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How to draw a triangle, square, pentagon or any regular shape or polygon in Scratch

Sean McManus, author of Scratch Programming in Easy Steps and Cool Scratch Projects in Easy Steps, shows you how to draw any regular shape or polygon in Scratch

One of the most enjoyable features in the Scratch programming language is the pen, which enables you to draw pictures on the screen by moving sprites around. Here's a simple program I wrote for my Code Club to show them how they can draw a triangle, square, a pentagon, septagon (or heptagon), hexagon, octogon, nonagon, decagon and on and on. I had some fun trying to remember the names for the regular shapes after an eight sided one.

How to draw polygons in Scratch

There are two important numbers you need to know:

  • The number of sides the shape has. You use this to decide how many times to repeat. To draw a square in Scratch, you repeat four times. To draw a triangle, repeat 3. Each time you repeat, you draw a line and turn a corner.
  • The angle of the turn at each corner. The way to calculate this is to take 360 and divide it by the number of sides. So to draw a square, the angle is 360/4 = 90. When drawing a triangle, it's 360/3 = 120.

My program in the next section calculates this automatically for you, but if you just want to draw a square or another shape, it's clearer to do the maths and drop the numbers in. Here's how to draw a square, for example:

when green flag clicked / clear / pen down / repeat 4 / move 100 steps / turn right 90 degrees / repeat ends

To change the length of the sides, change the number of steps the sprite moves. For shapes with more sides than 16, you'll need to use smaller side lengths, otherwise the sprite will go off the screen.

Program to draw any polygon in Scratch

When green flag clicked / ask how many sides / pen down/ repeat answer / move 50 steps / turn right 360 divided by answer degrees, end repeat

Feel free to share that program card image with your friends on Twitter, Facebook or other social network. Try it with your Code Club group, classroom or family too!

Try the program

Find out more...

Find more 10 block Scratch demos here. For more information on my Scratch books and more bonus content, visit the Scratch Programming in Easy Steps and Cool Scratch Projects in Easy Steps homepages.

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Visit www.sean.co.uk for free chapters from Sean's coding books (including Mission Python, Scratch Programming in Easy Steps and Coder Academy) and more!

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