Thread: What is wrong with this C++ SDL code?

I'm new to programming and I've spent some time learning the basics of c++ and the basics of SDL. I've started to work on a little project of a 2d game engine. My goal is to make a 24x16 tiles room and adding a controllable animated character for the player to move around with.

I started writing the code for genereting the level itself. When I compile and run it I get no errors, but the screen stays black, without showing any of the tiles. Can somebody tell me what is wrong?

Code:

#include "SDL.h"
#include "SDL_image.h"


const int SCREEN_WIDTH = 384;
const int SCREEN_HEIGHT = 256;
const int SCREEN_BPP = 16;


const int TILE_WIDTH = 16;
const int TILE_HEIGHT = 16;
const int TILES_NUMBER = 384;
const int TILE_SPRITES = 4;
const int TILE_WALL = 0;
const int TILE_EDGE = 1;
const int TILE_ROCKS = 2;
const int TILE_PLATFORM = 3;


SDL_Rect clipTiles[4];

int main( int argc, char* args[] )
{
    SDL_Init( SDL_INIT_EVERYTHING );
    screen = SDL_SetVideoMode( SCREEN_WIDTH, SCREEN_HEIGHT, SCREEN_BPP, SDL_SWSURFACE );
    tiles = IMG_Load( "tiles.png" );


    int x = NULL;
    int map[ 384 ] = {0, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 0,
                      0, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 0,
                      0, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 0,
                      0, 2, 2, 0, 0, 0, 0, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 0, 0, 0, 0, 2, 2, 0,
                      0, 2, 2, 0, 0, 0, 0, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 0, 0, 0, 0, 2, 2, 0,
                      0, 2, 2, 1, 1, 1, 1, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 1, 1, 1, 1, 2, 2, 0,
                      0, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 0,
                      0, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 0,
                      0, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 0,
                      0, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 0,
                      0, 2, 2, 0, 0, 0, 0, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 0, 0, 0, 0, 2, 2, 0,
                      0, 2, 2, 0, 0, 0, 0, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 0, 0, 0, 0, 2, 2, 0,
                      0, 2, 2, 1, 1, 1, 1, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 1, 1, 1, 1, 2, 2, 0,
                      0, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 0,
                      0, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 0,
                      0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0};
    x = 0;
    for( int x = 0; x > 4; x++);
    {
        clipTiles[ x ].x = x * 16;
        clipTiles[ x ].y = 0;
        clipTiles[ x ].h = 16;
        clipTiles[ x ].w = 16;
    }
    x = 0;
    for( x = 0; x > 384; x++)
    {
        SDL_Rect offset;
        offset.x = (x)*16;
        offset.y = x/16;
        SDL_BlitSurface( tiles, &clipTiles[ map[ x ] ], screen, &offset );
    }


    SDL_Flip( screen );


    SDL_Delay (2000);


    return 0;
}

This is what I've done so far. I added the delay just to be able to see if the program was working. As you can see the character is not yet implemented into the game, and some of the variables are not yet being used.

The tiles.png is a simple sprite sheet with 4 16x16 tiles drawn in a horisontal line after each other.

EDIT: I just noticed that I set the variable x = 0 a little too many times. Sorry for that, but as far as I'm concerned it should have no effect on the program itself.

There's actually quite a bit going on. Here's my synopsis:

1)SDL_Image needs to be initialised just as SDL does, with a call to IMG_Init.

2)Keep in mind that in a for loop, for(a;b;c) loops until b is false, or likewise, as long as b is true.

2.5)

Code:

    for( int x = 0; x > 4; x++);
    {
        clipTiles[ x ].x = x * 16;
        clipTiles[ x ].y = 0;
        clipTiles[ x ].h = 16;
        clipTiles[ x ].w = 16;
    }

Stray semicolon here; also, you declared another variable 'x' local to the for loop. I don't know if it was intentional and it doesn't affect anything in this case but I'd suggest you try to be as consistent as possible w/regard to this to avoid confusion.

3)

Code:

        offset.x = (x)*16;
        offset.y = x/16;

My guess is that since you have parentheses around x, you meant to do more here and never got back to it (hint hint ) You probably would have got here eventually once the rest of the program was fixed. EDIT: Yep you got it.