5. Drawing Your First Shape: A Perfect Square

A square has four equal sides and four equal corners (90-degree turns). Knowing this, we can command the turtle to draw one. Here is the “long way” to do it:

fd 100

rt 90

fd 100

rt 90

fd 100

rt 90

fd 100

rt 90

Notice a pattern? You’re repeating the exact same two commands—fd 100 and rt 90—four times. In programming, repeating yourself is a sign that there’s a smarter way to work.

Logo provides a powerful shortcut called the repeat command. This is your first introduction to a core programming concept called a loop. A loop tells the computer to perform a set of actions a specific number of times.

Here is the efficient way to draw the same square:

repeat 4 [fd 100 rt 90]

Let’s break this down:

• repeat 4: This tells Logo to repeat the following instructions 4 times.
• [fd 100 rt 90]: These are the commands inside the square brackets that will be repeated.

Using repeat saves a lot of typing. More importantly, it ensures every side and every turn is exactly the same. If you typed out the commands eight times and made a single typo on line seven (rt 89 instead of rt 90), your square would be broken! A loop guarantees perfection every time.

Great job! You’ve just written a real computer program. Now let’s explore a few more useful commands to manage your creations.