Fix issues #1, #4

From suggestions by @badvision: Added the POKE call to get all 24 lines, and the semicolons seem to have fixed the occasional line which somehow advanced the whole screen. Also added more comments and removed leading spaces

MATRIX

@@ -1,35 +1,44 @@
- 1 REM THE MATRIX
- 2 REM BY NEIL KANDALGAONKAR <NEILK@NEILK.NET>
- 3 REM https://github.com/neilk/apple-ii-matrix/
- 5 FOR I = 1 TO 30: PRINT " ": NEXT I
- 10 DIM K(3,2)
- 11 H = 0
- 12 V = 1
- 13 F = 2
- 15 FOR C = 0 TO 3
- 16 GOSUB 50
- 17 NEXT C
- 20 FOR C = 0 TO 3
- 30 R =  INT ( RND (1) * 20)
- 31 IF R = 1 THEN  GOSUB 50
- 32 IF R >< 1 THEN  GOSUB 100
- 35 NEXT C
- 39 GOTO 20
- 50 REM  RESET
- 51 K(C,H) =  INT ( RND (1) * 40) + 1
- 52 K(C,V) = 0
- 53 K(C,F) =  INT ( RND (1) * 2)
- 99  RETURN
- 100 REM  DRAW
- 101 K(C,V) = K(C,V) + 1
- 102 IF K(C,V) > 22 THEN  RETURN
- 103 VTAB K(C,V): HTAB K(C,H)
- 110 IF K(C,F) = 1 THEN  GOSUB 120
- 111 IF K(C,F) = 0 THEN  GOSUB 130
- 119 RETURN
- 120 REM  DRAW CHAR
- 121 PRINT  CHR$ ( INT ( RND (1) * 96 + 32))
- 122 RETURN
- 130 REM  ERASE CHAR
- 131 PRINT " "
- 132 RETURN
+1 REM  THE MATRIX
+2 REM  BY NEIL KANDALGAONKAR <neilk@neilk.net>
+3 REM  https://github.com/neilk/apple-ii-matrix/
+4 REM  CLEAR SCREEN
+5 FOR I = 1 TO 30: PRINT: NEXT I
+6 REM  USE ALL 24 LINES
+7 POKE 35, 25
+9 REM  SET UP THREE CURSORS
+10 DIM K(3,2)
+11 REM  CONSTANTS FOR ARRAY INDICES. 
+12 REM  HORIZONTAL, VERTICAL, DRAW/ERASE
+13 H = 0: V = 1: F = 2
+14 REM RESET ALL CURSORS
+15 FOR C = 0 TO 3
+16 GOSUB 50
+17 NEXT C
+20 REM  MAIN LOOP
+21 REM  DRAW CURSORS FOREVER. 5% CHANCE OF RESET
+30 FOR C = 0 TO 3
+31 R =  INT ( RND (1) * 20)
+32 IF R = 1 THEN  GOSUB 50
+33 IF R >< 1 THEN  GOSUB 100
+35 NEXT C
+39 GOTO 30
+50 REM  RESET A CURSOR
+51 REM  AT A RANDOM SPOT AT THE TOP OF THE SCREEN
+52 REM  50-50 CHANCE OF DRAWING OR ERASING
+53 K(C,H) =  INT ( RND (1) * 40) + 1
+54 K(C,V) = 0
+55 K(C,F) =  INT ( RND (1) * 2)
+59  RETURN
+100 REM  ADVANCE CURSOR AND DRAW SOMETHING
+101 K(C,V) = K(C,V) + 1
+102 IF K(C,V) > 24 THEN  RETURN
+103 VTAB K(C,V): HTAB K(C,H)
+110 IF K(C,F) = 1 THEN  GOSUB 120
+111 IF K(C,F) = 0 THEN  GOSUB 130
+119 RETURN
+120 REM  RANDOM CHAR
+121 PRINT  CHR$ ( INT ( RND (1) * 96 + 32));
+122 RETURN
+130 REM  ERASE CHAR
+131 PRINT " ";
+132 RETURN