The snake is always moving in one direction, and we need to remember which direction that is.

An easy way to do that is by assigning a number to each direction. Because we’re sane human beings, let’s come up with a scheme that’s easy to remember. Let’s use a compass as a reference, and assign 0 to North, 1 to East, 2 to South, and 3 to West.

We can then create constants to make working with direction easier. Add them to our CON block from before.

Now we gotta track that number in a variable. There are only four directions, so byte-sized is plenty large. Let’s add a variable called snakedir to our VAR block from before.

Now here comes a big change. In the last exercise, we directly controlled the snake with LameControl:

We’re going to change that code a lot. We will control only the direction with LameControl, and then have the movement code look at snakedir only to decide how the snake should move.

I know it looks like a lot of code, but it’s the same logic repeated 4 times, one for each direction. Just try not to make a typo.

The first thing you’ll notice is that now the dot seems to have a mind of its own! This is because we programmed it to move if it has a direction, and it always does.

All in all, the snake is looking pretty good…​ for a single dot. There’s one more thing we need to add to really move like a snake. You’ll notice that if you are moving in one direction, you can go in the exact opposite direction, which the snake shouldn’t be able to do.

We’ll add code to prevent that.

This code lets you go up/down if you’re heading left/right, and vice versa, but you can’t do U-turns. It’s a small change, but this a big part of what makes Snake difficult.

One final change. Since there is more room horizontally than vertically, we’ll make life slightly easier by changing the starting direction to right. This will give the player more time to react before hitting a wall.