求助！！高手请进！

请教一个关于VC的问题，我做了个绘图区（IDC_ht），我想让绘图区里的曲线随着变量m_uain的值变化而变化，以下是我的程序，但不知为何，测试时绘图区里没有曲线，请高手赐教。
void CWyqDlg::ondraw()//绘图
{
int k=num-1;
    CWnd* pWnd=GetDlgItem(IDC_ht);
CRect rect;
pWnd->GetClientRect(rect);
CDC* pDC=pWnd->GetDC();
CPen* pNewPen=new CPen;
pNewPen->CreatePen(PS_SOLID,2,RGB(255,0,0));
CPen* pOldPen=pDC->SelectObject(pNewPen);
if(k>=1)
{
pDC->MoveTo((k-1),rect.bottom-(int)(5*m_data[k-1]));
    pDC->LineTo(k,rect.bottom-(int)(5*m_data[k]));
    pDC->SelectObject(pOldPen);
}
else
    {  
pDC->MoveTo(k,rect.bottom-(int)(5*m_data[0]));
    pDC->LineTo(k,rect.bottom-(int)(5*m_data[0])); 
    }

    if(k>=rect.right-5)
{    
         renew();
 pDC->MoveTo(0,100);
}
   delete pNewPen;
}void CWyqDlg::renew()//刷新
{   
CWnd *pWnd=GetDlgItem(IDC_ht);
pWnd->UpdateWindow();
CDC *pDC=pWnd->GetDC();
CBrush rebrush;
rebrush.CreateSolidBrush(RGB(255,255,255));
CBrush *pOldBrush=pDC->SelectObject(&rebrush);
CPen *PNewPen=new CPen;
PNewPen->CreatePen(PS_SOLID,1,RGB(255,255,255));
CPen *POLDPen=pDC->SelectObject(PNewPen);
CRect rect;
pWnd->GetClientRect(rect);
pDC->Rectangle(rect);
pDC->SelectObject(pOldBrush);
pDC->SelectObject(POLDPen);
    delete PNewPen; 
m_uain=0; for(int i=0;i<num;i++)m_data[i]=0;
num=0;
}