c – 无法释放内存

int LuffarschackStart(void)
{
/* to avoid the program from closing */
char readEnd;
int i = 0;    

board_type *board = malloc(sizeof(square_type));
if (board == NULL)
{
    printf("Could not allocate the memory needed...");
    scanf("%c",&readEnd);         
    return 0;
}

for(i = 0; i < 9; i = i + 1)
    board->square[i].piece_type = NO_PIECE;

board_play_game(board);    

free(board);
printf("Press any key and enter to quit the program...");
scanf("%c",&readEnd);         
return 0;
}

我分配的板结构如下所示：

typedef struct
{
    /* flag to indicate if a square is free or not */  
    int free;
    /* the type of piece stored on the square if the 
       square is not free,in this case the admissible 
       values are CROSS_PIECE and CIRCLE_PIECE,otherwise the value NO_PIECE is used */ 
    int piece_type; 
} square_type; 

typedef struct
{
    square_type square[N_SQUARES]; 
    int computer_type;
    int player_type;
} board_type;

可能问题是我需要首先释放板内的square_type吗？如果是这样的话,我如何解放？