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SDL help

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Hello all, I am following the SDL tutorial on Cone3d. I am on the first tutorial. I can get all the way to the part where I add SDL_FULLSCREEN but when i try to add the drawing code, it comes up with 3 errors. I am using Visual Studio.net 2003. Here is the code
#include <stdio.h>
#include <stdlib.h>

#include <SDL/SDL.h>


void DrawPixel(SDL_Surface *screen, int x, int y,
                                    Uint8 R, Uint8 G, Uint8 B);
void Slock(SDL_Surface *screen);
void Sulock(SDL_Surface *screen);


int main(int argc, char *argv[])
{

  if ( SDL_Init(SDL_INIT_AUDIO|SDL_INIT_VIDEO) < 0 )
  {
    printf("Unable to init SDL: %s\n", SDL_GetError());
    exit(1);
  }
  atexit(SDL_Quit);

  SDL_Surface *screen;
  screen=SDL_SetVideoMode(640,480,32,SDL_HWSURFACE|SDL_DOUBLEBUF|SDL_FULLSCREEN);
  if ( screen == NULL )
  {
    printf("Unable to set 640x480 video: %s\n", SDL_GetError());
    exit(1);
  }


  Slock(screen);
  for(int x=0;x<640;x++)
  {
    for(int y=0;y<480;y++)
    {
      DrawPixel(screen, x,y,y/2,y/2,x/3);
    }
  }
  Sulock(screen);
  SDL_Flip(screen);






  return 0;
}

and the error it gets
main.obj : error LNK2019: unresolved external symbol "void __cdecl Sulock(struct SDL_Surface *)" (?Sulock@@YAXPAUSDL_Surface@@@Z) referenced in function _SDL_main
main.obj : error LNK2019: unresolved external symbol "void __cdecl DrawPixel(struct SDL_Surface *,int,int,unsigned char,unsigned char,unsigned char)" (?DrawPixel@@YAXPAUSDL_Surface@@HHEEE@Z) referenced in function _SDL_main
main.obj : error LNK2019: unresolved external symbol "void __cdecl Slock(struct SDL_Surface *)" (?Slock@@YAXPAUSDL_Surface@@@Z) referenced in function _SDL_main
Debug/gp3.exe : fatal error LNK1120: 3 unresolved externals

any help will be appreciated.

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replace this part of your code

void DrawPixel(SDL_Surface *screen, int x, int y,
Uint8 R, Uint8 G, Uint8 B);
void Slock(SDL_Surface *screen);
void Sulock(SDL_Surface *screen);


with this:

void Slock(SDL_Surface *screen)
{
if ( SDL_MUSTLOCK(screen) )
{
if ( SDL_LockSurface(screen) < 0 )
{
return;
}
}
}

void Sulock(SDL_Surface *screen)
{
if ( SDL_MUSTLOCK(screen) )
{
SDL_UnlockSurface(screen);
}
}

void DrawPixel(SDL_Surface *screen, int x, int y,
Uint8 R, Uint8 G, Uint8 B)
{
Uint32 color = SDL_MapRGB(screen->format, R, G, B);
switch (screen->format->BytesPerPixel)
{
case 1: // Assuming 8-bpp
{
Uint8 *bufp;
bufp = (Uint8 *)screen->pixels + y*screen->pitch + x;
*bufp = color;
}
break;
case 2: // Probably 15-bpp or 16-bpp
{
Uint16 *bufp;
bufp = (Uint16 *)screen->pixels + y*screen->pitch/2 + x;
*bufp = color;
}
break;
case 3: // Slow 24-bpp mode, usually not used
{
Uint8 *bufp;
bufp = (Uint8 *)screen->pixels + y*screen->pitch + x * 3;
if(SDL_BYTEORDER == SDL_LIL_ENDIAN)
{
bufp[0] = color;
bufp[1] = color >> 8;
bufp[2] = color >> 16;
} else {
bufp[2] = color;
bufp[1] = color >> 8;
bufp[0] = color >> 16;
}
}
break;
case 4: // Probably 32-bpp
{
Uint32 *bufp;
bufp = (Uint32 *)screen->pixels + y*screen->pitch/4 + x;
*bufp = color;
}
break;
}
}

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