用C语言编写一个遍历二叉树

好的，以下是一个用C语言编写的遍历二叉树的示例代码：

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

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

// 先序遍历二叉树
void preorderTraversal(struct TreeNode* root) {
    if (root) {
        printf("%d ", root->val);
        preorderTraversal(root->left);
        preorderTraversal(root->right);
    }
}

// 中序遍历二叉树
void inorderTraversal(struct TreeNode* root) {
    if (root) {
        inorderTraversal(root->left);
        printf("%d ", root->val);
        inorderTraversal(root->right);
    }
}

// 后序遍历二叉树
void postorderTraversal(struct TreeNode* root) {
    if (root) {
        postorderTraversal(root->left);
        postorderTraversal(root->right);
        printf("%d ", root->val);
    }
}

int main() {
    // 构造一个二叉树
    struct TreeNode* root = (struct TreeNode*)malloc(sizeof(struct TreeNode));
    root->val = 1;
    root->left = (struct TreeNode*)malloc(sizeof(struct TreeNode));
    root->left->val = 2;
    root->left->left = NULL;
    root->left->right = NULL;
    root->right = (struct TreeNode*)malloc(sizeof(struct TreeNode));
    root->right->val = 3;
    root->right->left = (struct TreeNode*)malloc(sizeof(struct TreeNode));
    root->right->left->val = 4;
    root->right->left->left = NULL;
    root->right->left->right = NULL;
    root->right->right = (struct TreeNode*)malloc(sizeof(struct TreeNode));
    root->right->right->val = 5;
    root->right->right->left = NULL;
    root->right->right->right = NULL;

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

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

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

    return 0;
}

这里定义了一个二叉树的结构体 `TreeNode`，包含节点值 `val`，左子节点 `left` 和右子节点 `right`。然后定义了三个遍历二叉树的函数：先序遍历 `preorderTraversal`，中序遍历 `inorderTraversal` 和后序遍历 `postorderTraversal`。在 `main` 函数中，构造了一个二叉树，并依次遍历该二叉树。