problem with loops

here is the code:

Code:

---

/* this is a member of "map" which has:
    string name;
    int ref_num;
    int w, h;
    tileset tiles;
    int tileset_ref;
    vector< vector<int> > data;

    tileset has:
    string name;
    int ref_num;
    vector<SDL_Surface*> tile;

    SDL_Surface is the thing that SDL uses or the screen and images
*/
    void view( int x, int y ){
        if( x > w || y > h ) return;    //if x is larger than the width of the map or y the height, something is wrong
        int i, j, tempx;
        fillrect( screen, 0, 0, screen->w, screen->h, black ); //clear the screen

        tempx = x;
//notice that data has data stored like this: data[up and down][side to side]
        for( i = 0; i != screen->h/32; i++ ){
            for( j = 0; j != screen->w/32; j++ ){
                DisplayImage( screen, tiles.tile[ data[y][x] ], j * TILE_W, i * TILE_H );
//DisplayImage( SDL_Surface *dest, SDL_Surface *image, x, y ) x, y of the top left corner
                if( x == w ) break;
                x++;
            }
            if( y == h ) break;
            x = tempx;
            y++;
        }
        SDL_UpdateRect( screen, 0, 0, 0, 0 );  //update the whole screen (double buffering)     
    }

---

the line "DisplayImage( screen, tiles.tile[ data[y][x] ], j * TILE_W, i * TILE_H );" is segfaulting when the loop within the larger is on its second round. data[y][x] is he same value both the first and second times.