Snake by TMCD677

Snake
TMCD677 (tvgames.me)
Locomotive BASIC v1.1
PUR-120

Introduction
------------
My first attempt at writing a complete game limited to 10 Lines.  Chosen Locomotive BASIC (Amstrad CPC)
for auld lang syne.  Pretty simple game many will remember from their old Nokia mobile phones in the
early 2000's.  Code is under 800 characters but a couple of lines squeek over 80 characters hence PUR-120.
Game would easily be PUR-80 in just about anyother 8-bit dialect.

Controls
--------
Please make sure your keyboard is in lowercase mode (default) prior to running the game.

            UP    -  'p'
            DOWN  -  'l'
            LEFT  -  'z'
            RIGHT -  'x'

Instructions
------------
The game starts with a small single segment snake in the centre of the screen automatically moving to the
left.  Your task is to guide this snake around the screen eating numbers that will appear randomly
around the screen.  Each time you eat a number your snakes body will grow by that number of segments.

However you need to be careful.  The snake cannot move beyond the edges of the screen or cross its own
path.  Hit the edge of the screen or the growing body of the snake and it's GAME OVER!  Beware - the top
of the screen is at Line2, below the score line.  Also, each time you eat a number the snakes movement 
will speed up by that amount.

When the game ends press any key to return to Locomotive BASIC and execute:

     RUN

for another game.

Scoring
-------
Snake is a high score challenge game.  Who lasts the longest and eats the most numbers gets the highest
score and wins.  You score 10pts each time the snake moves and the value of any numbers the snake eats.

Disk Catalogue
--------------
     
     Snake1.BAS     -     Original 5 line concept test moving snake body around screen
     Snake2.BAS     -     1st attempt long listing; snake doesn't move; numbers appear randomly
     Snake3.BAS     -     10Liner version of Snake2
     Snake4.BAS     -     10Liner.  Displays snake head, first random number, then hits GAME OVER
     Snake5.BAS     -     Full anotated listing.  Random numbers and snake growth are broken
     Snake6.BAS     -     Fully working game, final full anotated listing - see listin below
     Snake7.BAS     -     Fully working game. Snake 6 condensed.  REM statments removed and variable names shortened
     Snake8.BAS     -     10Liner. Fully working game.  Final fully working entry - see listing below

Fully Anotated Listing
----------------------

    10 REM VARIABLES
    20 DIM path(500,2)             : REM snake body path co-ordinates stack
    30 LET tsp=1                   : REM tail stack pointer
    40 LET hsp=1                   : REM head stack pointer
    50 LET x=10                    : REM head x-axis co-ordinate
    60 LET y=10                    : REM head y-axis co-ordinate
    70 LET i$=""                   : REM user input
    80 LET score=-10               : REM player score
    90 LET grow=0                  : REM amount to grow snake by
    100 LET c$=""                  : REM screen content
    110 LET w=750                  : REM wait time, snake speed
    120 LET n=0                    : REM random number
    130 LET d$="z"                 : REM current direction
    140 LET nx=0                   : REM random number x-axis co-ordinate
    150 LET ny=0                   : REM random number y-axis co-ordinate
    160 LET temp$=""               : REM screen contents
    170 LET flag=1                 : REM random number display flag

    200 REM SET-UP
    210 MODE 0                     : REM 20 characters x 25 lines
    220 INK 0,1                    : REM background colour (blue)
    230 INK 1,24                   : REM snake colour (yellow)
    240 INK 2,26                   : REM score colour (white)
    250 INK 3,6                    : REM number colour (red)
    260 INK 4,6,26                 : REM game over colour (flashing red+white)

    300 REM START GAME LOOP
    310 LET path(hsp,1)=x          : REM store head x-axis in stack
    320 LET path(hsp,2)=y          : REM store head y-axis in stack
    330 LET hsp=hsp+1              : REM increase head stack pointer
    340 IF hsp>500 THEN hsp=1      : REM if head stack point at end of stack move to start

    500 REM DISPLAY
    510 LOCATE x,y                 : REM goto new head position
    520 PEN 1                      : REM use yellow ink
    530 PRINT "*";                 : REM display snake head
    540 LET score=score+10         : REM add 10 to score for each move
    550 PEN 2                      : REM use white ink
    560 LOCATE 12,1                : REM goto score display position
    570 PRINT score;               : REM update score
    580 FOR s=1 TO w:NEXT s        : REM wait for snake speed
    590 IF grow<>0 THEN LET grow=grow - 1 ELSE LOCATE path(tsp,1),path(tsp,2):PRINT " ";:LET tsp=tsp+1:IF         tsp>500 THEN LET tsp=1
    595                              REM if snake not growing then remove body from current tail position

