程序代码：

#include <stdio.h>
#include <stdlib.h>

typedef struct node
{
    int data;
    struct node *l_child;
    struct node *r_child;
}*BTree;

BTree create(BTree tree)
{
    int temp;
    scanf("%d", &temp);

    if (temp == 0)
    {
        tree = NULL;
    }
    else
    {
        tree = (BTree) malloc (sizeof(struct node));

        tree->l_child = create(tree->l_child);
        tree->r_child = create(tree->r_child);
    }

    return tree;
}

BTree init(BTree tree)
{
    if ( tree != NULL )
    {
        tree->l_child = init(tree->l_child);
        scanf("%d", &tree->data);
        tree->r_child =    init(tree->r_child);
    }

    return tree;
}

void show(BTree tree)
{
    if (tree != NULL)
    {
        show(tree->l_child);
        printf("%d ", tree->data);
        show(tree->r_child);
    }
}

int main(void)
{
    BTree tree = NULL;

    tree = create(tree);
    printf("\n");

    tree = init(tree);

    show(tree);
    printf("\n");

    return 0;
}