Core Concepts (25 min)

Let’s learn the basic building blocks that all programming uses.

Variables: Things That Can Change¶

Variables store information that can change over time.¶

Examples in real life:

• Your age (changes every year)

• Your bank account balance (goes up and down)

• Your location (changes as you move)

Examples in NetLogo:

• age - how old is this turtle?

• wealth - how much money does this turtle have?

• xcor - what is the turtle’s x-coordinate?

• color - what color is this turtle?

Think of Variables as Labels¶

Imagine each turtle wearing name tags:

Commands: Actions Agents Can Take¶

Commands tell agents what to do.

Basic movement commands¶

• forward 1 - move forward 1 step

• right 90 - turn right 90 degrees

• left 45 - turn left 45 degrees

Property change commands¶

• set color red - change color to red

• set size 2 - make turtle bigger

• die - remove this turtle from the world

Social commands:¶

• create-link-with turtle 5 - form connection with turtle #5

• ask neighbors - give instructions to nearby turtles

Reporters: Questions Agents Can Answer¶

Reporters ask questions and get answers.¶

About myself:

• who - what is my ID number?

• xcor - what is my x-coordinate?

• count my-links - how many connections do I have?

About others:

• count turtles - how many turtles exist?

• count neighbors - how many turtles are near me?

• mean [wealth] of turtles - what’s the average wealth?

About the environment:

• pcolor - what color is the patch I’m on?

• patches in-radius 3 - which patches are within 3 units?

Procedures: Grouping Instructions Together¶

Procedures are like recipes - they group related instructions.

to move-randomly
  right random 360    ; turn a random amount
  forward 1           ; move forward 1 step  
end

This procedure called move-randomly does two things:

1. Turn a random direction (0-360 degrees)

2. Move forward 1 step

Now you can just say move-randomly instead of repeating those two lines!

Why use procedures?¶

• Organize related instructions

• Avoid repeating the same code

• Make code easier to read and understand

• Break complex tasks into smaller pieces