Circles and stars

If you want the turtle to draw a circle -- Think Turtle. How would a turtle walk? Try walking. Then write in your Logo program.

Look at these pictures:

The first is not at all like a circle. The second is more like a circle. The third is almost a circle.

The first is a square. We can draw it like this:

(If we want the same color as in the picture we must change it. Can you do that?) The second we can draw like this:

It gets bigger than in the picture. If you want it to be smaller the turtle should take shorter steps. The third we can draw like this:

If we repeat more times we should make smaller turns. The smaller turns we make the better the circle gets. Can you draw an even better circle? Try. At the end of the this page I will make one too.

Now let's draw a star! We only need to add one word:

Where should we add it? After FD 100. Like this:

Great! But why is it not a circle anymore? Think Turtle -- walk like the turtle would walk. Then you will understand. Remember: BK 100 means that the turtle should walk backwards 100 steps.

Let's teach the turtle a new word for star. Open the editor with "Edall". Then write:

Then click "File" and "Save and Exit". Just like before.

I promised you that I would make a better circle at the end. Here it is:

Let's teach Logo what a circle is. Open the editor with "Edall":

Click "File" and "Save and Exit". Now the turtle knows how to make a circle too!

These are the words we know now:

Logo word	What it means
FD 100	Walk forward 100 steps
BK 100	Walk backward 100 steps
LT 90	Turn left (good for drawing squares)
RT 90	Turn right (good for drawing squares)
LT 120	Turn left (good for drawing triangles)
RT 120	Turn right (good for drawing triangles)
CS	Remove everything you have drawn
HOME	Move back to the starting point (and draw a line)
PU	Lift the pen so you won't draw when you walk
PD	Put the pen towards the screen again
REPEAT 10 [       ]	Repeat what's in the box 10 times
SETPC 4	Change the pen to pen number 4
TO ... END	Remember the word after TO in the future

They are the same as on the last page. We could draw circles and stars with the words we already knew. Turtles can do much with few words.

These are the new words we have taught the turtle:

New Logo word	What it means
SQUARE	Draw a square
CIRCLE	Draw a circle
STAR	Draw a star

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