How to emulate a mouse scroll for the current window opened?

How to emulate a mouse scroll for the current window opened?

I'm currently trying to emulate a mouse scroll event on the current window
opened.I'm implementing it using setscrollpos() fucntion in visual C++.
SetScrollPos(hwnd,SB_VERT,0,TRUE);
UpdateWindow(hwnd);
How does one pass the current window opened to the parameter hwnd?