TI-BASIC:SK:Probability

Probability functions are helpful for generating random numbers, and provide an element of variability in many calculator games. Examples would be an asteroid game where you avoid a random map of asteroids with your ship while crossing the screen, and RPGs where opponents need to have slightly unpredictable power in their attacks.

Key Commands

The main commands to use in random number generation are Rand and randInt(. By itself, rand generates a decimal number between 0 and 1. This number can be manipulated like any other number, making it very easy to set up a random event. Lets say you want to randomize the description of a character's death in an RPG. You want to say that the dragon ate him half the time, and that the dragon burnt him to a crisp the other half. This is how you could do that with rand.

:int(2rand
:If not(Ans
:Output(1,1,"The dragon ate him
:If Ans
:Output(1,1,"The dragon burned him

This works because doubling the rand command gives you a number between 0 and 2. If rand is less than .5, it will be doubled to between 0 and 1 and converted to 0 as the integer side is empty. If the number is greater than .5, it will be converted to 1 by int(. Notice that because there is only one possible outcome where the random number is a positive integer, you don't need to check if it is exactly one. We'll show you in a minute how to generate lists with rand as well.

randInt( is useful for doing the same thing as above but in a more visually simple manner. Instead of needing to convert a random decimal to integers, the calculator does the work for you. It takes either 2 or 3 arguments. The first two are the minimum and maximum, and optionally you can add a third to create a list of integers. To create a list of 20 dice rolls, the code would be like this:

:randInt(1,6,20

The same can be accomplished with rand, albeit in a more complex manner. The rand command can create lists when you add parenthesis and an argument for the size of the list.

:1+int(6rand(20

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