[C++] Co oznacza kod wyjścia z aplikacji gdy się ona wysypie?

#include <SFML/Window.hpp>

int main()
{
    sf::Window window( sf::VideoMode( 800, 600 ), "My window" );
   
    // run the program as long as the window is open
    while( window.isOpen() )
    {
        // check all the window's events that were triggered since the last iteration of the loop
        sf::Event event;
        while( window.pollEvent( event ) )
        {
            // "close requested" event: we close the window
            if( event.type == sf::Event::Closed )
                 window.close();
           
        }
    }
   
    return 0;
}