sidescroller collision 2

//better collision?
    int dirX=(xvel>0 ? 1 : (xvel<0 ? -1 : 0));  //move pixel by pixel through multiple iteration
    int dirY=(yvel>0 ? 1 : (yvel<0 ? -1 : 0));
    int a=10;   //a margin of the pixel, basically the border-width.
    int speedX=xvel;
    int speedY=yvel;
    for(int j=0;j<abs(yvel) || j<abs(xvel);j++) //this is done, so when the character goes fast, it doesn't move into the wall (move pixel by picel)
    {
        if(speedX)      //if we still need to move on the x, move
        {
            box.x+=dirX;
            speedX-=dirX;
        }
        if(speedY)  //same with y
        {
            box.y+=dirY;
            speedY-=dirY;
    }
          for(int i = 0; i < map.size(); i++){
              for(int j = start; j < end; j++){
                  if(map[i][j] == 0){
                      continue;
                  }
                  SDL_Rect destrect = {j * 50, i * 50, 50, 50};
                  int err=0;
                  if(collision(&box,&destrect)){
                      noCollision = false;


                      //create the 4 inside rect
                      SDL_Rect top={box.x,box.y,box.w,a};
                      SDL_Rect bottom={box.x,box.y+box.h-a,box.w,a};
                      SDL_Rect left={box.x,box.y+a,a,box.h-2*a};
                      SDL_Rect right={box.x+box.w-a,box.y+a,a,box.h-2*a};
                      SDL_Rect center={box.x+a,box.y+a,box.w-2*a,box.h-2*a};

                      //do the right back movement, if we have collision on the left
                      if(collision(&destrect,&left))
                      {
                        box.x++;
                        setDirection();
                      }else if(collision(&destrect,&right)) //right...
                      {
                        box.x--;
                        setDirection();
                      }
                      else if(collision(&destrect,&top))
                      {
                        box.y++;
                      }
                      else if(collision(&destrect,&bottom))
                      {
                        box.y--;
                        ground=true;
                      }
                      if(collision(&destrect,&center))  //we shouldn't get here, there is a block inside the player, try to move out
                      {
                        box.x--;
                        box.y--;
                      }
               }
            }
        }
    }