C++, "has stopped working"

#include "SDL/SDL.h"
#include "SDL/SDL_image.h"
#include <string>


const int SCREEN_WIDTH = 800;
const int SCREEN_HEIGHT = 600;
const int SCREEN_BPP = 32;

SDL_Surface *co[9] = { NULL };
SDL_Surface *screen = NULL;
SDL_Event event;


SDL_Surface *load_image( std::string filename )
{     
      SDL_Surface* loadedImage = NULL;
      SDL_Surface* optimizedImage = NULL;
      
      loadedImage = IMG_Load( filename.c_str() );
      
      if ( loadedImage != NULL )
      {
           optimizedImage = SDL_DisplayFormat( loadedImage );
           
           SDL_FreeSurface( loadedImage);
      }
      
      return optimizedImage;
}


void apply_surface( int x, int y, SDL_Surface* source, SDL_Surface* destination )
{
     SDL_Rect offset;
     
     offset.x = x;
     offset.y = y;
     
     SDL_BlitSurface( source, NULL, destination, &offset );
}


bool init()
{
     if( SDL_Init(SDL_INIT_EVERYTHING) == -1 )
     {
         return false;
     }
     
     screen = SDL_SetVideoMode( SCREEN_WIDTH, SCREEN_HEIGHT, SCREEN_BPP, SDL_SWSURFACE );
     
     if( screen == NULL )
     {
         return false;
     }
     
     SDL_WM_SetCaption( "TTT", NULL );
     
     return true;
}


bool load_files()
{
     for( int i = 0; i < 9; i++ )
     {
     co[i] = load_image("./images/empty.png");
     }
}


void clean_up()
{
     for( int i = 0; i < 9; i++ )
     {
     SDL_FreeSurface( co[i] );
     }
     
     SDL_Quit();
}



int main( int argc, char* args[] )
{
    bool quit = false;
    
    if( init == false )
    {
        return 1;
    }
    
    if( load_files() == false )
    {
        return 1;
    }
    
    apply_surface( 0, 0, co[0], screen );
    
    if( SDL_Flip( screen ) == -1 )
    {
        return 1;
    }
    
    while( quit == false )
    {
           while( SDL_PollEvent( &event ))
           {
                  if( event.type == SDL_QUIT )
                  {
                      quit = true;
                  }
           }
    }
    
    clean_up();
    
    return 0;
}