//x must be global.
//Might as well make y global.

F64 x,y,y_last;

U0 Cartesian()
{
  U8 *st;
  I64 ch=0,h,v;
  Bool first;
  CDC *dc=DCAlias;
  do
  {
    DocClear;
    "Enter algebraic equation to graph.\n"
    "Example: y=2*x\n"
    "y=";
    if (st=GetStr)
    {
      if (*st)
      {
        h=Fs->pix_width/2;
        v=Fs->pix_height/2;
        dc->color=RED;
        GrLine(dc,h,0,h,2*v+1);
        GrLine(dc,0,v,2*h+1,v);
        first=TRUE;
        dc->color=BLACK;
        for (x=-h; x<=h; x++)
        {
          y=-ExePrint("ToF64(%s);",st)(F64);
          if (!first)
            GrLine(dc,x-1+h,y_last+v,x+h,y+v);
          y_last=y;
          first=FALSE;
        }
        ch=GetChar;
      }
      else
        ch=CH_SHIFT_ESC;
      Free(st);
    }
    else
      ch=CH_SHIFT_ESC;
    DCFill;
  }
  while (ch!=CH_SHIFT_ESC && ch!=CH_ESC);
  DCDel(dc);
}

Cartesian;

//For better performance, compile the expression entered by the
//user one time with LexExpression2Bin() and use Call().
//See ::/Demo/CompileDemo.HC.