用c语言实现二叉树的建立对二叉树对二叉树进行先序遍历，并打印层号

下面是用C语言实现二叉树的建立和先序遍历，并打印层号的示例代码：

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

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

void buildTree(Node **root) {
    int val;
    scanf("%d", &val);
    if (val == -1) {
        *root = NULL;
    } else {
        *root = (Node*)malloc(sizeof(Node));
        (*root)->val = val;
        buildTree(&((*root)->left));
        buildTree(&((*root)->right));
    }
}

void preorder(Node *root, int level) {
    if (root == NULL) {
        return;
    }
    printf("Level %d: %d\n", level, root->val);
    preorder(root->left, level + 1);
    preorder(root->right, level + 1);
}

int main() {
    Node *root = NULL;
    printf("Please enter the values of the binary tree in preorder:\n");
    buildTree(&root);
    printf("The result of preorder traversal with level:\n");
    preorder(root, 1);
    return 0;
}

输入格式为先序遍历，其中 `-1` 表示空节点。例如，对于如下二叉树：

      1
     / \
    2   3
   / \   \
  4   5   6

先序遍历为 `1 2 4 -1 -1 5 -1 -1 3 -1 6 -1 -1`，则程序的输出为：

Please enter the values of the binary tree in preorder:
1 2 4 -1 -1 5 -1 -1 3 -1 6 -1 -1
The result of preorder traversal with level:
Level 1: 1
Level 2: 2
Level 3: 4
Level 3: 5
Level 2: 3
Level 3: 6