UINT SetTimer(
  HWND hWnd,
  UINT nIDEvent,
  UINT uElapse,
  TIMERPROC lpTimerFunc
);
第二个参数也就是定时器的ID，是自己随便定的吗？只要不重复就行吗？
他触发时是触发整个程序嘛？菜鸟刚学，望多多指教~！

MSDN Library
nIDEvent
[in] Specifies a nonzero timer identifier. If the hWnd parameter is NULL, and the nIDEvent does not match an existing timer then it is ignored and a new timer ID is generated. If the hWnd parameter is not NULL and the window specified by hWnd already has a timer with the value nIDEvent, then the existing timer is replaced by the new timer. When SetTimer replaces a timer, the timer is reset. Therefore, a message will be sent after the current time-out value elapses, but the previously set time-out value is ignored. If the call is not intended to replace an existing timer, nIDEvent should be 0 if the hWnd is NULL.

看不大懂呀！你看我这样可以不？
SetTimer(hwnd,1,500,NULL);

只要非零值，就好了。
表示设定一个与hwnd关联的Timer, 这个Timer的标识是1, 触发时间是0.5s， time-out时在消息队列里放入一个WM_TIMER消息
我也是刚学，如果理解有错，概不负责啊