Petzold example question

[ForRealzZzZ]

Ive been following petzolds book and understanding everything line by line up until this example(Im very OCD about that). Im not very fluent in C I started with C++ and worked my way up, is this C?

y << 8 | x;

and here are the callbacks for the example there is one in the child window creation loop and above the WM_SETFOCUS message callback.

LRESULT CALLBACK WndProc(HWND hwnd, UINT message, LPARAM lParam, WPARAM wParam)
{
	static HWND hwndChild[DIVISIONS][DIVISIONS];
	int			cxBlock, cyBlock, x, y;

	switch(message)
	{
	case WM_CREATE:
		for (x = 0; x<DIVISIONS; x++)
			for(y = 0; y< DIVISIONS; x++)
				hwndChild[x][y] = CreateWindow(szMyChild, NULL,
				WS_CHILDWINDOW| WS_VISIBLE, 0,0, 0, 0, hwnd, (HMENU) (y << 8 | x),(HINSTANCE),GetWindowLong(hwnd, GWLP_HINSTANCE),NULL);
		return 0;
	case WM_SIZE:
		cxBlock = LOWORD (lParam);
		cyBlock = HIWORD (lParam);
		
		for(x = 0; x < DIVISIONS ; x++)
			for( y = 0; y < DIVISIONS; y ++)
					MoveWindow(hwndChild [x][y], 
						x * cxBlock, y * cyBlock,
							cxBlock, cyBlock, TRUE);
		return 0;
	case WM_LBUTTONDOWN:
		MessageBeep(0);
		return 0;
	case WM_SETFOCUS:
		SetFocus( GetDlgItem(hwnd, idFocus));
		return 0;
	case WM_KEYDOWN:
		x = idFocus & 0xFF;
		y = idFocus >> 8;
		switch(wParam){
		case VK_UP:    y--;  break;
		case VK_DOWN:  y++;  break;
		case VK_LEFT:  x--;  break;
		case VK_RIGHT: x++;  break;
		case VK_HOME:  x = y = 0; break;
		case VK_END:   x = y = DIVISIONS - 1; break;
		default: return 0;
		}
		x = (x+DIVISIONS) % (DIVISIONS);
		y = (y +DIVISIONS) % (DIVISIONS);

		idFocus = y<< 8 | x;

		SetFocus(GetDlgItem(hwnd, idFocus));
		return 0;
		
	case WM_DESTROY:
		PostQuitMessage (0);
		return 0;
	}
	return DefWindowProc(hwnd, message, wParam, lParam);
}

LRESULT CALLBACK ChildWndProc(HWND hwnd, UINT message, WPARAM wParam, LPARAM lParam)
{
	HDC hdc;
	PAINTSTRUCT ps;
	RECT rect;
	
	switch(message)
	{
	case WM_CREATE:
		SetWindowLong(hwnd, 0, 0);
		return 0;
	case WM_KEYDOWN:
		if(wParam != VK_RETURN && wParam != VK_SPACE)
		{
			SendMessage(GetParent(hwnd), message, wParam, lParam);
			return 0;
		}
	case WM_LBUTTONDOWN:
		SetWindowLong(hwnd, 0, 1 ^ GetWindowLong(hwnd, 0));
		SetFocus(hwnd);
		InvalidateRect(hwnd,NULL,FALSE);
		return 0;
	case WM_SETFOCUS:
		idFocus = GetWindowLong(hwnd, GWL_ID);
	case WM_KILLFOCUS:
		InvalidateRect(hwnd, NULL, TRUE);
		return 0;
	case WM_PAINT:
		hdc = BeginPaint(hwnd, &ps);
		GetClientRect(hwnd, &rect);
		Rectangle(hdc, 0, 0, rect.right, rect.bottom);

		if(GetWindowLong(hwnd, 0))
		{
			MoveToEx(hdc, 0, 0, NULL);
			LineTo(hdc, rect.right, rect.bottom);
			MoveToEx(hdc, 0, rect.bottom, NULL);
			LineTo(hdc, rect.right, 0);
		}

		if(hwnd == GetFocus())
		{
			rect.left += rect.right / 10;
			rect.right -= rect.left;
			rect.top += rect.bottom / 10;
			rect.bottom -= rect.top;

			SelectObject(hdc, GetStockObject(NULL_BRUSH));
			SelectObject(hdc, CreatePen(PS_DASH, 0, 0));
			Rectangle(hdc, rect.left, rect.top, rect.right,rect.bottom);
			DeleteObject(SelectObject(hdc,GetStockObject(BLACK_PEN)));

			EndPaint(hwnd, &ps);
			return 0;
		
		}
		return DefWindowProc(hwnd, message, wParam, lParam);
	}

}[code]

[freddie1]

idFocus = y<< 8 | x;

idFocus is the result of shifting whatever is in y leftward 8 bits and or'ing this later quantity against whatever is in x.

Using code tags would help. That syntax isn't unique to C.

[ForRealzZzZ]

Thanks there was no explanation in the book about this and the future examples were the same so i was left scratching my head.

So when you use the << operator your really pushing bits to encompass the stuff on the right side. So in essence its the same as allocating memory for a value or a string in assembly?

[freddie1]

I don't know if I'd put it that way. Do a search on C Bitwise Shift Operators or C Shift Operators and that will explain it if you aren't familiar with it. I havn't done assembly in ages, but if I recall correctly there were SHL and SHR or something like that for shifting bits around. They just move them about within a variable. If there isn't room the one's on the left or right edge just disappear or rotate around to the other side. But in your example, I see x and y are ints, so they've got 32 bits. So whatever the bits are they all get shifted left 8 bits. Then x, which may be functioning as a bit mask, gets or'ed against whatever is now in y. idFocus gets the result of those manipulations. I'm not familiar with that Petzold example, but he was a master at those kinds of things!