    700 REM USER INPUT AND MOVEMENT
    710 LET i$=INKEY$              : REM get user input
    720 IF i$<>"" THEN LET d$=i$   : REM if input detected update direction
    730 IF d$="z" THEN LET x=x-1   : REM if user presses "z" move left
    740 IF d$="x" THEN LET x=x+1   : REM if user presses "x" move right
    750 IF d$="p" THEN LET y=y-1   : REM if user presses "p" move up
    760 IF d$="l" THEN LET y=y+1   : REM if user presses "l" move down

    800 REM COLLITION DETECTION
    810 IF x<1 OR x>20 OR y<2 OR y>25 THEN GOTO 1000
    815                              REM end game if hit edge of screen
    820 LOCATE x,y                 : REM goto next head position
    830 LET temp$=COPYCHR$(#0)     : REM get any characters currently at that position
    840 IF temp$="*" THEN GOTO 1000: REM end game if snake head touches body
    850 IF temp$<>" " THEN LET grow=n:LET score=score+n:LET w=w-n:LET flag=1
    855                              REM if head finds number add to score and grow snake

    900 REM RANDOM NUMBERS
    910 IF flag=0 THEN GOTO 300    : REM if not collected next number
    920 LET n=INT((RND(1)*9)+1)    : REM choose a random numner (1..9)
    930 LET nx=INT((RND(1)*20)+1)  : REM choose random x co-ordinate for random number
    940 LET ny=INT((RND(1)*25)+1)  : REM choose random y co-ordinate for random number
    950 IF ny=1 THEN GOTO 930      : REM if y-cordinate on score line choose another
    960 LOCATE nx,ny               : REM goto chosen random number position
    970 LET temp$=COPYCHR$(#0)     : REM get any characters already there
    980 IF temp$="*" THEN GOTO 930 : REM choose new location if snake body is there
    990 PEN 3:PRINT n;: LET flag=0 : REM display new random number if needed

    999 GOTO 300                   : REM back to start of game loop

    1000 REM GAME OVER             
    1010 PEN 4                     : REM use flashing ink
    1020 LOCATE 2,10               : REM centre message on screen
    1030 PRINT "G A M E   O V E R";: REM display game over message
    1040 LET i$=inkey$             : REM get user input
    1050 IF i$="" THEN GOTO 1040   : REM keep waiting until user presses a key
    1060 PEN 1                     : REM use default OS ink colour 

Final 10 Liner Listing
----------------------

1 DIM p(500,2):t=1:h=1:x=10:y=10:s=-10:m=750:d$="z":f=1:MODE 0:INK 2,26:INK 3,6:INK 4,6,26                 
2 p(h,1)=x:p(h,2)=y:h=h+1:LOCATE x,y:PEN 1:?"*";:s=s+10:PEN 2:LOCATE 12,1:? s;:FOR z=1 TO m:NEXT:IF h>500 THEN h=1   
3 IF g<>0 THEN g=g-1 ELSE LOCATE p(t,1),p(t,2):?" ";: t=t+1:IF t>500 THEN t=1                
4 i$=INKEY$:IF i$<>"" THEN d$=i$                    
5 IF d$="z" THEN x=x-1 ELSE IF d$="x" THEN x=x+1 ELSE IF d$="p" THEN y=y-1 ELSE IF d$="l" THEN y=y+1
6 IF x<1 OR x>20 OR y<2 OR y>25 THEN GOTO 10
7 LOCATE x,y:c$=COPYCHR$(#0):IF c$="*" THEN GOTO 10 ELSE IF c$<>" " THEN g=g+n:s=s+n:m=m-n:f=1 
8 IF f=0 THEN GOTO 2 ELSE n=INT((RND(1)*9)+1):v=INT((RND(1)*20)+1):w=INT((RND(1)*25)+1):IF w=1 THEN GOTO 8
9 LOCATE v,w:c$=COPYCHR$(#0):IF c$="*" THEN GOTO 8 ELSE PEN 3:? n;:f=0:GOTO 2
10 PEN 4:LOCATE 2,10:?"G A M E   O V E R";:i$=inkey$:IF i$="" THEN GOTO 10 ELSE PEN 1