C语言写代码实验要求： 1.先序遍历创建二叉树； 2.中序线索化二叉树； 3.分别通过 找前驱 和 找后继 的方式，遍历中序线索二叉树。

好的，以下是C语言的代码实现。

1. 先序遍历创建二叉树

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

typedef struct node {
    char data;
    struct node *left;
    struct node *right;
} Node;

Node *create_tree() {
    char ch;
    scanf("%c", &ch);
    if (ch == '#') {
        return NULL;
    }
    Node *root = (Node *) malloc(sizeof(Node));
    root->data = ch;
    root->left = create_tree();
    root->right = create_tree();
    return root;
}

void pre_order_traversal(Node *root) {
    if (root == NULL) {
        return;
    }
    printf("%c ", root->data);
    pre_order_traversal(root->left);
    pre_order_traversal(root->right);
}

int main() {
    printf("请输入先序遍历的字符序列：\n");
    Node *root = create_tree();
    printf("先序遍历结果：\n");
    pre_order_traversal(root);
    return 0;
}

2. 中序线索化二叉树

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

typedef struct node {
    char data;
    struct node *left;
    struct node *right;
    int ltag; // 左线索标记
    int rtag; // 右线索标记
} Node;

Node *create_tree() {
    char ch;
    scanf("%c", &ch);
    if (ch == '#') {
        return NULL;
    }
    Node *root = (Node *) malloc(sizeof(Node));
    root->data = ch;
    root->left = create_tree();
    root->right = create_tree();
    root->ltag = 0;
    root->rtag = 0;
    return root;
}

Node *pre_node(Node *p) {
    Node *q = p->left;
    while (q->rtag == 0) {
        q = q->right;
    }
    return q;
}

Node *next_node(Node *p) {
    Node *q = p->right;
    if (p->rtag == 0) {
        return pre_node(q);
    }
    return q;
}

void in_threading(Node *p, Node **pre) {
    if (p == NULL) {
        return;
    }
    in_threading(p->left, pre);
    if (p->left == NULL) {
        p->ltag = 1;
        p->left = *pre;
    }
    if (*pre != NULL && (*pre)->right == NULL) {
        (*pre)->rtag = 1;
        (*pre)->right = p;
    }
    *pre = p;
    in_threading(p->right, pre);
}

void in_order_traversal(Node *root) {
    Node *p = root;
    while (p->ltag == 0) {
        p = p->left;
    }
    while (p != NULL) {
        printf("%c ", p->data);
        p = next_node(p);
    }
}

int main() {
    printf("请输入先序遍历的字符序列：\n");
    Node *root = create_tree();
    Node *pre = NULL;
    in_threading(root, &pre);
    printf("中序遍历结果：\n");
    in_order_traversal(root);
    return 0;
}

3. 找前驱和找后继的方式遍历中序线索二叉树

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

typedef struct node {
    char data;
    struct node *left;
    struct node *right;
    int ltag; // 左线索标记
    int rtag; // 右线索标记
} Node;

Node *create_tree() {
    char ch;
    scanf("%c", &ch);
    if (ch == '#') {
        return NULL;
    }
    Node *root = (Node *) malloc(sizeof(Node));
    root->data = ch;
    root->left = create_tree();
    root->right = create_tree();
    root->ltag = 0;
    root->rtag = 0;
    return root;
}

Node *pre_node(Node *p) {
    Node *q = p->left;
    while (q->rtag == 0) {
        q = q->right;
    }
    return q;
}

Node *next_node(Node *p) {
    Node *q = p->right;
    if (p->rtag == 0) {
        return pre_node(q);
    }
    return q;
}

void in_threading(Node *p, Node **pre) {
    if (p == NULL) {
        return;
    }
    in_threading(p->left, pre);
    if (p->left == NULL) {
        p->ltag = 1;
        p->left = *pre;
    }
    if (*pre != NULL && (*pre)->right == NULL) {
        (*pre)->rtag = 1;
        (*pre)->right = p;
    }
    *pre = p;
    in_threading(p->right, pre);
}

void in_order_traversal(Node *root) {
    Node *p = root;
    while (p->ltag == 0) {
        p = p->left;
    }
    while (p != NULL) {
        printf("%c ", p->data);
        p = next_node(p);
    }
}

void pre_order_traversal(Node *root) {
    if (root == NULL) {
        return;
    }
    printf("%c ", root->data);
    if (root->ltag == 0) {
        pre_order_traversal(root->left);
    }
    if (root->rtag == 0) {
        pre_order_traversal(root->right);
    }
}

int main() {
    printf("请输入先序遍历的字符序列：\n");
    Node *root = create_tree();
    Node *pre = NULL;
    in_threading(root, &pre);
    printf("中序遍历结果：\n");
    in_order_traversal(root);
    printf("\n先序遍历结果：\n");
    pre_order_traversal(root);
    return 0;
}