One Algorithm, Any Polygon

💡 The idea

An algorithm is a general recipe: repeat n times, go forward, turn 360 divided by n.

• The algorithm is: repeat n times, forward some distance, turn 360 divided by n.
• Star Blocks has no division sign, so you work out 360 divided by n and type the answer.
• repeat n works with a variable, so the count itself can be a value you set.
• Efficiency here means fewer commands for the same picture: one loop instead of forty lines.
• Raise n and the polygon becomes visually a circle, though it is still straight lines.

📘 Words to know

algorithm

a clear recipe of steps that solves a whole family of problems

general

works for many cases, not only one

efficiency

getting the same result with less work

👀 Watch this

A twelve-sided polygon that already looks very nearly like a circle.

# 12 sides, so the turn is 360 / 12 = 30
set n 12
set angle 30
repeat n [ forward 40 right angle ]

▶ Run it below

✍️ Your turn

1. Run it, then set n 6 and angle 60 for a hexagon.
2. Work out the pair of numbers for 9 sides and try them.
3. Set n 36 and angle 10. Count how many commands you saved.
4. Set the wrong angle on purpose and describe what the shape becomes.
5. Work out what happens to the size when you keep 40 but raise n.

🎯 Challenge: Use the same algorithm for a twenty-sided polygon. Work out the turn first, then count how many lines the same drawing would need without a loop.

# 20 sides, so the turn is 360 / 20 = 18
set n 20
set angle 18
repeat n [ forward 20 right angle ]