动态设置窗口全屏却成窗口风格，设置回窗口却变成全屏，不明白

窗口风格究竟怎么了，要反着来吗?
谁写过类似代码，以下代码符合要求，只是代码对调写了。
int boolFullScreen=0;
#define windowStyle WS_SYSMENU|WS_MINIMIZEBOX|WS_MAXIMIZEBOX/*窗口模式风格*/
#define fullScreenStyle WS_POPUPWINDOW/*全屏风格*/
case WM_LBUTTONDBLCLK:/*双击*/
if(!boolFullScreen){
tmp=GetWindowLong(hwnd,GWL_STYLE);
tmp &=~fullScreenStyle;
tmp |=windowStyle;
SetWindowLong(hwnd,GWL_STYLE,tmp);/*设置全屏却用窗口风格*/
MoveWindow(hwnd,0,0,wScreen,hScreen,0);
boolFullScreen|=1;
}
case VK_ESCAPE:/**/
if(boolFullScreen){/*全屏才退出*/
tmp=GetWindowLong(hwnd,GWL_STYLE);
tmp &=~windowStyle;
tmp |=fullScreenStyle;/*倒着用了*/
SetWindowLong(hwnd,GWL_STYLE,tmp);/*窗口的风格却用全屏风格*/
MoveWindow(hwnd,xWind,yWind,wWind,hWind,0);
boolFullScreen&=0;}