1. Chapter 3: Variables, Functions, Math, and Strings
Starting Out with Alice: A Visual Introduction to Programming
Third Edition
by Tony Gaddis

2. 3.1
Variables
Programs may need to store data when running and it stores that data in a variable
A variable is a named storage location in the computer’s memory
The following types of data (or variables) can be stored:
local variables
parameter variables
class-level variables
world-level variables

3. Variable Types Local variables Parameter variables
3.1
Variable Types
Local variables
belongs to a specific method
used only by the instructions that the variable belongs to
when a method stops, the variables cease to exist
Parameter variables
used to hold an argument that is passed to a called method
Class-level variables
variable that belongs to a specific object
World-level variables
variable that belongs to the world

4. Creating Local Variables
3.1
Creating Local Variables
Local variables belong to a specific method (such as world.my first method)
Variables require 3 things:
name
type
initial value
name
type
value

5. Names and Types and Initial Values
3.1
Names and Types and Initial Values
Variable Names
Must be unique within the method
Should be meaningful and reflect the variable’s purpose
Named using camelCase
Variable Types
Numbers, Boolean, Objects, Other (such as String, Color, or Sound)
Initial Value
Value initially stored in the variable

6. Variables Tile appearance shows the type of variable
3.1
Variables
Tile appearance shows the type of variable
Creating the tile is called variable declaration
variable area

7. Variable Assignment Variables have an initial value
3.1
Variable Assignment
Variables have an initial value
Initial value held until a different value is assigned
New values can be assigned while the method is running
Set instructions can be created to store (or set) different values
Request to set a value occurs when variable tile dropped into Methods Editor

8. Variable Task……

9. Functions Each object has a set of primitive functions
3.2
Functions
Each object has a set of primitive functions
List of functions is categorized
Boolean logic
Math
Random
String
Ask user
Mouse
Time
Advanced math
Other

10. Asking the User for Input
3.2
Asking the User for Input
World has three primitive functions that ask for user input
Each function is displayed in a dialog box
Is it Yes or is it No?

11. Primitive Object Functions
3.2
Primitive Object Functions
Each object has primitive functions different from the world’s primitive functions
Proximity
Size
Spatial relation
Point of view
Other

12. Task….
-Complete Tutorial 3-1 Creating and using a variable on page
-Complete tutorial 3-2 Creating a set instruction for a variable on pages
Create the tutorial 3-3 on page 122 which is called Calling an ask user function on pages (You will use Tutorial 3-2 the jumping penguins for this task)

13. Creating Math Expressions
3.3
Creating Math Expressions
Math Operators are used to create math expressions
Math expressions perform a calculation and return a value
Operands appear to the right and left of an operand payRate * hoursWorked
“payRate” and “hoursWorked” are operands
Operator
Description +
Addition -
Subtraction *
Multiplication /
Division

14. Task……..
Create tutorial 3-4 called Using a proximity function on pages
Complete the Using Math to avoid collisions within Tutorial 3-5 on pages

15. Working with Strings and Text
3.4
Working with Strings and Text
A string is a sequence of characters
Strings represent:
names
addresses
messages
etc.

16. Asking the User to Enter a String
3.4
Asking the User to Enter a String
World’s primitive function can ask use to enter string (text)
The function returns the text the user enters
Joining separate sets of strings is called concatenation
“Hello” joins with the user’s name
What’s your name?
Hello, Jo!

17. Joining Strings String Concatenation
3.4
Joining Strings
String Concatenation
Joins string a with string b
Strings a and b are arguments
Does not change the values of strings a or b…but combines the two strings
Strings are NOT just text… but any alphanumeric character
Can convert numbers to a string for use as well

18. Task….
Open Tutorial 3-5 and add the Nerd and the methods that are located on page Remember to first create a variable called name, then drag the variable into the method to assign an initial value, then you will use the worlds function to ask user for a string and finally use the Nerds method to say what was typed. Then add a way to join strings(figure3-49)
Complete the tutorial on page called Converting a Number variable to a string.

19. Text can be added to Alice worlds
3.4
3D Text
Text can be added to Alice worlds
3D text option is available at the end of the local gallery

20. Skills Check……
Students will choose two of the following to complete from pages 146 – 148. (50 points each)
-Exercise 1,3,4,5
Students should complete the following challenge programs(100 points each)
7&8