Variables and Expressions

Narrated by Horst

draw_tree(225, 35)
draw_tree(420, 45)
draw_house(720, 60)
draw_snow_person(300, 20)

• How to use variables (this chapter)

• How to write expressions (this chapter)

• How to create our own functions (the next two chapters)

How to Use Variables

Variable and Function Names

Good Variable Names

• temperature_in_celsius

• tree_position_1

• tree_position_2

• car_speed

• number_of_children

• simpson

Bad Names, that still work:

• temperatueInCelsius - Uses capital letters. Keep it lower case and use underscores.

• x - Too short, and not descriptive.

• Smith - Starts with a capital letter.

Names that don't work:

• tree position - Can’t use spaces

• 4runner - Can’t start with a number

Constants

• Variables that don't change are constants

• They should be in all upper-case

• PI = 3.14159

• SCREEN_WIDTH = 800

How to Create Expressions

Using Operators in Expressions

What's Different?

• Juxtaposition doesn't work - It doesn't multiply
• The '=' isn't an algebraic equality - It is an assignment

Juxtaposition Doesn't Work

Assignment Operators

Increasing a Variable

Increment/Decrement Operators

Using Expressions In Function Calls

Order of Operations

average = 90 + 86 + 71 + 100 + 98 / 5

average = (90 + 86 + 71 + 100 + 98) / 5

Printing Variables

Review