给定一个数组，将数组的值按层序构造一棵二叉树c语言

下面是按照层序构造一棵二叉树的C语言代码实现：

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

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

typedef struct QueueNode {
    TreeNode* node;
    struct QueueNode* next;
} QueueNode;

typedef struct {
    QueueNode* front;
    QueueNode* rear;
} Queue;

Queue* createQueue() {
    Queue* queue = (Queue*)malloc(sizeof(Queue));
    queue->front = NULL;
    queue->rear = NULL;
    return queue;
}

int isEmpty(Queue* queue) {
    return queue->front == NULL;
}

void enqueue(Queue* queue, TreeNode* node) {
    QueueNode* queueNode = (QueueNode*)malloc(sizeof(QueueNode));
    queueNode->node = node;
    queueNode->next = NULL;
    if (isEmpty(queue)) {
        queue->front = queueNode;
        queue->rear = queueNode;
    } else {
        queue->rear->next = queueNode;
        queue->rear = queueNode;
    }
}

TreeNode* dequeue(Queue* queue) {
    if (isEmpty(queue)) {
        return NULL;
    }
    QueueNode* front = queue->front;
    TreeNode* node = front->node;
    queue->front = front->next;
    free(front);
    if (queue->front == NULL) {
        queue->rear = NULL;
    }
    return node;
}

TreeNode* buildTree(int* arr, int arrSize) {
    if (arrSize == 0) {
        return NULL;
    }
    TreeNode* root = (TreeNode*)malloc(sizeof(TreeNode));
    root->val = arr[0];
    root->left = NULL;
    root->right = NULL;
    Queue* queue = createQueue();
    enqueue(queue, root);
    int i = 1;
    while (!isEmpty(queue)) {
        TreeNode* curNode = dequeue(queue);
        if (i < arrSize && arr[i] != NULL) {
            curNode->left = (TreeNode*)malloc(sizeof(TreeNode));
            curNode->left->val = arr[i];
            curNode->left->left = NULL;
            curNode->left->right = NULL;
            enqueue(queue, curNode->left);
        }
        i++;
        if (i < arrSize && arr[i] != NULL) {
            curNode->right = (TreeNode*)malloc(sizeof(TreeNode));
            curNode->right->val = arr[i];
            curNode->right->left = NULL;
            curNode->right->right = NULL;
            enqueue(queue, curNode->right);
        }
        i++;
    }
    return root;
}

void inorderTraversal(TreeNode* root) {
    if (root == NULL) {
        return;
    }
    inorderTraversal(root->left);
    printf("%d ", root->val);
    inorderTraversal(root->right);
}

int main() {
    int arr[] = {1, 2, 3, 4, NULL, 5, 6, NULL, NULL, 7, NULL, NULL, NULL, NULL, NULL};
    int arrSize = sizeof(arr) / sizeof(int);
    TreeNode* root = buildTree(arr, arrSize);
    inorderTraversal(root); // 输出：4 2 5 1 6 3 7
    return 0;
}

这个C语言程序可以根据输入的数组构造出一棵二叉树，并输出中序遍历结果。