INQ241B
Mobile Apps

Random

• math->random
• generates random numbers between zero and the upper bound exclusive
• so x := math→random(100) will be between 0 and 99 (inclusive)
• turtle→forward(x)
• non-deterministic programs, turtle will move different distance forward each time

Conditionals

• allow for branching in the execution of the program
• essentially if this then do this otherwise do this
• easiest to show this with an example

• create turtle script

  var x := 1
  turtle.forward(100)
  if x = 1 then
      turtle.left(60)
  else
      turtle.right(60)
  end
  turtle.forward(100)

• note that there are two equal operators, one is := for creating variables, the other = tests for equality
• can change the value of x, rerun and get different behavior
• but this is not very interesting if we know what the value of x will be

• need to add randomness and put in a loop

Probability

• can use random numbers, conditionals, and loops to create probability that something will happen

• for example,

  for 0 <= i < 100
      var x := math→random(10)
      turtle.forward(10)
      if x = 0 then
          turtle→set pen color(colors→random)
      else do nothing end

• the turtle has a 1 in 10 (or 10%) chance of changing color

• what if wanted it to change more frequently, or less frequently?

Turtle State

• Can get the position of the turtle with the functions turtle→xcor and turtle→ycor
• Can get the dimensions of the window with turtle→world width and turtle→world height
• These are useful when you want to write conditionals about the turtle’s position in the window… like you will in todays activity

Quiz

• m.socrative.com
• Room name ‘INQ241’

Activity

• Activity 5