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SDL - Refreshing the screen

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I'm having problems with SDL and trying to refresh the screen. When I run the code below, the ship just moves across the screen, and leaves a trail.
#include "SDL.h"

const int WINDOW_WIDTH = 640;
const int WINDOW_HEIGHT = 480;
const char* WINDOW_TITLE = "SDL Sprites";

int main(int argc, char **argv)
{
   SDL_Init( SDL_INIT_VIDEO );
   
   SDL_Surface* screen = SDL_SetVideoMode( WINDOW_WIDTH, WINDOW_HEIGHT, 0, 
                     SDL_HWSURFACE | SDL_DOUBLEBUF );
   
   SDL_WM_SetCaption( WINDOW_TITLE, 0 ); 
   
   SDL_Surface* ship = SDL_LoadBMP("ship.bmp");
   
   SDL_Rect shipPos;
   shipPos.x = 100;
   shipPos.y = 100;
   shipPos.w = 30;
   shipPos.h = 55;
   
   SDL_SetColorKey(screen, SDL_SRCCOLORKEY, SDL_MapRGB(screen->format, 0, 0, 0));
   
   SDL_Event event;
   
   bool gameRunning = true;
   
   while (gameRunning)
   {
         if (SDL_PollEvent(&event))
         {
            if (event.type == SDL_QUIT)
            {
               gameRunning = false;
            }
         }
         SDL_BlitSurface(ship, NULL, screen, &shipPos);
         
         if (shipPos.x < 610)
         {
            shipPos.x += 1;
         }
         SDL_Flip(screen);
      
         SDL_UpdateRect(screen, 0, 0, 0, 0);
   }
   SDL_FreeSurface(ship);

   SDL_Quit();

   return 0;
}

I've tried putting the line: SDL_UpdateRect(screen, 0, 0, 0, 0); in lines in the while loop, but it still has no effect.

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Clear the screen by filling it white using SDL_FillRect().

Also SDL_Flip() and SDL_UpdateRect() do the same thing in your code so there's no need to call them both.

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