VC++帮我理解一下使图形变化的算法

voidCMfc1View::OnDraw(CDC*pDC)

{

x05CMfc1Doc*pDoc=GetDocument();

x05ASSERT_VALID(pDoc);

x05//TODO:adddrawcodefornativedatahere

x05//清除当前图形

x05CBrushmybrush1;

x05mybrush1.CreateSolidBrush(RGB(255,255,255));

x05CRectmyrect1(0,0,1024,768);

x05pDC->FillRect(myrect1,&mybrush1);

x05//判断当前图形ituxing

/*x05if(ituxing==1)

x05//ituxing=1,画矩形

x05x05pDC->Rectangle(20,20,89,89);

x05elseif(ituxing==2)

x05//ituxing=2,画圆

x05x05x05pDC->Ellipse(20,20,89,89);

x05else

x05//否则,画三角形

x05x05{

x05x05x05pDC->MoveTo(20,20);

x05x05x05pDC->LineTo(89,45);

x05x05x05pDC->LineTo(20,89);

x05x05x05pDC->LineTo(20,20);

x05x05}*/

x05pDC->Ellipse(30*ituxing,30*ituxing,30*ituxing+50,30*ituxing+50);

x05//TODO:adddrawcodefornativedatahere

}

voidCMfc1View::OnTimer(UINTnIDEvent)

{

x05//TODO:Addyourmessagehandlercodehereand/orcalldefault

x05//获取指针pdc

x05if(nIDEvent==1)

x05{

x05ituxing=(ituxing+1)%10;

x05CDC*pDC=GetDC();

x05//调用OnDraw(pDC)重画

x05OnDraw(pDC);

x05//使ituxing循环

ituxing=(ituxing+1)%3;

x05}

x05

x05CView::OnTimer(nIDEvent);

}

intCMfc1View::OnCreate(LPCREATESTRUCTlpCreateStruct)

{

x05if(CView::OnCreate(lpCreateStruct)==-1)

x05x05return-1;

x05//TODO:Addyourspecializedcreationcodehere

x05//设置更新时间

x05SetTimer(1,1000,NULL);

x05return0;

}

提问：怎么理解ituxing=(ituxing+1)%3;这行呢.ituxing也不是个随机数啊?