用c语言

好的，以下是使用 C 语言实现二叉树的建立和四种遍历方式的代码：

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

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

// 先序遍历，根左右
void preorder(struct TreeNode* root) {
    if (root == NULL) return;
    printf("%d ", root->val);
    preorder(root->left);
    preorder(root->right);
}

// 中序遍历，左根右
void inorder(struct TreeNode* root) {
    if (root == NULL) return;
    inorder(root->left);
    printf("%d ", root->val);
    inorder(root->right);
}

// 后序遍历，左右根
void postorder(struct TreeNode* root) {
    if (root == NULL) return;
    postorder(root->left);
    postorder(root->right);
    printf("%d ", root->val);
}

// 层次遍历
void levelorder(struct TreeNode* root) {
    if (root == NULL) return;
    struct TreeNode* queue[1000];
    int front = 0, rear = 0;
    queue[rear++] = root;
    while (front != rear) {
        struct TreeNode* cur = queue[front++];
        printf("%d ", cur->val);
        if (cur->left) queue[rear++] = cur->left;
        if (cur->right) queue[rear++] = cur->right;
    }
}

// 建立二叉树
struct TreeNode* buildTree() {
    int val;
    scanf("%d", &val);
    if (val == -1) return NULL;
    struct TreeNode* root = (struct TreeNode*)malloc(sizeof(struct TreeNode));
    root->val = val;
    root->left = buildTree();
    root->right = buildTree();
    return root;
}

int main() {
    printf("请输入二叉树的节点值，-1表示空节点：\n");
    struct TreeNode* root = buildTree();

    printf("先序遍历结果：");
    preorder(root);
    printf("\n");

    printf("中序遍历结果：");
    inorder(root);
    printf("\n");

    printf("后序遍历结果：");
    postorder(root);
    printf("\n");

    printf("层次遍历结果：");
    levelorder(root);
    printf("\n");

    return 0;
}

注意：这里输入的二叉树按照先序遍历的方式输入，-1 表示空节点。可以根据需要进行修改。