SDL_WM_ToggleFullScreen (3) - Linux Manuals
SDL_WM_ToggleFullScreen: Toggles fullscreen mode
NAMESDL_WM_ToggleFullScreen - Toggles fullscreen mode
int SDL_WM_ToggleFullScreen(SDL_Surface *surface);
Toggles the application between windowed and fullscreen mode, if supported. (X11 is the only target currently supported, BeOS support is experimental).
Returns 0 on failure or 1 on success.