MrW's Computing Blog

You may copy and paste code from these instructions to save time typing.

Start a new LOGO file
Type:
    reset
    setpensize 5

Copy the following PROCEDURE:

    to snowflake
    repeat 6 [fd 20 bk 20 rt 60]
    end

Now whenever you want to draw a snowflake, you just have to write snowflake  rather than typing all of the code for a snowflake.  The code above is called a PREOCEDURE – it teaches the computer a new word and what it means.

Try this

    snowflake
    repeat 10 [snowflake fd 20 rt 36]

Why did we use the numbers 10 (for repeat) and 36 (for the right turn)?

You can also add a VARIABLE to a procedure.  Change the snowflake procedure to this:

    to snowflake :size
    repeat 6 [fd :size bk :size rt 60]
    end

Now when you call snowflake, you need to put a number with it, which will be how big it is.

Try this:

snowflake 50

snowflake 100

You can add other variables to the snowflake too.  Change the procedure to this:

to snowflake :size :col :pensize
   colour :col
   setpensize :pensize    
   repeat 6 [fd :size bk :size rt 60]
end

Then type for example:   snowflake 60 “blue 10

Let’s make a snowstorm…

Copy this code:

repeat 100
[
pu setxy (250 – random 500) (250 – random 500) pd
snowflake random 50 “blue random 15
]

Now tinker, play, experiment…

You could add this after the reset: colour “blue fill then make your snowflakes white

1. j2launch – 
2. Click on Level 3 
3. Type reset
4. This code draws a single step like the one below:
   • fd 30
   • rt 90
   • fd 30
   • lt 90
5. Press play – you should get this: 
6. Now add this to your code:
   • pu
     setxy -200 50
     pd
7. Challenge 1:  Make this shape by typing more instructions: 
8. Now add this to your code:
   • pu
     setxy 130 100
     pd
9. Challenge 2: Now make a square:  
10. Now add this to your code:
    • pu
      setxy -140 -140
      pd
11. Challenge 3:  
12. Now add this to your code:
    • pu
      setxy 140 – 140
      pd
13. Challenge 4: 

The final picture should look like this:

Is there any way we could make our code simpler?  Some of the algorithms repeat instructions.

Success steps:

• Copy instructions carefully
• Press play to run program
• Make instructions to draw simple shapes including forward, left and right
• Check instructions carefully for mistakes (bugs)

If you have finished, try working through these debugging challenges!

And if you finish that…!  Start a new file and start with this code.

• reset
• setpensize 5

Can you draw a letter?  ~(Diagonal letters will need rt 45 or lt 45)