at a time

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Programming with lists

• One of the most useful operations with a list is to repeatedly perform some action with each item in the list.

This is called iteration or "iterating through a list."

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Iterating through a list

• Two control structures for iterating through a list:

• in order (one at a time)• all together (simultaneously)

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Example: Iteration in Order

• A typical chorus line dance involves each dancer (one after the other) kicking up a leg.

• Possible storyboard:

For all dancers in order item_from_dancers kickUpRightLeg

kickUpRightLeg

Parameter: whichRockette

Do in order Do together whichRockette right thigh turn back whichRockette right calf turn forward whichRockette right calf turn back

• Implementing in Alice ….

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Example: Iteration all together

• A typical chorus line dance involves each dancer (one after the other) kicking up a leg.

• Possible storyboard:

For all dancers simultaneously item_from_dancers kickUpRightLeg

kickUpRightLeg

Parameter: whichRockette

Do in order Do together whichRockette right thigh turn back whichRockette right calf turn forward whichRockette right calf turn back

• Implementing in Alice ….

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Common Uses of Lists

• Iterating through a list of several like items to accomplish the same task with each item.

• As in the previous Rockettes example

• Iterating through a list of several like items to search for an item with a given property...

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Example

• A WacAMole arcade game.

• Little moles pop up from holes in the top of the booth. The user tries to whack the mole before it drops out of sight.

• The game is over when 10 moles are whacked.

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Designing the game

• To design the game animation, we need to answer several questions:

• How will the game work, overall?

• How do we keep score?

• How do we know when the user whacks a

mole?

• How will a list help us?

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How will the game work?

• A mole pops up and then goes back down. Each time the mole pops up, the user attempts to use the mouse to click the mole.

• When a click occurs, we check to see if a mole was clicked. If so, a sound plays and the score increases.

• The above actions repeat until the game is over.

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Is the game over?

Overall design

pop random mole

no

yescongratulate

Mouse click event

See next slide

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Overall design

Did mouse click on a mole?

yes Play sound

Change score display

Mouse click event

no

do nothing

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Storyboard for overall game

• This is the main driver for the game.

• The code will be written in World.my first method

While the game isn't over randomly select one mole and call popMole

Congratulate the user

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Storyboard: popMole

popMole

Do in order Move the mole up Wait some time Move the mole back down

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Keeping Score

• We will use a visual scorekeeper.

• The scorekeeper is made up of two cylinders• A gray cylinder above the

ground • A yellow cylinder below the

ground.• Each cylinder is 1 meter in height.

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Keeping score

• Each time the user successfully clicks a mole, the yellow cylinder will move up 1/10 meter.

• When the yellow cylinder is above ground (has moved up 10 times), the game is over.

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When a mole is clicked

• This is where a list comes in handy:

• create a list of the moles (one mole is below each hole)

• create a mouse click event

• each time the mouse is clicked, call a score method to iterate through the list of moles to see whether one of the moles has been clicked!

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Storyboard: keep score

Event: User clicks mouseResponse: score

For All in order If any mole in the mole list was the object clicked

Make a noise Move the playerscore (yellow cylinder) up 1/10 meter

And implementing in Alice …