c 二叉树的非递归遍历

C语言中，二叉树的非递归遍历同样可以使用栈来实现。以下是三种遍历方式的代码实现：

1. 非递归先序遍历：

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

void preorderTraversal(struct TreeNode* root) {
    struct TreeNode* stack[100];
    int top = -1;
    if(root != NULL) {
        stack[++top] = root;
    }
    while(top != -1) {
        struct TreeNode* node = stack[top--];
        printf("%d ", node->val);
        if(node->right != NULL) {
            stack[++top] = node->right;
        }
        if(node->left != NULL) {
            stack[++top] = node->left;
        }
    }
}

2. 非递归中序遍历：

void inorderTraversal(struct TreeNode* root) {
    struct TreeNode* stack[100];
    int top = -1;
    struct TreeNode* node = root;
    while(node != NULL || top != -1) {
        while(node != NULL) {
            stack[++top] = node;
            node = node->left;
        }
        node = stack[top--];
        printf("%d ", node->val);
        node = node->right;
    }
}

3. 非递归后序遍历：

void postorderTraversal(struct TreeNode* root) {
    struct TreeNode* stack[100];
    int top = -1;
    struct TreeNode* node = root;
    struct TreeNode* lastNodeVisited = NULL;
    while(node != NULL || top != -1) {
        while(node != NULL) {
            stack[++top] = node;
            node = node->left;
        }
        node = stack[top];
        if(node->right == NULL || node->right == lastNodeVisited) {
            printf("%d ", node->val);
            top--;
            lastNodeVisited = node;
            node = NULL;
        } else {
            node = node->right;
        }
    }
}

以上代码中，struct TreeNode是二叉树节点的定义，val表示节点的值，left和right分别表示左子树和右子树。栈的大小可以根据二叉树的大小进行调整。