Variables

A variable is a named "box" that stores a number or text your program can read and change at any time. Created in the Variables category (red).

Create and use

Click "Make a Variable" in the Variables category, name it (say speed), and you get three blocks:

set [speed] to [50]
change [speed] by [10]
(speed)                  ← reporter block (round), drop into any input slot

Use variables instead of hard-coded numbers:

when program starts
set [followSpeed] to [35]
set movement speed (followSpeed) %

Change it in one place, every user of it updates.

The counter pattern

"change x by 1" + a loop = counting:

set [laps] to [0]
repeat until <(laps) = [3]>
  move [forward] for [2] rotations
  move [steering 100] for [340] degrees
  change [laps] by [1]
write (laps)

Variables as calibration parameters

The most valuable FLL habit: gather every number that needs field tuning at the top of the program.

when program starts
set [blackThreshold] to [30]
set [whiteThreshold] to [75]
set [followSpeed] to [30]
... everything below references these three

When venue lighting changes, you edit three numbers at the top instead of hunting through the whole program.

Lists

The Variables category can also create lists - ordered sequences of values:

add [2] to [route]
add [-1] to [route]
(item [1] of [route])
(length of [route])

Advanced idea: encode a route as a list (positive = drive rotations, negative = turn) and execute it in a loop. Most teams do fine without lists - just know the tool exists.

Show values: essential debugging

write (color sensor [C] reflected light)

Display a live sensor reading on the light matrix and read values right on the mat - threshold calibration depends on this.

Exercises

1. Create a speed variable; left hub button subtracts 10, right adds 10, and the matrix shows the value (three parallel stacks).
2. Use the counter pattern to drive a square (4x "straight + right turn 90°").

Basics complete. Next up: give the robot senses in the Sensors section.