Out of memory when using uinteger array (*solved*)

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Code:

' tn = TriangleNumber, mt = MaximumTriangles (# of), rn = RandomNumber, GraphicWidth, GraphicHeight, zn = ZeroNumber (Modifier)
INK 6: PAPER 1: FLASH 0: BRIGHT 1: OVER 0: INVERSE 0: DIM tn, mt, rn, gw, gh, znw, znh AS UBYTE: DIM x(4,4) AS UINTEGER: DIM y(4,4) AS UINTEGER
tn=0: mt=0: rn=0: znw=0: znh=16
gw=255: gh=175+znh: BORDER 1: CLS: PRINT AT 10,5;"The Sierpinski Triangle";: tn=1: mt=4 '256-1 '176-1
x(tn,1)=znw: y(tn,1)=znh: x(tn,2)=gw/2: y(tn,2)=gh: x(tn,3)=gw: y(tn,3)=znh: GOSUB FirstPoint: tn=tn+1
x(tn,1)=znw: y(tn,1)=gh: x(tn,2)=gw/2: y(tn,2)=znh: x(tn,3)=gw: y(tn,3)=gh: GOSUB FirstPoint: tn=tn+1
x(tn,1)=znw: y(tn,1)=gh: x(tn,2)=gw: y(tn,2)=gh/2: x(tn,3)=znw: y(tn,3)=znh: GOSUB FirstPoint: tn=tn+1
x(tn,1)=gw: y(tn,1)=gh: x(tn,2)=znw: y(tn,2)=gh/2: x(tn,3)=gw: y(tn,3)=znh: GOSUB FirstPoint
tn=1: PRINT AT 12,4;"Press any key to continue";
ScanAnyKey:
IF INKEY$="" THEN GO TO ScanAnyKey: END IF
RANDOMIZE : CLS
DrawTriangles:
'rn=RND*3+1
rn=CAST(UINTEGER,RND)*3+1
'rn=CAST(UINTEGER,RND*3)+1
'rn=INT (RND*3)+1
x(tn,4)=(x(tn,4)+x(tn,rn))/2
y(tn,4)=(y(tn,4)+y(tn,rn))/2
PLOT x(tn,4),y(tn,4)
tn=tn+1: IF tn>mt THEN tn=1: END IF
GO TO DrawTriangles
FirstPoint:
x(tn,4)=x(tn,2): y(tn,4)=y(tn,2): RETURN

Crashes the machine after a few pixels and the offending line is the first cast line. The assembly code:

Code:

__LABEL__DrawTriangles:
    call RND
    call __FTOU32REG
    ld de, 3
    call __MUL16_FAST
    inc hl
    ld a, l
    ld (_rn), a

I am trying to get rid of the floating point multiplication in the RND section to gain speed.
The arrays work fine now thanks, and thanks for the DIM answer; reminds me of context within a context.
I had a feeling that those two bugs might be related.

Otherwise, I just checked into the forum as I have been really busy so sorry for the late reply to this thread.