usage of memset

[APTXASZC]

void remove_line()
{
  for (int row = y; row <= y + NUM(r, 18); row++)
  {
    c = 1;
    for (int i = 0; i < 10; i++)
    {
      c *= board[row][i];
    }
    if (!c)
    {
      continue;
    }
    for (int i = row - 1; i > 0; i--) 
    {
      memcpy(&board[i + 1][0], &board[i][0], 40);
    }
    memset(&board[0][0], 0, 10);  // **# I feel like it should be 40**
    score++;
  }
}