[c++] VC基本概念

1. ClassView、ResourceView、FileView有什么联系和区别？ClassView中显示类，ResourceView中显示各种控件句柄，FileView中显示各种文件（.h和.cpp）
2. 两种访问方法：对象实例化，指针实例化
3. 二元关系：类与对象，声明与定义，属性与方法，.h与.cpp文件，地址与内容，局部与全局

void CMFCApplication3Dlg::DrawCircle(CDC *pDC,CRect &rectPicture,double x1, double y1, double x2, double y2,color a)
{
    // TODO: 在此添加控件通知处理程序代码
    CPen newPen;
    CPen *pOldPen;
    
    newPen.CreatePen(PS_SOLID, 3, RGB(a.r,a.g,a.b));
    pOldPen = pDC->SelectObject(&newPen);
    pDC->SelectStockObject(NULL_BRUSH);
    pDC->Ellipse(x1, y1, x2, y2);
    //pDC->MoveTo(rectPicture.left, rectPicture.bottom);
    //pDC->LineTo(rectPicture.left + 50, rectPicture.bottom - 100);
    pDC->SelectObject(pOldPen);
    newPen.DeleteObject();
}