View this PageEdit this PageUploads to this PageVersions of this PageHomeRecent ChangesSearchHelp Guide

lesson9-1

Work in progress. -Erik Volkman

1. What is a variable?

A variable is named thing that lets us store data for later use.
Sometimes they can be used to describe the properties of an object (length
of a car, growth speed, etc.) Often a variable has a type associated with
it, meaning that it can only hold only a specific kind of data (numbers,
words, scripts).

2. What can we do with them?

A variable can do many of the same things that a built-in property
of an object can do. We can assign values to them, change the values
stored in them, and test the value stored in a variable.

3. Activity:

Pick an object found in the classroom and come up with some quantifiable
properties of it. Use rulers, scales, your senses, and whatever else is
available to you to describe this object.
Example:
Object: Pencil
Length: 5 inches
Weight: 4 grams
Color: Red
Text on side: "Reading jogs your mind"
% Eraser Used: 50
Chewed on: Yes
Mechanical: No

Now find another similar object in the room, I would find another pencil,
and describe the object using the properties that you came up with above.
Object2: Pencil
Length: 4.5 inches
Weight: 5 grams
Color: Black
Text on side: none
% Eraser Used: 90
Chewed on: No
Mechanical: Yes

Think about this: How does changing the value of one of the properties
you described above change the object?

4. Variable Types
All variables must have a type associated with them. The type
tells what type of information can be stored in the variable. Typical
types include integers, decimal numbers, strings (words), booleans (true
or false), and colors.
Using the model for the object you created above, assign types to
each property, if you need a type that doesn't currently exist, create one
and tell us how it is different from types that already exist.

Example:
Object: Pencil
Length: decimal
Weight: decimal
Color: color
Text on side: string
% Eraser Used: integer
Chewed on: boolean
Mechanical: boolean

5. Variables in Squeak

We can create variables in Squeak too. Pull up the viewer for any
object in Squeak. Between the menu button and the name of the object there
is a down arrow, when you click on this a box will come up asking you

Link to this Page