We need to start by creating and initializing a variable to represent the number of collisions (c) that have occurred. We do this when the program starts and also turn off the main LED.

Anytime there is a collision we need to record that and we do so with the block, set c to c + 1, which increments the number of collisions each time Sphero detects one. Then we need to ask a question, is the number of collisions even or odd? We can do this using the modulo operation, represented here by the % sign in if c % 2 === 0 then. Essentially this works out to if c divided by 2 has a remainder of 0 then it is an even number, else it is an odd number. Here are some examples:

• 5 mod 2 = 1 ( 5 / 2 = 2 with a remainder of 1)
• 6 mod 2 = 0 (6 / 2 = 3 with a remainder of 0)
• 99 mod 2 = 1 (99 / 2 = 49 with a remainder of 1)
• 100 mod 2 = 0 (100 / 2 = 50 with remainder of 0)
• 123458932 mod 2 = 0 (123458932 / 2 = 61729466 with remainder of 0)

If the result of c % 2 === 0 is TRUE then we set the main LED to a random color, else we turn it off. c % 2 === 0 is a boolean operation that results to either TRUE or FALSE.

Block Types: Events, Variables, Lights, Control, Operator, Comparators

You'll notice that this example uses another variable (c_even) of type boolean, that holds the value of whether the number of collisions is even or odd.

This example has a slightly different outcome. Can you figure out why? Is the different outcome the intended one for the task given? What does the outcome tell us about our algorithm?

Block Types: Events, Variables, Lights, Control, Operator, Comparators