Draw a Square

Level: Beginner · Time: 20 minutes · Chapter: 4. Motion & Coordinates

Cody's Challenge

I want to walk all the way around a square and draw it with my pen as I go. I made a start: I go forward, then I turn one corner. But when I click the green flag I stop after one side! Can you finish my program so I get all the way around and back to where I began?

What You Will Learn

• How the green flag block starts a program
• How blocks run in order, one after another, from top to bottom
• How move and turn work together to make a corner
• Why four turns of 90 degrees bring you back to facing the way you started

Before You Start

You need to know how to drag a block from the palette and snap it under another block. If you have not done that yet, work through Getting Started first.

The Starter Program

Here is how far I got. The first four blocks get me ready: they clear the stage, make my pen line thick enough to see, and put my pen down so I draw as I move. Then I go forward, pause for a second, and turn one corner.

when green flag clicked
erase all
set pen size to (5)
pen down
move (100) steps
wait (1) seconds
turn right (90) degrees

⬇ Download starter.sb3

Open it in Scratch with File → Load from your computer. You can also build these seven blocks yourself — you will remember them better if you do.

Predict Before You Run

Do not click the green flag yet. Look at my blocks and answer out loud: how many sides will I draw, and how many corners will I turn? Now click the flag and see if you were right.

Your Task

1. Find the three blocks after pen down: move, wait, and turn. Together they draw one side and turn one corner.
2. Add more blocks under the last one so that I draw a whole square.
3. Click the green flag and watch me go.

Cody's Tip

Count the corners of a square, not the sides. Every corner I turn is 90 degrees. What do you get when you add up all four corners?

Watch Out

It is easy to add all the move blocks first and then the turn blocks at the end. If you do that I walk one very long line and then spin around on the spot. Each move needs its own turn right after it.

Check Your Work

Your program is right when all four of these are true:

• There are four sides on the stage, all the same length
• The shape is closed — no gap where the last side meets the first
• I finish standing exactly where I started
• I finish facing the same direction I started, straight up

Stuck? Open this hint

Look at the group of three blocks that draws one side: move, wait, turn. A square has four sides. How many times does that group of three blocks need to appear in the program?

The Solution

Click to reveal the finished program

Try the challenge yourself first. You will remember it far longer.

when green flag clicked
erase all
set pen size to (5)
pen down
move (100) steps
wait (1) seconds
turn right (90) degrees
move (100) steps
wait (1) seconds
turn right (90) degrees
move (100) steps
wait (1) seconds
turn right (90) degrees
move (100) steps
wait (1) seconds
turn right (90) degrees

⬇ Download solution.sb3

Four sides and four corners. Each corner turns me 90 degrees, and 4 × 90 = 360 — a whole circle — which is why I end up facing exactly the way I started.

The wait 1 seconds blocks are not part of the square at all. They only slow me down so you can watch each side being drawn. Take them out and I finish in a blink.

You Did It!

You just wrote a sequence — a stack of blocks that run in order, top to bottom. That is what every program is made of, no matter how big it gets. You also found the rule that hides inside every shape I draw: the corners always add up to a full turn.

Go Further

Try these one at a time, and click the green flag after each change:

1. Change every 100 to 200. What happens to the square?
2. Delete the four wait blocks. What changes, and what stays the same?
3. Change one side's 100 to 50. What shape do you get now?
4. Change every turn from 90 to 120, and use only three sides. What shape appears? Why does that work?

Where This Goes Next

Look at how much dragging that took — twelve blocks to say the same thing four times over. Next I will show you the repeat block, which draws this exact square with three blocks instead of twelve. See Loops.

Blocks Used in This Lab

Block	Palette	What It Does
when green flag clicked	Events	Starts the script when you click the green flag
erase all	Pen	Wipes away anything drawn before
set pen size to (5)	Pen	Makes the line thick enough to see
pen down	Pen	Starts drawing a line wherever I move
move (100) steps	Motion	Moves me forward in the direction I am facing
wait (1) seconds	Control	Pauses so you can watch me draw
turn right (90) degrees	Motion	Turns me 90 degrees clockwise

Concepts Covered

From Chapter 4: Motion & Coordinates and Chapter 3: Sequencing & Scripts:

• When Green Flag Clicked
• Sequencing
• Script
• Move Steps Block
• Turn Right Block
• Degrees Of Turn