c语言给二叉树的根节点，返回节点值的层序遍历

可以使用队列实现层序遍历。具体过程如下：

1. 将根节点入队列。
2. 当队列非空时，依次出队列队首元素。
3. 将出队元素的值存储到结果数组中。
4. 将出队元素的左右子节点入队列（如果存在）。
5. 重复步骤2-4，直到队列为空。

以下是C语言实现代码：

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

#define MAXSIZE 100

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

typedef struct Queue {
    TreeNode *data[MAXSIZE];
    int front, rear;
} Queue;

void initQueue(Queue *q);
int isEmpty(Queue *q);
int isFull(Queue *q);
void enQueue(Queue *q, TreeNode *node);
TreeNode *deQueue(Queue *q);
void levelOrder(TreeNode *root, int *result, int *returnSize);

void initQueue(Queue *q) {
    q->front = q->rear = 0;
}

int isEmpty(Queue *q) {
    return q->front == q->rear;
}

int isFull(Queue *q) {
    return (q->rear + 1) % MAXSIZE == q->front;
}

void enQueue(Queue *q, TreeNode *node) {
    if (isFull(q)) {
        return;
    }
    q->data[q->rear] = node;
    q->rear = (q->rear + 1) % MAXSIZE;
}

TreeNode *deQueue(Queue *q) {
    if (isEmpty(q)) {
        return NULL;
    }
    TreeNode *node = q->data[q->front];
    q->front = (q->front + 1) % MAXSIZE;
    return node;
}

void levelOrder(TreeNode *root, int *result, int *returnSize) {
    if (root == NULL) {
        return;
    }
    Queue q;
    initQueue(&q);
    enQueue(&q, root);
    while (!isEmpty(&q)) {
        TreeNode *node = deQueue(&q);
        result[(*returnSize)++] = node->val;
        if (node->left != NULL) {
            enQueue(&q, node->left);
        }
        if (node->right != NULL) {
            enQueue(&q, node->right);
        }
    }
}

int main() {
    TreeNode *root = (TreeNode *) malloc(sizeof(TreeNode));
    root->val = 1;
    root->left = (TreeNode *) malloc(sizeof(TreeNode));
    root->left->val = 2;
    root->right = (TreeNode *) malloc(sizeof(TreeNode));
    root->right->val = 3;
    root->left->left = NULL;
    root->left->right = NULL;
    root->right->left = (TreeNode *) malloc(sizeof(TreeNode));
    root->right->left->val = 4;
    root->right->right = (TreeNode *) malloc(sizeof(TreeNode));
    root->right->right->val = 5;
    root->right->left->left = NULL;
    root->right->left->right = NULL;
    root->right->right->left = NULL;
    root->right->right->right = NULL;

    int result[MAXSIZE], returnSize = 0;
    levelOrder(root, result, &returnSize);
    for (int i = 0; i < returnSize; i++) {
        printf("%d ", result[i]);
    }
    printf("\n");

    return 0;
}