/*REXX program  plots  three circles  using  midpoint/Bresenham's circle algorithm.     */
@.= '·'                                          /*fill the array with middle─dots char.*/
minX=0;     maxX=0;      minY=0;     maxY=0      /*initialize the minimums and maximums.*/
call drawCircle   0,   0,   8,   '#'             /*plot 1st circle with pound character.*/
call drawCircle   0,   0,  11,   '$'             /*  "  2nd    "     "  dollar    "     */
call drawCircle   0,   0,  19,   '@'             /*  "  3rd    "     "  commercial at.  */
border=2                                         /*BORDER:  shows  N  extra grid points.*/
minX=minX-border*2;   maxX=maxX+border*2         /*adjust min and max  X  to show border*/
minY=minY-border  ;   maxY=maxY+border           /*   "    "   "   "   Y   "   "     "  */
if @.0.0==@.  then @.0.0='┼'                     /*maybe define the plot's axis origin. */
                                                 /*define the plot's horizontal grid──┐ */
  do h=minX  to maxX;  if @.h.0==@.  then @.h.0='─';  end              /* ◄───────────┘ */
  do v=minY  to maxY;  if @.0.v==@.  then @.0.v='│';  end              /* ◄──────────┐  */
                                                 /*define the plot's vertical grid───┘  */
     do y=maxY  by -1  to minY;   _=             /* [↓]  draw grid from  top ──► bottom.*/
             do x=minX  to maxX;  _=_ || @.x.y   /* ◄───   "    "    "  left ──► right. */
             end   /*x*/                         /* [↑]  a grid row should be finished. */
     say _                                       /*display a single row of the grid.    */
     end           /*y*/
exit                                             /*stick a fork in it,  we're all done. */
/*──────────────────────────────────────────────────────────────────────────────────────*/
drawCircle: procedure expose @. minX maxX minY maxY
            parse arg xx,yy,r 1 y,plotChar;     fx=1;     fy=-2*r  /*get X,Y coördinates*/
            f=1-r
                    do x=0  while  x<y  /*▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒*/
                    if f>=0  then  do;  y=y-1;  fy=fy+2;  f=f+fy;  end               /*▒*/
                                                fx=fx+2;  f=f+fx                     /*▒*/
                    call plotPoint  xx+x,  yy+y                                      /*▒*/
                    call plotPoint  xx+y,  yy+x                                      /*▒*/
                    call plotPoint  xx+y,  yy-x                                      /*▒*/
                    call plotPoint  xx+x,  yy-y                                      /*▒*/
                    call plotPoint  xx-y,  yy+x                                      /*▒*/
                    call plotPoint  xx-x,  yy+y                                      /*▒*/
                    call plotPoint  xx-x,  yy-y                                      /*▒*/
                    call plotPoint  xx-y,  yy-x                                      /*▒*/
                    end   /*x*/         /* [↑]  place plot points ══► plot.▒▒▒▒▒▒▒▒▒▒▒▒▒*/
            return
/*──────────────────────────────────────────────────────────────────────────────────────*/
plotPoint:  parse arg c,r;     @.c.r=plotChar    /*assign a character to be plotted.    */
            minX=min(minX,c);  maxX=max(maxX,c)  /*determine the minimum and maximum  X.*/
            minY=min(minY,r);  maxY=max(maxY,r)  /*    "      "     "     "     "     Y.*/
            return