... level.

I have a block of byte data allocated ... I load from tape a block bytes containing some ... character data:

LET a$(pos to pos+1)=s ... , 1 TO 2)
LET a$(pos+32 to pos+33 ... , I paint in correct position a$ "tile"...
7- If ...

... that particular demo.

A couple of extra notes:
[list]
[*]If assigning a slice ( which the demo is ... in 768 ) don't use "LET a$(a TO b)=string expression" (it ... match the slice and use "LET a$=string expression".
[*]Because of ...

... very well looking at LET A 12 or LET K 0 but you ...

... (a+1)
12 RESTORE 11: DIM v$(20*32): LET da ... =FN p(23639)+8
13 RANDOMIZE FN a("a"(1)): LET ... pa=23563: LET pv=da: GO SUB ... : GO SUB 90
17 LET a$=v$(TO 160): STOP

...
[CODE]640 LET dio=64440
920 LET dir=61000
LET enemy=enemy+1
970 LET a$(pos TO pos+1)=s ... TO 2)
980 LET a$(pos+32 TO pos+33 ... TO 4)
990 LET dir=dir+1
... 1010 NEXT x
1020 LET pos=pos+32
...

... STEP 16: LET u=t: LET b$="":
FOR a=1 TO 31 ... STEP 2: LET b ... $=b$+t$(u)+t$(u): LET u=u+1: NEXT a ... :
LET v$=v$+b ... $+b$: [strike]LET v=v ...

... STEP 16: LET u=t: LET b$="":
FOR a=1 TO 31 ... STEP 2: LET b ... $=b$+t$(u)+t$(u): LET u=u+1: NEXT a ... :
LET v$=v$+b ... $+b$: LET v=v+64 ...

... 290 LET v$=""
300 LET a$=""
305 LET b$=""
310 LET x ... 40000 TO 40159
350 LET a$=a$+g$(PEEK (n))
... 355 LET b$=b$+g$(PEEK (n ... )+1)
360 LET x=x+1
370 ... x=16 THEN LET v$=v$+a$+b$:LET a$="":LET b$="":LET x=0

... LET v$=""
300 LET a$=" ": REM 32 spaces
305 LET ... b$=" "
310 LET x ... TO 40159
350 LET a$(x to x+1)= ...

... ]
...
10 LET a=bytes: LET iv=0: LET bt=0: DIM n ... d=1 TO 5: LET n(d)=PEEK (a+d): NEXT d ... ; FLASH ynk=2;number;: PRINT "]";: LET a=a+6: GO TO 21
...
2000 LET v$="":
FOR d=a-1 TO bytes ...