void Tfrm_BelongFunction::DrawFunction(TCanvas*m_canvas,TRect&m_rect)
{
   TPenStyle style = m_canvas->Pen->Style;
   TColor color =  m_canvas->Pen->Color;
   m_canvas->Pen->Style = psSolid;
   m_canvas->Pen->Color =clBlue;


   if(begin==end)
     return;
   AnsiString str = m_strExpress+"[-10,10]";
   DrawFunction(m_canvas,m_rect,str);
//////////////////////////////

//
   int sizegrid = 30;
   double dis = (end-begin)/M;
   for(double i=0;i<=M;i++)
   {
       AnsiString str;
       str = FloatToStr(begin+dis*i);
       str = str.FormatFloat("0.00",begin+dis*i);
       m_canvas->TextOutA(m_rect.Left+i*sizegrid-5,m_rect.Bottom+5,str);
   }

   m_canvas->Pen->Style = style;
   m_canvas->Pen->Color = color;

}