树结构用C语言写完整嵌套代码

以下是一个简单的树结构的嵌套代码：

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

struct TreeNode {
    int val;
    struct TreeNode *left;
    struct TreeNode *right;
};

struct TreeNode* createNode(int val) {
    struct TreeNode* node = (struct TreeNode*) malloc(sizeof(struct TreeNode));
    node->val = val;
    node->left = NULL;
    node->right = NULL;
    return node;
}

void insert(struct TreeNode* parent, int val) {
    if (parent->left == NULL) {
        parent->left = createNode(val);
    } else if (parent->right == NULL) {
        parent->right = createNode(val);
    } else {
        printf("Cannot insert %d as parent node already has two children\n", val);
    }
}

void preOrder(struct TreeNode* node) {
    if (node == NULL) {
        return;
    }
    printf("%d ", node->val);
    preOrder(node->left);
    preOrder(node->right);
}

void inOrder(struct TreeNode* node) {
    if (node == NULL) {
        return;
    }
    inOrder(node->left);
    printf("%d ", node->val);
    inOrder(node->right);
}

void postOrder(struct TreeNode* node) {
    if (node == NULL) {
        return;
    }
    postOrder(node->left);
    postOrder(node->right);
    printf("%d ", node->val);
}

int main() {
    struct TreeNode* root = createNode(1);
    insert(root, 2);
    insert(root, 3);
    insert(root->left, 4);
    insert(root->left, 5);
    insert(root->right, 6);
    insert(root->right, 7);

    printf("Pre-order traversal: ");
    preOrder(root);
    printf("\n");

    printf("In-order traversal: ");
    inOrder(root);
    printf("\n");

    printf("Post-order traversal: ");
    postOrder(root);
    printf("\n");

    return 0;
}

这个代码示例实现了一个基本的树结构，包括节点的创建、插入和三种遍历方法（前序、中序和后序遍历）。你可以根据需求修改或扩展该代码。