SDL_Surface question

In my SDL program, I delcare some surfaces at the beginning: SDL_Surface *background = NULL; SDL_Surface *foo = NULL; SDL_Surface *screen = NULL; Then later, I have a fuction that puts images on these surfaces:

bool load_files()
{
    //Load the background image
    background = load_image( "background.png" );

    //If the background didn't load
    if( background == NULL )
    {
        return false;
    }

    //Load the stick figure
    foo = load_image( "foo.png" );

    //If the stick figure didn't load
    if( foo == NULL )
    {
        return false;
    }

    return true;
}

Right now, I'm in the processes of rewriting the above function so I don't have to do an if statment for each and every statement.

bool load_files2(std::string filename, "SDL_Surface as parameter here")
{
    //Load the background image
    "SDL_Surface here" = load_image( filename );

    //If the background didn't load
    if( background == NULL )
    {
        return false;
    }

    return true;
}

My problem is this, how can I declare that the second parameter will be an SDL_Surface?