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Lesson 5 · The Polygon Function

Module 1 · Learning to Drive

Lesson 5 · The Polygon Function

50–60 minPhase A · Blockly FoundationSynthesis challenge
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This is the big one. You'll combine everything from Lessons 2–4 — loops, functions, parameters, and the angle formula — into a single function that draws any regular polygon. Tell it how many sides and how long, and it figures out the rest.

Learning Objectives

By the end of this lesson you will be able to:

  • Combine a loop, a function, and parameters to solve one bigger problem
  • Compute the turn angle inside the function with 360 ÷ sides
  • Test one function against many shapes (triangle, square, hexagon, octagon…)
  • Explain how one general function replaces a whole pile of specific ones
Printable knowledge checks — the 3 questions from this lesson on one page, with room to write. Teachers: answer key.

One function to draw them all​

So far each shape needed its own function. But look at the pattern: every polygon is repeat N times: drive a side, turn 360 ÷ N. The only things that change are the number of sides and the side length — perfect for parameters. And the angle? The function can calculate it itself.

A polygon function with parameters sides and side_length: a Repeat sides times containing Straight cm side_length and Turn Deg 360 ÷ sides
One function draws every regular polygon. The two parameters are sides and side_length; the turn angle is computed from sides.

The new trick is putting a math division block (360 ÷ sides) right into the Turn block's angle slot. Now sides does double duty: it sets how many times the loop repeats and it sets the angle.

Notice what is not a parameter: Effort stays at 0.5 in both blocks. A parameter earns its place when callers actually need to vary it — sides and side_length change with every shape, speed doesn't.

Activity · Test it like an engineer​

Real programmers test one function against many inputs. In your main program, call polygon with different values and predict each shape before it runs:

Wait for button press
call polygon (sides: 4, side_length: 30)
call polygon (sides: 3, side_length: 30)
call polygon (sides: 6, side_length: 20)
call polygon (sides: 8, side_length: 15)

Write down what you expect each line to draw before you upload. Then run it and see whether the robot agrees with you.

Knowledge Check

What turn angle will polygon compute for a 12-sided shape (a dodecagon)?

Knowledge Check

polygon (8, 25) traces an octagon about 2 m around. What does polygon (8, 50) do?

Activity · Explore​

  1. Run the four test shapes above and check each one roughly closes back to its start.
  2. Notice what happens as sides go up (10, 12, 20): the shape gets closer and closer to a circle.
  3. Challenge: draw a pentagon, Turn 72°, then draw the pentagon again — the two overlapping pentagons make a star/mandala.
Knowledge Check

Without a general polygon function, you'd write one function each for square, triangle, pentagon, hexagon, and octagon. With polygon, how many functions do you need?

Real-world connections​

Writing one flexible tool instead of many rigid ones is the heart of good engineering:

Software

Libraries

A charting library draws any chart from parameters — you don't write new code for every graph.

Design

Parametric CAD

Engineers define a part once with parameters, then generate every size from the same model.

Manufacturing

Configurable machines

One programmable machine makes many products by changing inputs, not by rebuilding the machine.

Wrap-up​

  • What two parameters does polygon take, and what does each control?
  • How does the function get the turn angle? (360 ÷ sides, computed inside.)
  • Why is one general function better than many specific ones? (Less code, fewer bugs, easier to change.)

Resources​