C语言写出非递归算法中序遍历二叉树

以下是C语言非递归算法中序遍历二叉树的实现：

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

// 二叉树节点结构体
struct TreeNode {
    int val;
    struct TreeNode *left;
    struct TreeNode *right;
};

// 栈节点结构体
struct StackNode {
    struct TreeNode *node;
    struct StackNode *next;
};

// 栈结构体
struct Stack {
    struct StackNode *top;
};

// 初始化栈
void initStack(struct Stack *stack) {
    stack->top = NULL;
}

// 入栈
void push(struct Stack *stack, struct TreeNode *node) {
    struct StackNode *newNode = (struct StackNode*)malloc(sizeof(struct StackNode));
    newNode->node = node;
    newNode->next = stack->top;
    stack->top = newNode;
}

// 出栈
struct TreeNode* pop(struct Stack *stack) {
    if (stack->top == NULL) {
        return NULL;
    }
    struct StackNode *temp = stack->top;
    struct TreeNode *node = temp->node;
    stack->top = temp->next;
    free(temp);
    return node;
}

// 中序遍历二叉树
void inorderTraversal(struct TreeNode* root) {
    if (root == NULL) {
        return;
    }
    struct Stack stack;
    initStack(&stack);
    struct TreeNode *node = root;
    while (node != NULL || stack.top != NULL) {
        while (node != NULL) {
            push(&stack, node);
            node = node->left;
        }
        node = pop(&stack);
        printf("%d ", node->val);
        node = node->right;
    }
}

// 测试
int main() {
    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;
    inorderTraversal(root); // 输出：2 1 4 3 5
    return 0;
}