Question about snake game

[aliensoldier]

Here's a port of an n6 example game. Hopefully you can find some clues by looking at the code   I don't remember why I implemented the game like this, and probably there are smarter ways.

Code:

' Port of n6 example game.

SNAKE_MAX_LENGTH = 30*40
UP = 1
DOWN = 2
LEFT = 3
RIGHT = 4
snake = dim(SNAKE_MAX_LENGTH, 2)
level = dim(40, 30)

set window "Smape", 320, 240, false, 2
set redraw off

do
    snakeLength = 1
    snakeHead = 0
    snakeDirection = 0
    speed = 10
    speedCounter = speed
    snake[snakeHead][0] = 20
    snake[snakeHead][1] = 15
    for y = 0 to 29  for x = 0 to 39  level[x][y] = 0
    gameOver = false
    nextPlupTime = clock()
    do
        if clock() >= nextPlupTime
            if rnd(3) = 0  level[rnd(40)][rnd(30)] = 2
            else  level[rnd(40)][rnd(30)] = 1
            nextPlupTime = clock() + 2000 + rnd(2000)
        endif

        if keydown(38) and snakeDirection <> DOWN  snakeDirection = UP
        if keydown(40) and snakeDirection <> UP  snakeDirection = DOWN
        if keydown(37) and snakeDirection <> RIGHT  snakeDirection = LEFT
        if keydown(39) and snakeDirection <> LEFT  snakeDirection = RIGHT
   
        speedCounter = speedCounter - 1
        if speedCounter = 0
            prev = snakeHead
            if snakeDirection > 0  snakeHead = (snakeHead + 1)%SNAKE_MAX_LENGTH
            speedCounter = speed
            if snakeDirection = UP
                snake[snakeHead][0] = snake[prev][0]
                snake[snakeHead][1] = snake[prev][1] - 1
            elseif snakeDirection = DOWN
                snake[snakeHead][0] = snake[prev][0]
                snake[snakeHead][1] = snake[prev][1] + 1
            elseif snakeDirection = LEFT
                snake[snakeHead][0] = snake[prev][0] - 1
                snake[snakeHead][1] = snake[prev][1]
            elseif snakeDirection = RIGHT
                snake[snakeHead][0] = snake[prev][0] + 1
                snake[snakeHead][1] = snake[prev][1]
            endif
            x = snake[snakeHead][0]
            y = snake[snakeHead][1]
            if x < 0 or x >= 40 or y < 0 or y >= 30
                gameOver = true
            else
                if level[x][y] > 0
                    snakeLength = snakeLength + 1
                    if level[x][y] = 2  speed = max(speed - 1, 0)
                    level[x][y] = 0
                endif
            endif
        endif

        set color 0, 0, 0
        cls

        for y = 0 to 29
            for x = 0 to 39
                if level[x][y] = 1
                    set color 0, 255, 0
                    draw rect x*8, y*8, 8, 8 , true
                elseif level[x][y] = 2
                    set color 255, 0, 0
                    draw rect x*8, y*8, 8, 8, true
                endif
            next
        next

        set color 255, 255, 255
        set caret 0, 0
        x = snake[snakeHead][0]
        y = snake[snakeHead][1]
        for i = snakeHead to snakeHead - snakeLength + 1
            j = i
            if j < 0 then j = j + SNAKE_MAX_LENGTH
            draw rect snake[j][0]*8, snake[j][1]*8, 8, 8, true
            if i <> snakeHead
                if snake[j][0] = x and snake[j][1] = y then gameOver = true
            endif
        next

        wait 10
        redraw
    until gameOver
loop

I'll see if I can understand the code where the body follows the head, thank you.