Programming for Children

Lessons

Primary 4 · Science and Elementary Technology

Programming for Children

5 lessons

Lesson 2 of 5

Drawing Shapes with Turtle Blocks

15 min

Let's begin

Habimana wants the turtle to draw a square. He snaps together: forward 100, right 90, forward 100, right 90, forward 100, right 90, forward 100, right 90. It works! "But that's eight blocks," says Umutoni. "I can do it with three."

How? Let's find out.

Blocks that move the turtle

forward and back move the turtle by a number of steps.
right and left turn the turtle on the spot by a number of degrees. A quarter turn is 90 degrees; a full turn is 360 degrees.
arc moves the turtle along a curve.

Blocks for the pen

pen down: the turtle draws as it moves. pen up: it moves without drawing.
set colour and set pen size change the line.
start fill and end fill colour in the shape you draw between them.

Repeat saves work

A square has 4 equal sides and 4 equal turns. So Umutoni uses the repeat block from the Flow palette:

repeat 4 [ forward 100, right 90 ]

The blocks inside the repeat run 4 times. Repeating steps like this is called a loop.

The turning rule

To draw any shape with equal sides, the turtle must turn all the way round (360 degrees) by the end. So each turn is 360 ÷ number of sides.

Shape	Sides	Turn	Program
Triangle	3	360 ÷ 3 = 120	repeat 3 [ forward 100, right 120 ]
Square	4	360 ÷ 4 = 90	repeat 4 [ forward 100, right 90 ]
Pentagon	5	360 ÷ 5 = 72	repeat 5 [ forward 80, right 72 ]
Hexagon	6	360 ÷ 6 = 60	repeat 6 [ forward 60, right 60 ]

A rectangle has two long and two short sides, so repeat 2 [ forward 150, right 90, forward 80, right 90 ].

A circle: repeat 360 [ forward 1, right 1 ], or use the arc block.

Tip

Always turn 360 in the end

Divide 360 by the number of sides and you get the turn. Triangle 120, square 90, hexagon 60.

✦

Try it yourself

Try each one first, then tap Show answer to check.

1

Write a program for a square with sides of 50 steps.

Show answerHide answer

Answer: repeat 4 [ forward 50, right 90 ]

2

Mugisha wrote repeat 3 [ forward 100, right 60 ] to draw a triangle, but the shape did not close. What is the bug?

Show answerHide answer

Answer: The turn must be 360 ÷ 3 = 120, not 60. Fix: repeat 3 [ forward 100, right 120 ].

3

An octagon has 8 sides. What is the turn?

Show answerHide answer

Answer: 360 ÷ 8 = 45 degrees.

4

How can the turtle move to a new place without leaving a line?

Show answerHide answer

Answer: Use pen up, move it, then pen down again.

Quick check

Match each shape to the turn the turtle makes at each corner.

Tap one on the left, then its partner on the right.

What you learned today

forward, back, right and left move and turn the turtle; pen blocks control the line.
repeat makes a loop, so a square is repeat 4 [ forward 100, right 90 ].
For a shape with equal sides, turn 360 ÷ number of sides.

Sources and credits

Activities/Turtle Art, by Sugar Labs wiki contributors, Sugar Labs, CC BY 4.0, adapted by Ganzaa.

The exercises (Try it yourself and the practice questions) are written by Ganzaa. Turtle Blocks is free software from Sugar Labs.

1Blocks that move the turtle

2Blocks for the pen

3Repeat saves work

4The turning rule

Try it yourself

Blocks that move the turtle

Blocks for the pen

Repeat saves work

The turning rule