请列举5个C语言关于指针高难度笔试考察题目，请用代码举例并写上注释说明

1. 如何用指针实现一个字符串反转的函数？

void reverse_str(char *str) {
    char *left = str; // 左指针指向字符串首地址
    char *right = str + strlen(str) - 1; // 右指针指向字符串末尾

    while (left < right) {
        char temp = *left;
        *left++ = *right;
        *right-- = temp;
    }
}

2. 如何用指针实现一个快速排序算法？

void quick_sort(int *arr, int left, int right) {
    if (left >= right) return;

    int i = left;
    int j = right;
    int pivot = *(arr + left);

    while (i < j) {
        while (i < j && *(arr + j) >= pivot) j--;
        *(arr + i) = *(arr + j);
        while (i < j && *(arr + i) <= pivot) i++;
        *(arr + j) = *(arr + i);
    }

    *(arr + i) = pivot;
    quick_sort(arr, left, i - 1);
    quick_sort(arr, i + 1, right);
}

3. 如何用指针实现一个链表的反转？

typedef struct Node {
    int val;
    struct Node *next;
} Node;

Node* reverse_list(Node *head) {
    Node *prev = NULL;
    Node *curr = head;

    while (curr) {
        Node *temp = curr->next;
        curr->next = prev;
        prev = curr;
        curr = temp;
    }

    return prev;
}

4. 如何用指针实现一个二叉树的中序遍历？

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

void inorder_traversal(TreeNode *root) {
    if (!root) return;

    TreeNode *stack[100]; // 定义一个存放节点指针的栈
    int top = -1; // 栈顶指针

    while (root || top != -1) {
        while (root) {
            stack[++top] = root;
            root = root->left;
        }

        root = stack[top--];
        printf("%d ", root->val);
        root = root->right;
    }
}

5. 如何用指针实现一个矩阵的转置？

void transpose_matrix(int *matrix, int row, int col) {
    int temp;
    for (int i = 0; i < row; i++) {
        for (int j = i + 1; j < col; j++) {
            temp = *(matrix + i * col + j);
            *(matrix + i * col + j) = *(matrix + j * col + i);
            *(matrix + j * col + i) = temp;
        }
    }
}