SDL scrolling

//http://www.youtube.com/user/thecplusplusguy
//you need a chessimage.bmp 1920*1920 image
#include <SDL/SDL.h>
#include <iostream>

int main(int argc,char** argv)
{
    SDL_Init(SDL_INIT_EVERYTHING);
    SDL_Surface* screen=SDL_SetVideoMode(640,480,32,SDL_SWSURFACE);
    bool running=true;
    Uint32 start;
    SDL_Event event;
    bool b[4]={0,0,0,0};
    SDL_Surface* chessImage=SDL_LoadBMP("chessimage.bmp");
    if(!chessImage)
        std::cout << "You don't ave chessimage.bmp" << std::endl;
    SDL_Rect camera={0,0,640,480};
    SDL_Rect playerpos={320,240,20,20};
    while(running)
    {
        start=SDL_GetTicks();
        while(SDL_PollEvent(&event))
        {
            switch(event.type)
            {
                case SDL_QUIT:
                    running=false;
                    break;
                case SDL_KEYDOWN:
                    switch(event.key.keysym.sym)
                    {
                        case SDLK_ESCAPE:
                            running=false;
                            break;
                        case SDLK_UP:
                            b[0]=true;
                            break;
                        case SDLK_RIGHT:
                            b[1]=true;
                            break;
                        case SDLK_DOWN:
                            b[2]=true;
                            break;
                        case SDLK_LEFT:
                            b[3]=true;
                            break;
                    }
                    break;
                case SDL_KEYUP:
                    switch(event.key.keysym.sym)
                    {
                        case SDLK_ESCAPE:
                            running=false;
                            break;
                        case SDLK_UP:
                            b[0]=false;
                            break;
                        case SDLK_RIGHT:
                            b[1]=false;
                            break;
                        case SDLK_DOWN:
                            b[2]=false;
                            break;
                        case SDLK_LEFT:
                            b[3]=false;
                            break;
                    }
                    break;
            }
        }
        if(b[0])
        {
            if(playerpos.y>=30)
                playerpos.y-=3;
            else
                camera.y-=3;
        }
        if(b[1])
        {
            if(playerpos.x<=610)
                playerpos.x+=3;
            else
                camera.x+=3;
        }
        if(b[2])
        {
            if(playerpos.x<=450)
                playerpos.y+=3;
            else
                camera.y+=3;
        }
        if(b[3])
        {
            if(playerpos.x>=30)
                playerpos.x-=3;
            else
                camera.x-=3;
        }
        if(camera.x>1920-640)   //image width: 1920, screen-width: 640
            camera.x=0;
        if(camera.y>1920-480)
            camera.y=0;
        if(camera.x<0)
            camera.x=1920-640;
        if(camera.y<0)
            camera.y=1920-640;

        SDL_BlitSurface(chessImage,&camera,screen,NULL);
        SDL_FillRect(screen,&playerpos,SDL_MapRGB(screen->format,255,0,0));
        SDL_Flip(screen);
        if(1000/30>(SDL_GetTicks()-start))
            SDL_Delay(1000/30-(SDL_GetTicks()-start));
    }
    SDL_Quit();
    return 0;
}