RosettaCodeData/Task/Mandelbrot-set/GW-BASIC/mandelbrot-set.basic

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10 SCALE# = 1/60 : ZEROX = 160
20 ZEROY = 100 : MAXIT = 32
30 SCREEN 1
40 FOR X = 0 TO 2*ZEROX - 1
50 CR# = (X-ZEROX)*SCALE#
60 FOR Y = 0 TO ZEROY
70 CI# = (ZEROY-Y)*SCALE#
80 ZR# = 0
90 ZI# = 0
100 FOR I = 1 TO MAXIT
110 BR# = CR# + ZR#*ZR# - ZI#*ZI#
120 ZI# = CI# + 2*ZR#*ZI#
130 ZR# = BR#
140 IF ZR#*ZR# + ZI#*ZI# > 4 THEN GOTO 170
150 NEXT I
160 GOTO 190
170 PSET (X, Y), 1 + (I MOD 3)
180 PSET (X, 2*ZEROY-Y), 1+(I MOD 3)
190 NEXT Y
200 NEXT X