C++, SDL, function doesnt seem to change main surface after first launch - c++

Question

Here is the code of draw()
My problem is that it draws things only once, then it draws the same.
I am using SLD_Flip(surface) after it.
sqrbmp, applebmp, blank are surfaces with BMP loaded
des is a rectangle
screen is main surface
It is supposed to draw a game map.
Where is my bad?
// includes, defines etc.
const int mapx = 32; // 640 / 20(bmp size)
const int mapy = 24; // 480 / 20
//nothing important
SDL_Event keys;
SDL_Surface * screen = NULL;
SDL_Surface * blank = NULL;
SDL_Surface * sqrbmp = NULL;
SDL_Surface * applebmp = NULL;
SDL_Rect des;
int map[mapy][mapx];
// nothing important
// nothing important
struct square
{
square(int xt, int yt, int dirt);
int x;
int y;
int dir;
};
std::vector <square> snake;
square::square(int xt, int yt, int dirt)
{
x = xt;
y = yt;
dir = dirt;
snake.push_back(*this);
}
bool squareontile(int x, int y)
{
// returns true if there is square on that tile
}
void draw()
{
for(int yt = 0 ; yt < mapy; yt++)
{
for(int xt = 0 ; xt < mapx; xt++)
{
des.y = yt * 20;
des.x = xt * 20;
if(squareontile(xt,yt) == 1)
{
SDL_BlitSurface(sqrbmp, NULL, screen, &des);
}
else
{
switch(map[yt][xt])
{
case 5:
SDL_BlitSurface(applebmp, NULL, screen, &des);
break;
default:
SDL_BlitSurface(blank, NULL, screen, &des);
break;
}
}
}
}
}
// nothing important
void checkmap()
{
for(int yt = 0 ; yt < mapy; yt++)
{
for(int xt = 0 ; xt < mapx; xt++)
{
if(squareontile(xt,yt) == 0 && map[yt][xt] != 5)
{
map[yt][xt] = 0;
}
}
}
}
bool checksnake()
{
for(int a = 0; a < snake.size() ; a++)
{
for(int b = 0; b < snake.size() ; b++)
{
if(snake[a].y == snake[b].y && snake[a].x == snake[b].x && a != b)
{
return true;
}
}
}
}
// nothing important
void apple()
{
if(!appleisonmap())
{
int y;
int x;
do
{
y = rand() % mapy;
x = rand() % mapx;
} while(squareontile(x,y));
map[y][x] = 5;
}
}
// nothing important
int main( int argc, char * args[] )
{
// nothing important
SDL_Init( SDL_INIT_EVERYTHING );
screen = SDL_SetVideoMode( 640, 480, 24, SDL_SWSURFACE );
applebmp = SDL_LoadBMP("apple.bmp"); // 20x20
blank = SDL_LoadBMP("blank.bmp"); // 20x20
sqrbmp = SDL_LoadBMP( "sqr.bmp" ); // 20x20
for(int b = 7 ; b > 0 ; b--)
{
square(5,b,1);
}
while(!exitv && !game_over)
{
draw();
game_over = checksnake();
SDL_Flip( screen );
SDL_Delay(100);
while( SDL_PollEvent( & keys ) )
{
if( keys.type == SDL_QUIT )
{
exitv = true;
}
// detecting other keys, input for moving, ya know
}
checkmap();
apple();
checksquare();
}
SDL_FreeSurface( sqrbmp );
SDL_FreeSurface( applebmp );
SDL_FreeSurface( blank );
SDL_Quit();
return 0;
}

Answer 1

Ahh found the error. I just forgot 1 function and the snake wasnt moving.