10 HOME
20 LET L = 1               : REM SNAKE STARTS WITH LENGTH 1
30 LET W = 40 : LET H = 24 : REM WIDTH AND HEIGHT
35 LET G = 0               : REM BOOL FOR WHEN SNAKE SHOULD GROW
40 GOSUB 2000              : REM INITIALIZE FOOD
41 G = 0                   : REM HACK: RESET GROW STATE
49 LET MX = 100            : REM MAX SIZE OF SNAKE
50 DIM X(MX) : DIM Y(MX)   : REM INTIALIZE ARRAY
51 LET S = 0               : REM INIT SNAKE HEAD INDEX
52 LET T = 0               : REM INIT SNAKE TAIL INDEX
53 LET PX = 20             : REM INIT PREVIOUS HEAD VALUES FOR QUICK REF
54 LET PY = 12
60 X(S) = PX : Y(S) = PY   : REM HEAD AND TAIL START POSITION ARE SAME
61 X(T) = PX : Y(T) = PY

65 REM MAIN LOOP
70 GOSUB 3000
80 FOR N = 1 TO 1000 : NEXT N
90 GOTO 70

999  REM READ KEYBOARD INPUT
1000 LET K = PEEK(49152)
1009 X(S) = PX : Y(S) = PY  : REM INIT NEXT VALUES TO CURRENT VALUES
1010 IF K = 196 THEN X(S) = PX + 1
1020 IF K = 193 THEN X(S) = PX - 1
1030 IF K = 215 THEN Y(S) = PY - 1
1040 IF K = 211 THEN Y(S) = PY + 1
1050 RETURN

1990 REM CREATE FOOD
2000 LET FX = INT(RND(1) * W)
2010 LET FY = INT(RND(1) * H)
2020 HTAB FX : VTAB FY
2030 PRINT "F"
2031 G = 1                  : REM PRESUME SNAKE SHOULD GROW
2040 RETURN

2990 REM DISPLAY SNAKE
3000 IF G = 1 GOTO 3011     : REM GROW BY NOT ERASING TAIL
3002 HTAB X(T) : VTAB Y(T)
3003 T = T + 1              : REM INCREASE TAIL INDEX
3004 IF T = MX THEN T = 0   : REM WRAP INDEX TO 0
3010 PRINT " "
3011 G = 0                  : REM RESET GROW BOOL
3020 REM IF L > 1 THEN GOSUB 5000
3021 S = S + 1              : REM INCREASE HEAD INDEX
3022 IF S = MX THEN S = 0   : REM WRAP INDEX TO 0
3030 GOSUB 1000             : REM DETERMINE NEXT HEAD COORDS
3031 PX = X(S) : PY = Y(S)  : REM COPY HEAD VALUES FOR NEXT LOOP
3040 REM IF X(L) = FX AND Y(L) = FY THEN GOSUB 4000
3041 IF X(S) = FX AND Y(S) = FY THEN GOSUB 4000
3042 HTAB X(S) : VTAB Y(S)
3043 PRINT "S"
3044 RETURN                 : REM SKIP OLD LOGIC
3050 FOR I = 1 TO L
3060 HTAB X(I) : VTAB Y(I)
3070 PRINT "S"
3080 NEXT I
3090 RETURN

3990 REM GROW SNAKE
4000 L = L + 1
4010 X(L) = X(L - 1)
4020 Y(L) = Y(L - 1)
4030 GOSUB 2000
4040 RETURN

4990 REM SHIFT SNAKE ARRAY
5000 FOR I = 1 TO L - 1
5010 X(I) = X(I + 1)
5020 Y(I) = Y(I + 1)
5030 NEXT I
5040 RETURN