使用C语言写一段二叉树的遍历代码

以下是二叉树的前序遍历、中序遍历和后序遍历的 C 语言代码实现：

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

// 二叉树结点定义
typedef struct TreeNode {
    int val;
    struct TreeNode* left;
    struct TreeNode* right;
} TreeNode;

// 前序遍历二叉树
void preorderTraversal(TreeNode* root) {
    if (root == NULL) {
        return;
    }
    printf("%d ", root->val);  // 访问当前结点
    preorderTraversal(root->left);  // 遍历左子树
    preorderTraversal(root->right);  // 遍历右子树
}

// 中序遍历二叉树
void inorderTraversal(TreeNode* root) {
    if (root == NULL) {
        return;
    }
    inorderTraversal(root->left);  // 遍历左子树
    printf("%d ", root->val);  // 访问当前结点
    inorderTraversal(root->right);  // 遍历右子树
}

// 后序遍历二叉树
void postorderTraversal(TreeNode* root) {
    if (root == NULL) {
        return;
    }
    postorderTraversal(root->left);  // 遍历左子树
    postorderTraversal(root->right);  // 遍历右子树
    printf("%d ", root->val);  // 访问当前结点
}

int main() {
    // 创建二叉树
    TreeNode* root = (TreeNode*)malloc(sizeof(TreeNode));
    root->val = 1;

    root->left = (TreeNode*)malloc(sizeof(TreeNode));
    root->left->val = 2;
    root->left->left = NULL;
    root->left->right = NULL;

    root->right = (TreeNode*)malloc(sizeof(TreeNode));
    root->right->val = 3;

    root->right->left = (TreeNode*)malloc(sizeof(TreeNode));
    root->right->left->val = 4;
    root->right->left->left = NULL;
    root->right->left->right = NULL;

    root->right->right = (TreeNode*)malloc(sizeof(TreeNode));
    root->right->right->val = 5;
    root->right->right->left = NULL;
    root->right->right->right = NULL;

    // 遍历二叉树
    printf("Preorder traversal: ");
    preorderTraversal(root);
    printf("\n");

    printf("Inorder traversal: ");
    inorderTraversal(root);
    printf("\n");

    printf("Postorder traversal: ");
    postorderTraversal(root);
    printf("\n");

    return 0;
}

运行结果：

Preorder traversal: 1 2 3 4 5
Inorder traversal: 2 1 4 3 5
Postorder traversal: 2 4 5 3 1