some asking in c++

[iammfa]

Hi,
Here is an example made by 'C++' and 'SDL' library, this example load an image with format .PNG, because I'm beginner in c++, I'm asking some questions:

/*This source code copyrighted by Lazy Foo' Productions (2004-2009) and may not
be redestributed without written permission.*/

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

//Screen attributes
const int SCREEN_WIDTH = 640;
const int SCREEN_HEIGHT = 480;
const int SCREEN_BPP = 32;

//The surfaces
SDL_Surface *image = NULL;
SDL_Surface *screen = NULL;

SDL_Surface *load_image( std::string filename )
{
    //The image that's loaded
    SDL_Surface* loadedImage = NULL;

    //The optimized image that will be used
    SDL_Surface* optimizedImage = NULL;

    //Load the image using SDL_image
    loadedImage = IMG_Load( filename.c_str() );

    //If the image loaded
    if( loadedImage != NULL )
    {
        //Create an optimized image
        optimizedImage = SDL_DisplayFormat( loadedImage );

        //Free the old image
        SDL_FreeSurface( loadedImage );
    }

    //Return the optimized image
    return optimizedImage;
}

void apply_surface( int x, int y, SDL_Surface* source, SDL_Surface* destination )
{
    //Rectangle to hold the offsets
    SDL_Rect offset;

    //Get offsets
    offset.x = x;
    offset.y = y;

    //Blit the surface
    SDL_BlitSurface( source, NULL, destination, &offset );
}

bool init()
{
    //Initialize all SDL subsystems
    if( SDL_Init( SDL_INIT_EVERYTHING ) == -1 )
    {
        return false;
    }

    //Set up the screen
    screen = SDL_SetVideoMode( SCREEN_WIDTH, SCREEN_HEIGHT, SCREEN_BPP, SDL_SWSURFACE );

    //If there was an error in setting up the screen
    if( screen == NULL )
    {
        return false;
    }

    //Set the window caption
    SDL_WM_SetCaption( "PNG test", NULL );

    //If everything initialized fine
    return true;
}

void clean_up()
{
    //Free the surface
    SDL_FreeSurface( image );

    //Quit SDL
    SDL_Quit();
}

int main( int argc, char* args[] )
{
    //Initialize
    if( init() == false )
    {
        return 1;
    }

    //Load the image
    image = load_image( "look.png" );

    //If there was a problem in loading the image
    if( image == NULL )
    {
        return 1;
    }

    //Apply the surface to the screen
    apply_surface( 0, 0, image, screen );

    //Update the screen
    if( SDL_Flip( screen ) == -1 )
    {
        return 1;
    }

    //Wait 2 seconds
    SDL_Delay( 2000 );

    //Free the surface and quit SDL
    clean_up();

    return 0;
}

Question 01:

SDL_Surface *image = NULL;

SDL_Surface* loadedImage = NULL;

I know well it use a pointers but what is the difference between two lines, the first line the star operator beside image and the second line the star beside Surface

Question 02:

SDL_BlitSurface( source, NULL, destination, &offset );

why we use this operator &offset

Question 03:

int main( int argc, char* args[] )

I know well it must use int main function as typed, but what is the meaning of these parameters int argc, char* args[]

[Ketsuekiame]

Question 1: Absolutely nothing. Just pick a convention and stick to it.
Question 2: Check the documentation. It will tell you what offset is used for. Probably to offset something...
Question 3: argc is the number of command line arguments received. char* args[] is a pointer to an array of characters (which represent the arguments)

It is also often shown as char** argv which is a pointer to a pointer of characters.