A trail in my game...

Here is my pong game or the beginning of it anyway. I know my collision detection stuff doesn't work right and I will fix that later. But when I run this I get a trail behind pongBall. Can someone tell me how to stop this?

Code:

---

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include "SDL.h"
#include <iostream>
using namespace std;
////////////////////////Variables/////////////////
SDL_Surface *screen;
SDL_Surface *ball;
SDL_Surface *lside;
SDL_Surface *rside;
SDL_Surface *uside;
SDL_Surface *dside;

SDL_Rect ballrect;
SDL_Rect lsiderect;
SDL_Rect rsiderect;
SDL_Rect usiderect;
SDL_Rect dsiderect;


int lsidex=0,lsidey=0;
int rsidex=499,rsidey=0;
int usidex=0,usidey=0;
int dsidex=0,dsidey=499;
/////////////////////Classes//////////////////////
class Ball{
    public:
        int xpos;
        int ypos;
        int vely;
        int velx;
        Ball(){xpos=250;ypos=250;velx=-1;vely=1;};
       
};   
Ball pongBall;
//////////////////////Function Declarations////////////////
int LoadScreens();
int redrawscreen();
int loadrects();
int moveball();
int collisiond();


////////////////////////////Main//////////////////// 
int main(int argc, char*argv[])
{
  int done=0;
 
  Ball pongBall;
  LoadScreens();
   
  while(done == 0){
  collisiond();
  moveball(); 
  loadrects();
  redrawscreen();

    SDL_Event event;

    while ( SDL_PollEvent(&event) )
    {
      if ( event.type == SDL_QUIT )  {  done = 1;  }

      if ( event.type == SDL_KEYDOWN )
      {
        if ( event.key.keysym.sym == SDLK_ESCAPE ) { done = 1; }
      }
    }
}   

  return 0;
}

/////////////////////Functions////////////////////

int moveball(){
    pongBall.xpos=pongBall.velx+pongBall.xpos;
    pongBall.ypos=pongBall.vely+pongBall.ypos;
};   

int collisiond(){
    if (pongBall.xpos==0 || pongBall.xpos==499){pongBall.velx=pongBall.velx*-1;};
    if (pongBall.ypos==0 || pongBall.ypos==499){pongBall.vely=pongBall.vely*-1;};   
};   

int LoadScreens(){
    screen= SDL_SetVideoMode(500,500,32,SDL_HWSURFACE||SDL_DOUBLEBUF);
    ball = SDL_LoadBMP("Pic1.bmp");
    lside = SDL_LoadBMP("larside.bmp");
    rside = SDL_LoadBMP("larside.bmp");
    uside = SDL_LoadBMP("UpaDwnside.bmp");
    dside = SDL_LoadBMP("UpaDwnside.bmp");
};

int redrawscreen(){
    SDL_BlitSurface(ball,NULL,screen,&ballrect);
    SDL_BlitSurface(lside,NULL,screen,&lsiderect);
    SDL_BlitSurface(rside,NULL,screen,&rsiderect);
    SDL_BlitSurface(uside,NULL,screen,&usiderect);
    SDL_BlitSurface(dside,NULL,screen,&dsiderect);
    SDL_Flip(screen); 
};

int loadrects(){
    ballrect.x = pongBall.xpos;
    ballrect.y = pongBall.ypos;
    lsiderect.x=lsidex;
    lsiderect.y=lsidey;
    rsiderect.x=rsidex;
    rsiderect.y=rsidey;
    usiderect.x=usidex;
    usiderect.y=usidey;
    dsiderect.x=dsidex;
    dsiderect.y=dsidey;
};

---

I don't know if your stuck on SDL or not but maybe you should check out allegro I have used both and I like allegro better.
http://www.loomsoft.net/resources/al...ltut_index.htm is a the tutorial I learned the basics from its very similar to SDL so you should have no problem switching over. Im not sure what compiler you use but http://www.allegro.cc/ is a good site with details on setting it up with dev or msvc(if you use linux im sure your good enough to figure it out yourself :))

Actually I am stuck on SDL because It is what I have been studying and I hope to move on to 3D some time in the future.

So does anyone know how to get the trail to stop?

Sounds like you are not erasing the old image of the ball. Double buffering should take care of the problem.

Indeed. You can erase the whole screen and redraw everything, or you can erase the ball and redraw it elsewhere - but if you do either of these, then you'll get flickering, which is solved by using the technique of Double-Buffering.