Helping the Computer

Do you remember a few steps back, where I told you to write down some of your favourite values for increase and degrees, the ones that gave the best-looking patterns? If you didn’t do this, don’t worry: you can just watch the random program run for a while now and write down the combinations that give great results.

You’re going to teach Scratch those combinations of values, so it can use them to make nothing but awesome pictures!

To do this, you’ll need a list. You’ll find lists with the variables in the Variables section. Just like you did with your variables, you’ll need to create your list first!

Click Make a List, and enter Degrees List as the name.

Your list, which is empty at the moment, will appear on the Stage, and you’ll see a bunch of blocks for it in Variables.

Make another list called Increase List

Now, by clicking on the little plus sign (+) at the bottom of the lists, add in the first pair of values of increase and degrees you liked, each value into the right list. Do this again to add the second pair of values. This will be enough for now — you’ll add the rest of the value pairs you like later!

Make sure that the degrees value and the increase value that worked well together are at the same position in the Degrees List and the Increase List. They need to be there so your program can match them up again using their position!

Now you have the lists, you just need to get your code to read them and loop over them! To do this, you’re going to use a new variable to act as a counter, some incrementing, and an if then Control block.

What does incrementing mean?

To increment something means to add something to it.

You will use a variable to act as a counter to keep track of what position you’re at in your lists. To move through the lists, you’ll keep incrementing the counter by 1 (so, adding 1 to it) until you get to the end of the list.

Create a new variable called counter, and update your code to look like this:

Notice the new blocks that:

Set counter to 0, outside all the loops.
Check if the number stored in counter is the length of the list, and if so, set counter to 0. This means that this variable will always be the number of a position in the lists, and won’t get any bigger than that.
Add 1 to counter.
Pick the item from Increase List that is at the position described by counter, and put it in the increase variable. Do the same for the Degrees List and degrees variable.

How does the code work?

This is what happens when you run your program:

Set counter to 0.
Start the forever loop.
Check if counter (0) is the same as the length of Increase List (2). It isn’t.
Change counter by 1. Now counter = 1.
Set steps to 0.
Get the item at the position named by counter (1) in the Increase List, and put it in increase.
Get the item at the position named by counter (1) in the Degrees List, and put it in degrees.
Do all the stuff related to drawing the patterns.
Restart the forever loop:
Check if counter (1) is the same as the length of Increase List (2). It isn’t.
Change counter by 1. Now counter = 2.
Set steps to 0.
Get the item at the position named by counter (2) in the Increase List, and put it in increase.
Get the item at the position named by counter (2) in the Degrees List, and put it in degrees.
Do all the stuff related to drawing the patterns.
Restart the forever loop:
Check if counter (2) is the same as the length of the Increase List (2). It is!
Set counter to 0.
Continue from step 4 of this list, in a never-ending loop!

Once you’re happy with the code, go ahead and add the rest of the pairs of values you noted down to the Degrees List and the Increase List.

That’s it! Sit back and watch your program keep drawing lovely patterns in a never-ending loop! If you want to add more patterns, you can: just add more pairs of numbers to the two lists and restart the program.

Pattern Pen