Exact Instructions

Try telling a friend to make a jam sandwich using only short steps. If you say 'put jam on bread', they might put the jar on top of the loaf. You meant open the jar, spread jam on a slice, but you left that out. A computer has the same problem: it does not fill in gaps.

Good steps are small and unambiguous. 'Forward' means move one square. 'Turn left' means rotate without moving. Each step should do one thing. If you need two things, write two steps.

Open the robot lab beside this lesson and run the Straight line plan. Three forwards, no turns. The robot reaches the flag because every step meant one move.

Run the Find the bug plan in the lab. The robot walks into a wall on the last forward. Nothing is wrong with the robot. Step four told it to move when there was no space.

Debugging is the word for finding that wrong step. You read the plan from the start and ask: after each step, where should the robot be? The first step that does not match reality is the bug.

Try the Turn first plan too. Sometimes you need a turn before a forward. If you only write forwards, the robot never faces the flag.

The robot grid is a toy version of what programs do. Later you will write commands in a language, but the idea stays: a list of instructions, run in order, with no guessing.

Good coders still draw plans on paper before they type. The plan can be boxes and arrows, or a numbered list like the robot lab. The paper version is cheaper to fix than code.

Before you leave this topic, write five steps for brushing your teeth so someone who has never seen a toothbrush could follow them. Count how many details you almost skipped.