Dice

Random(1, 6) rolls a die and gives a whole number from 1 to 6. This lesson rolls two dice, and shows why two dice are not the same as one roll from 2 to 12.

Contents

• Code
• Run
• Under the Hood
• Modify
• Make
• Good to Know

button Held -> chip roll
chip text -> decal Text

Code

@left in roll: exec
var a: int = 1
var b: int = 1
@right out text = "${a.Value} + ${b.Value} = ${a.Value + b.Value}"

on roll {
  a = Random(1, 6)
  b = Random(1, 6)
}

• Random(min, max) gives a whole number from min to max, and both ends can come up: Random(1, 6) gives 1, 2, 3, 4, 5 or 6.
• Each Random is a separate roll. a and b get two different rolls, so they can match or not.
• Random is a step, like a variable write, so it runs in a handler. The sign reads a and b from their variables.

Press the button many times. Which total comes up most often? Would Random(2, 12) give totals in the same way?

Run

1. Compile the chip and paste it in-game. Place a Button and a brick with a Text Decal.
2. Wire the Button’s Held to roll, and text to the Text Decal’s Text.
3. Press the button and watch the totals. 7 comes up most. 2 and 12 are rare.

Under the Hood

Open the chip. Each Random(1, 6) is one Random gate, with 1 typed into Min and 6 into Max. Its Exec input runs it, and it puts out a new number on Output each time. The two Random gates run one after the other in the chain, each followed by a Set Variable.

There are 36 ways two dice can land, and six of them add to 7 (1 + 6, 2 + 5, and so on), but only one adds to 2. Random(2, 12) has no such pattern. Each of its 11 totals is as likely as the others.

A Random outside a handler has nothing to run it:

@left in roll: exec
@right out face = Random(1, 6)

Error: [WS007] exec call 'Random' outside an exec context (pass exec = ... to override)

Move the roll into on roll { ... } and keep the result in a variable, as the lesson’s code does.

Modify

1. Flip a coin. Random(0, 1) gives 0 or 1. Store Random(0, 1) == 1 in a bool variable and show Heads or Tails with if heads.Value then "Heads" else "Tails", which gives the first text when heads is true and the second when it is false.

2. Count the sevens. Roll both dice into one let, and keep two counts:

   @left in roll: exec
   var rolls: int = 0
   var sevens: int = 0
   @right out text = "${sevens.Value} sevens in ${rolls.Value} rolls"
   
   on roll {
     let total = Random(1, 6) + Random(1, 6)
     rolls += 1
     if total == 7 {
       sevens += 1
     }
   }
   

   A let is one roll, however often you read it, so total is the same number in the if as on the line above. Over many rolls, about one in six is a 7.

3. Roll a twenty-sided die, Random(1, 20), and light a Point Light on a 20.

Make

Make a doubles game. Each press rolls two dice and shows them. Doubles (both dice the same) light a Point Light. Three doubles in a row light a second light, and any roll that is not a double resets the streak.

button Held -> chip roll
chip text -> decal Text
chip double -> light1 Enabled
chip streak -> light2 Enabled

Good to Know

• Random(1, 6) includes both 1 and 6. Random(0, 6) would give seven different numbers.
• Every Random call rolls again. To use one roll in two places, roll it once into a let or a variable and read that.
• Each roll is new. The dice do not remember earlier rolls, and a 6 is as likely right after a 6 as at any other time.

See Random in the reference.

Next: Random Colors.