CODE <constant string> is broken (*solved*)

[boriel]

Well, I have fixed the "0909"(F to F) problem. It works now.

Regarding your program, I've managed to work, making this changes:

• "0909"(F to F) can now be written as "0909"(F) (By the way, BASIN v15 does not accept this syntax, whilst Sinclair's BASIC does)
  
• Y coordinate for PLOT in Line 6 in your code lacks an ABS (it takes negative values). Surprisingly, Sinclair BASIC accepts negative values for PLOT if they are within range. So PLOT -1, -2 is right!. ZX Basic will do either, but will plot in a different position. Better use ABS for Y coordinate too.
  
• PLOT, DRAW, and CIRCLE takes the entire screen, this means they work in the vertical range 0..192. And the result will be "shifted" down 16 pixels. So PLOT x, y in Sinclair BASIC should be PLOT x, y + 16 in ZX BASIC if you want exactly the same picture (otherwise, it doesn't matter). In this case, if you don't plot at y+16, the numbers printed will be out of the drawings.
  
• For the strings, the index starts in 0, not in 1. So the "0909"(1) returns "9", not "0". Better use "-0909"(F) or "0909"(F - 1). The former is preferred, faster and takes less memory. The 1st character is dummy (ignored).
  
• The biggest problem: You're having Overflows in the coordinates calculations. CODE "a" returns an unsigned byte, but you multiply, add, etc... and get values outside the range 0..255. Better make a typecast to a wider data type, like Integer: CAST(INTEGER, CODE "-0909"(f)) should do the trick.

Here you are the modified listing:

Code:

DIM f,g as UBYTE

1  PRINT AT 9,9;"SIMON"
3  FOR f=1 TO 4
4     INK f
5     FOR g=1 TO 32
6         PLOT INT ABS((SGN (f-2.5)*CAST(INTEGER, 80))+24+g), 16 + INT ABS (((CAST(INTEGER, CODE "-0202"(f))-49)*99)-48+g)
7         DRAW 32,0
8     NEXT g
9     goto 11
10  STOP
11  PRINT INK f; OVER 1;AT CODE "-1919"(f)-44,CODE "-0099"(f)-41;f
12     NEXT f
13  LET f=1
goto 4

The mayor change is Line 6 (Notice 16 + INT ABS in y coord). The program crash was due to bug in version <1.1.9 (now available for download). Also notice the "-" char before every string, and notice that (f TO f) becomes (f) for better legibility.