Programming with Alice
Computing Institute for K-12 Teachers
Summer 2011 Workshop
Session 7
Pre-Project

Design an Alice program that not only determines the
mean of a collection of numbers supplied by the user
stored in an array, but also finds the median and range.
What is a List?

A list is very similar to an array. It contains multiple
variables of the same type.

Arrays have a definite size which must be set before the
program starts. Lists are different and allow the
programmer to add elements to the list dynamically. This
means a list can grow in size while the program is running.

Say we wanted to ask the user for as many numbers as
they want to enter. With an array, eventually we would run
out of space. However, a list grows as the user adds data.
This gives us a little more flexibility when programming.
Lists

Go ahead and make a list by creating a new variable.
Change “array” to “list” and check the box to the left of list
(the same way we did to create an array).

Now that we have a list created, drag it to your method to
display the list’s methods. The below menu will be
displayed. Keep the menu up so we can follow along:
Insert Methods for Lists

This is an “insert at beginning of
list” method which can add items to the beginning of the
list. The first box represents the number to be inserted into
the list and the second box shows which list will be
affected.

The “insert at end of list” method is
similar to the previous method except it inserts an item at
the end of the list. The boxes are exactly the same.

This is an “insert at position”
method which allows the list to act similar to an array. Like
arrays, lists in Alice index their elements. This block allows
us to insert something anywhere we want in the list
depending on the index value. The first box represents the
number being inserted, the second represents the position
(index) at which we want to insert the item, the 3rd box is
the same as before.
Remove Methods for Lists

This is a “remove item from
beginning of list” which removes the first item from the
list; the second item then becomes the first.

This is a “remove item from end
of list” method. It does exactly what it says.

This is a “remove item from
position” method which, for example, removes item from
index 2. Item 3 becomes item 2, item 4 becomes item 3,
etc.

This is a “remove all items from list”
method which allows the user to clear the list.
Dynamic Size of Lists

The following example will show the dynamic capability of
a list’s size. We will use a loop to take input from the user.

Drag a while loop to your method, place an “ask user for
yes or no” function in the conditional part of the while loop.

Now enter something such as “Would you like to add a
number to the list?”
Dynamic Size of Lists

We want to insert an item at the beginning of the list. To
do this, drag the list inside the while loop and choose the
appropriate method.

Place an “ask user for a number” function inside the
number part of the previously placed method. The default
question will work fine.

This loop will allow the programmer to prompt the user to
enter as much input as desired and store the input into a
list.
Step Through a List

Now let’s use a loop to step through the list. To test this we
will make the camera say each number.

Drag a loop under the while loop and select anything for
now.

Drag the list into the number area of the loop to replace
what was previously chosen.

This will bring up the list’s functions. Select the “size of
list” function (refer to slide notes for more details).
Step Through a List cont.

Now drag a camera “say” method into the loop. Place a
“what as a string” function (world object) as the string
parameter in the say method. Select anything for now.

Drag the list and place it into the function “what as a
string.” From this menu, mouse-over the “ith item from
list” function, mouse-over expressions and choose index.
Let’s test!
For All In Order Loop

Alice has conveniently created a loop specifically designed
to step through a list. The “for all in order” loop does
exactly that.

Delete the current for loop and everything it contains.

Drag a “for all in order loop” and place it where your
previous loop was located. Mouse-over expressions and
choose your list.
For All In Order Loop

Place a “camera say” method inside our “for all in order
loop,” mouse-over expressions and select “item_from_list.”

Test your program. Notice it steps through the list exactly
as the previous loop did. Either loops will work in a
situation like this.
For All Together Loop

A “for all together” loop is similar to a “do together”
container. Like the “for all in order” loop, a list is needed. If
we use this loop with our previous example, it would print
all the words in the list to the screen at the same time.
This seems useless when used like this but if we wanted
multiple object to do something at the same time, we could
put them into a list and use this loop.

To better understand this, let’s do a small example. Create
a new project and add 5 bird objects. We plan to make all
5 birds fly away at the same time.
For All Together Loop

We could use a “do together” container and place the “fly
away” methods of the bird objects inside it but using a “for
all together” loop may be easier.

Create a new list of type object and name it “birds.” This
list will hold our birds we previously created.

Create new items for the list and assign the birds
previously created to the items of the list (remember, the
list must be of type object for us to hold objects in it).
For All Together Loop

Now place a “for all together” loop in your program,
mouse-over expressions and choose your list.

Drag one of the bird objects’ “fly away” method and place
it in the “for all together” loop (not the fly method, the fly
away method), mouse-over expressions, mouse-over
item_from_birds, and select 0.25. (the number is a
parameter for this method signifying how fast to make the
bird fly away)
For All Together Loop

Let’s test this project. Notice all birds fly away at the same
time. Discussed earlier was a way of doing the same thing
with a “do together” container. Think about how this might
be accomplished.
Project 7

Design an Alice program that not only determines the
mean of a collection of numbers supplied by the user, but
also finds the median and range. This time, use lists
instead of arrays. If you have completed the project, feel
free to have the program find the mode as well.
Day 4 Questions

What three types of Boolean logical functions do we cover?

Boolean logic deals with true or false values.
( true/__false)

Where are Boolean expressions most commonly used?

Can two blocks run at the same time? If so, how could this
be accomplished?

What is the difference between an array and a list in Alice?

If you wanted to store 20 numbers supplied by the user,
should an array or list be used?

Is it possible to rearrange(sort) items in a list?

In the following array, find and write down the value with
an index of 3. [2, 41, 16, 7, 10]
Answer Key

What three types of Boolean logical functions do we cover? And, or,
not

Boolean logic deals with true or false values.( X true/__false)

Where are Boolean expressions most commonly used? conditional
branches/ while loops

Can two blocks run at the same time? If so, how could this be
accomplished? Yes, through the use of a “do together” block

What is the difference between an array and a list in Alice? Array
cannot change size and is faster, a list is dynamic and is slightly
slower

If you wanted to store 20 numbers supplied by the user, should an
array or list be used? since the size is known ahead of time an array
should be used

Is it possible to rearrange(sort) items in a list? Yes

In the following array, find and write down the value with an index of
3. [2, 41, 16, 7, 10] 7