(Another) Snake Game - Getting The Snake To Collide With Itself

[Kaykao]

What is it you are trying to achieve?
I'm making (yet another) version of snake.


What is the problem you are having?
I've got almost everything down, I even managed to teach myself 2D arrays for this, and the snake collides with the edges of the board alright. But I can't get the head to collide with the body properly. :/


Describe what you have tried to solve this problem
I've tried plenty of if statements within two for loops, with every 'if' I tried having many varieties of requirements that must be met to say you lost, and all basically just checking if the head's coordinates are the same as the coordinates of any body block. But for some reason, when I try something like that, the snake's head 'collides' with itself when there is only one blank block between it and any body blocks.

I've also tried setting the coordinates of all the body blocks as 1 the same value I set the border tiles to) on the main grid with a similar if-statement-within-two-for-loops structure, but I can't figure out how to make that temporary and set each tile back being empty (0) when there are no more body blocks in it.

I've looked through so many threads about snake help and collision tutorials around here that my brain hurts, but I can't seem to find anything that helps me out.

...Keep in mind that this year I'm taking my first compsci class in my life, so even if the answer seems obvious to you I'm probably having trouble because I am a programming newb.

Post any relevant code (You may choose to attach the file instead of posting the code if it is too long)

If you decide to run it, use the w, a, s, and d keys to move the snake. (Just in case you skim over that part. )

Also, keep in mind that eventually I will be adding my own simple sprites and things once I sort out this problem, so I need help finding a solution that can be made to work with images too.

Turing:

% declare variables and constants var window : int := Window.Open ("graphics:500;500") var grid : array 0 .. 39, 0 .. 39 of int var score : int := 0 var body_x, body_y : flexible array 1 .. 1 of int var arrows : array char of boolean var direction : int := 0 var food_x, food_y : int := Rand.Int (1, 38) var player_x, player_y : int := 20 const width : int := 12 % set the grid's values for x : 0 .. 39     for y : 0 .. 39         grid (x, y) := 0     end for end for for x : 0 .. 39     grid (x, 0) := 1     grid (x, 39) := 1 end for for y : 0 .. 39     grid (0, y) := 1     grid (39, y) := 1 end for View.Set ("offscreenonly") loop     % redraw the grid     for x : 0 .. 39         for y : 0 .. 39             if grid (x, y) = 1 then                 Draw.FillBox (x * width, y * width, x * width + width, y * width + width, red)             end if         end for     end for     locate (1, 1)     put "Score: ", score     % draw snake's body     for decreasing a : upper (body_x) .. 2         body_x (a) := body_x (a - 1)         body_y (a) := body_y (a - 1)         Draw.FillBox (body_x (a) * width, body_y (a) * width, body_x (a) * width + width,             body_y (a) * width + width, brightgreen)         Draw.Box (body_x (a) * width, body_y (a) * width, body_x (a) * width + width,             body_y (a) * width + width, black)     end for     body_x (1) := player_x     body_y (1) := player_y     Draw.FillBox (body_x (1) * width, body_y (1) * width, body_x (1) * width + width,         body_y (1) * width + width, brightgreen)     Draw.Box (body_x (1) * width, body_y (1) * width, body_x (1) * width + width,         body_y (1) * width + width, black)     % set movement direction     Input.KeyDown (arrows)     if arrows ('a') and direction not= 2 then         direction := 1     elsif arrows ('d') and direction not= 1 then         direction := 2     elsif arrows ('s') and direction not= 4 then         direction := 3     elsif arrows ('w') and direction not= 3 then         direction := 4     end if     % check if snake has hit edge     if direction = 1 and grid (player_x - 1, player_y) = 1 then         exit     elsif direction = 2 and grid (player_x + 1, player_y) = 1 then         exit     elsif direction = 3 and grid (player_x, player_y - 1) = 1 then         exit     elsif direction = 4 and grid (player_x, player_y + 1) = 1 then         exit     end if     % move snake     if direction = 1 and grid (player_x - 1, player_y) = 0 then         player_x -= 1     elsif direction = 2 and grid (player_x + 1, player_y) = 0 then         player_x += 1     elsif direction = 3 and grid (player_x, player_y - 1) = 0 then         player_y -= 1     elsif direction = 4 and grid (player_x, player_y + 1) = 0 then         player_y += 1     end if     % add to the score, regenerate the food, grow the snake     if player_x = food_x and player_y = food_y then         score += 1         food_x := Rand.Int (1, 38)         food_y := Rand.Int (1, 38)         new body_x, upper (body_x, 1) + 1         new body_y, upper (body_y, 1) + 1     end if     % draw food     Draw.FillBox (food_x * width, food_y * width, food_x * width + width,         food_y * width + width, purple)     % draw snake's head     Draw.FillBox (player_x * width, player_y * width, player_x * width + width,         player_y * width + width, green)     Draw.Box (player_x * width, player_y * width, player_x * width + width,         player_y * width + width, black)     View.Update     delay (100)     cls end loop

Please specify what version of Turing you are using
4.1, because of 4.1.1's weird .exe bugs.

As a relatively unimportant sidenote: I plan to make this Doctor Who themed somehow once it's done, as part of a much larger project I've decided to tackle out of boredom. So if anyone has any ideas on what I could make the snake, food, etc look like when I add in the images, please share!

[Dragon20942]

Keep track of all of the snake parts' coordinates so that you can check if the snake is moving into an occupied grid. I understand this is what you've been doing for the boundaries. The boundaries can be changed by checking the direction and whether the head is in the upper or lower bound of the array.

[Kaykao]

Ah... Your advice nudged me in the right direction and now it works. Thank you Dragon, that was an immense help.

In case anyone is curious, these are the key things I added (mind you the program has been modified a LOT since I posted this...):

Turing:

var lives : int := 4 % ... other code here ... % check if snake has hit itself     for a : 2 .. upper (body_x)         if grid (player_x - 1, player_y) = grid (body_x (a), body_y (a)) then             lives -= 1             % code for resetting the snake goes here, taken out             % so as not to bore you all...         end if     end for     % check if snake is 'dead'     if lives = 0 then         exit     end if